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diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..d7b82bc --- /dev/null +++ b/.gitattributes @@ -0,0 +1,4 @@ +*.txt text eol=lf +*.htm text eol=lf +*.html text eol=lf +*.md text eol=lf diff --git a/LICENSE.txt b/LICENSE.txt new file mode 100644 index 0000000..6312041 --- /dev/null +++ b/LICENSE.txt @@ -0,0 +1,11 @@ +This eBook, including all associated images, markup, improvements, +metadata, and any other content or labor, has been confirmed to be +in the PUBLIC DOMAIN IN THE UNITED STATES. + +Procedures for determining public domain status are described in +the "Copyright How-To" at https://www.gutenberg.org. + +No investigation has been made concerning possible copyrights in +jurisdictions other than the United States. Anyone seeking to utilize +this eBook outside of the United States should confirm copyright +status under the laws that apply to them. diff --git a/README.md b/README.md new file mode 100644 index 0000000..3a37f22 --- /dev/null +++ b/README.md @@ -0,0 +1,2 @@ +Project Gutenberg (https://www.gutenberg.org) public repository for +eBook #55146 (https://www.gutenberg.org/ebooks/55146) diff --git a/old/55146-0.txt b/old/55146-0.txt deleted file mode 100644 index aecf9bc..0000000 --- a/old/55146-0.txt +++ /dev/null @@ -1,5931 +0,0 @@ -Project Gutenberg's Common Objects of the Microscope, by J. G. Wood - -This eBook is for the use of anyone anywhere in the United States and most -other parts of the world at no cost and with almost no restrictions -whatsoever. You may copy it, give it away or re-use it under the terms of -the Project Gutenberg License included with this eBook or online at -www.gutenberg.org. If you are not located in the United States, you'll have -to check the laws of the country where you are located before using this ebook. - - - -Title: Common Objects of the Microscope - -Author: J. G. Wood - -Editor: E. C. Bousfield - -Illustrator: Tuffen West - -Release Date: July 18, 2017 [EBook #55146] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK COMMON OBJECTS OF THE MICROSCOPE *** - - - - -Produced by Thiers Halliwell, Chris Curnow and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive) - - - - - -Transcriber’s notes: - -Minor punctuation errors have been corrected silently (e.g. missing -full stops after abbreviated words such as Fig), as have the following -misspellings: Bretahing → Breathing, Pedicillaria → Pedicellaria, -Pedicelaria → Pedicellaria, Chœtonotus → Chætonotus, Spurganium -→ Sparganium, veiw → view. Unorthodox spelling and inconsistent -hyphenation has not been altered. Several wrongly numbered -cross-references to Plates and Figures have been corrected. - -Plate VIII (and its accompanying key) was originally displayed -at the beginning of the book, before the Title Page, but has been -repositioned in the body of the text in correct numerical sequence. - - - - - COMMON OBJECTS OF - THE MICROSCOPE - - - BY THE LATE - - Rev. J. G. WOOD, M.A., F.L.S., Etc. - - AUTHOR OF - “COMMON OBJECTS OF THE COUNTRY” “COMMON OBJECTS OF THE SEA-SHORE” - “MY FEATHERED FRIENDS” ETC. ETC. - - - WITH ILLUSTRATIONS BY TUFFEN WEST - - - _SECOND EDITION, REVISED AND RE-WRITTEN, BY_ - - E. C. BOUSFIELD, L.R.C.P.(Lond.) - - AUTHOR OF - “A GUIDE TO THE SCIENCE OF PHOTO-MICROGRAPHY” - - WITH ADDITIONAL ILLUSTRATIONS BY THE REVISER - - - LONDON - - GEORGE ROUTLEDGE AND SONS, Limited - - BROADWAY HOUSE, LUDGATE HILL - - 1900 - - - - -PREFACE TO THE SECOND EDITION - - -The task of revising and bringing up to date a work which has been the -guide, philosopher, and friend of thousands of commencing microscopists -has been, in the present case, one of no small difficulty. On the one -hand, there was the natural desire to interfere as little as possible -with the original work; and on the other, the necessity of rendering -available, to some extent at least, the enormous advance in every -department which has taken place in the thirty-six years which have -elapsed since the work was first offered to the public. The reviser has -done his best not only to fulfil these two objects, but to keep in view -the original purpose of the book. - -In the popular department of pond-life especially, about fifty new -illustrations have been added, mostly from the reviser’s own notebook -sketches. The whole of the botanical part has been revised by one of -our first English authorities, and, in short, no effort has been spared -to make the work as accurate as its necessarily condensed form permits -of. It is hoped, therefore, that it may be found not less useful than -its predecessor by those for whom it is alone intended. - - - - -PREFACE TO THE FIRST EDITION - - -In my two previous handbooks, the “Common Objects” of the Sea-shore and -Country, I could but slightly glance at the minute beings which swarm -in every locality, or at the wonderful structures which are discovered -by the Microscope within or upon the creatures therein described. Since -that time a general demand has arisen for an elementary handbook upon -the Microscope and its practical appliance to the study of nature, and -in order to supply that want this little volume has been produced. - -I must warn the reader that he is not to expect a work that will figure -and describe every object which may be found on the sea-shore or in the -fields, but merely one by which he will be enabled to guide himself -in microscopical research, and avoid the loss of time and patience -which is almost invariably the lot of the novice in these interesting -studies. Upwards of four hundred objects have been figured, including -many representatives of the animal, vegetable, and, mineral kingdoms, -and among them the reader will find types sufficient for his early -guidance. - -Neither must he expect that any drawings can fully render the lovely -structures which are revealed by the microscope. Their form can be -given faithfully enough, and their colour can be indicated; but no pen, -pencil, or brush, however skilfully wielded, can reproduce the soft, -glowing radiance, the delicate pearly translucency, or the flashing -effulgence of living and ever-changing light with which God wills to -imbue even the smallest of His creatures, whose very existence has been -hidden for countless ages from the inquisitive research of man, and -whose wondrous beauty astonishes and delights the eye, and fills the -heart with awe and adoration. - -Owing to the many claims on my time, I left the selection of the -objects to Mr. Tuffen West, who employed the greater part of a year -in collecting specimens for the express purpose, and whose well-known -fidelity and wide experience are the best guarantees that can be -offered to the public. To him I also owe many thanks for his kind -revision of the proof-sheets. My thanks are also due to Messrs. G. and -H. Brady, who lent many beautiful objects, and to Messrs. Baker, the -well-known opticians of Holborn, who liberally placed their whole stock -of slides and instruments at my disposal. - - - - -CONTENTS - - - - CHAPTER I PAGE - - Pleasures and Uses of Microscopy--Development of the - Microscope--Extemporised Apparatus 1 - - - CHAPTER II - - Elementary Principles of Optics--Simple Microscopes--Compound - Microscope--Accessory Apparatus--Cover-glasses--Troughs-- - Condensers--Dissection--Dipping-tubes--Drawing--Measurement 7 - - - CHAPTER III - - Examination of Objects--Principles of Illumination--Mirror - and its Action--Substage Condenser--Use of Bull’s-eye--Opaque - Objects--Photography of Microscopic Objects 28 - - - CHAPTER IV - - Vegetable Cells and their Structure--Stellate Tissues-- - Secondary Deposit--Ducts and Vessels--Wood-Cells--Stomata, - or Mouths of Plants--The Camera Lucida, and Mode of Using-- - Spiral and Ringed Vessels--Hairs of Plants--Resins, Scents, - and Oils--Bark Cells 37 - - - CHAPTER V - - Starch, its Growth and Properties--Surface Cells of Petals-- - Pollen and its Functions--Seeds 63 - - - CHAPTER VI - - Algæ and their Growth--Desmidiaceæ, where found--Diatoms, - their Flinty Deposit--Volvox--Mould, Blight, and Mildew-- - Mosses and Ferns--Mare’s-Tail and the Spores--Common - Sea-weeds and their Growth 78 - - - CHAPTER VII - - Antennæ, their Structure and Use--Eyes, Compound and - Simple--Breathing Organs--Jaws and their Appendages--Legs, - Feet, and Suckers--Digestive Organs--Wings, Scales, and - Hairs--Eggs of Insects--Hair, Wool, Linen, Silk, and - Cotton--Scales of Fish--Feathers--Skin and its Structure-- - Epithelium--Nails, Bone, and Teeth--Blood Corpuscles and - Circulation--Elastic Tissues--Muscle and Nerve 96 - - - CHAPTER VIII - - Pond-Life--Apparatus and Instructions for Collecting - Objects--Methods of Examination--Sponge--Infusoria 132 - - - CHAPTER IX - - Fresh-water Worms--Planarians--Hydra--Polyzoa--Rotifers - Chætonotus--Water-Bears 144 - - - CHAPTER X - - Marine Life--Sponges--Infusoria--Foraminifera--Radiolaria-- - Hydroid Zoophytes--Polyzoa--Worms--Lingual Ribbons and - Gills of Mollusca--Star-Fishes and Sea-Urchins--Cuttle-Fish-- - Corallines--Miscellaneous Objects 154 - - - CHAPTER XI - - Hints on the Preparation of Objects--Preservative Fluids-- - Mounting Media--Treatment of Special Objects 168 - - - CHAPTER XII - - Section-Cutting--Staining 179 - - - - -COMMON OBJECTS OF THE MICROSCOPE - - - - -CHAPTER I - -Pleasures and Uses of Microscopy--Development of the -Microscope--Extemporised Apparatus. - - -Within the last half-century the use of the microscope, not only as -an instrument of scientific research, a tool in the hands of the -investigator of the finer organisation of the world of nature, nor even -as an adjunct to the apparatus of the chemist or the manufacturer, but -as a means of innocent and instructive recreation, has become so firmly -rooted amongst us that it seems hardly necessary to advocate its claims -to attention on any of these grounds. - -So wonderful is the information which it affords, so indispensable is -it in many, if not in all, branches of scientific research, that not -only would the lover of nature be deprived of one of his most valued -sources of information and enjoyment, but some sciences would be -brought absolutely to a standstill if by any conceivable means the -microscope were to be withdrawn from their followers. - -On the other hand, from every improvement in the construction of the -latter, a corresponding enlargement and enlightenment of the fields -reviewed by these sciences has taken place, and the beauty and interest -of the revelations made by its means has attracted an ever-increasing -host of earnest and intelligent volunteers, who have rendered yeoman -service to the cause of knowledge. - -Moreover, so vast is the scope of the instrument, that whilst -discoveries in other fields of research are few and far between, -comparatively speaking, in microscopic science they are of everyday -occurrence, and the number of problems calling for solution by means of -the instrument in question is so vast that even the humblest worker may -be of the greatest assistance. - -In the following pages we propose to carry out, as far as possible -with reference to the microscope, the system followed in the “Common -Objects of the Seashore and of the Country,” and to treat in as simple -a manner as may be of the marvellous structures which are found so -profusely in our fields, woods, streams, shores, and gardens. Moreover, -our observations will be restricted to an instrument of such a class as -to be inexpensively purchased and easily handled, and to those pieces -of supplementary apparatus which can be extemporised at small cost -of money and ingenuity by the observer himself, or obtained of the -opticians for a few shillings. - -With the same view, the descriptions will be given in language as -simple and as free from technicalities as possible, though it must -be remembered that for many of the organisms and structures which we -shall have to describe there are none but scientific names; and since, -moreover, this little work is intended to furnish a stepping-stone -between the very elements of microscopic science, and those higher -developments of it which should be the aim of every worker, it would be -unwise to attempt to invent commonplace appellations for the purpose of -this book, and leave him to discover, when he came to consult works of -reference in any particular subject, that his “simplified” knowledge -had all to be unlearnt, and a new vocabulary acquired. Rather will -it be our purpose to use correct terms, and explain them, as far as -necessary, as we introduce them. - -The commencing microscopist is strongly recommended, whilst not -confining his interest entirely to one branch of research or -observation, to adopt some one as his particular province. - -The opportunities for discovery and original work, which are afforded -by all alike, will be more readily appreciated and utilised by -adopting such a plan than by a general and purposeless distribution of -effort. To mention one or two. The student of the fascinating field of -pond-life will find new organisms awaiting description by the hundred, -and of the old ones, life-histories to make out; if he be attracted -rather to the vegetable inhabitants of the same realm, the diatoms will -furnish him with the opportunity of studying, and perhaps solving, -the enigma of their spontaneous movement, and of watching their -development. The smaller fungi, and indeed the larger ones too, will -amply repay the closest and most laborious study of their habits of -life and processes of development. Since the first edition of this work -was published, the whole subject has been practically revolutionised, -and more remains to be done than has yet been accomplished. - -In short, there is scarcely an organism, even of those best known -and most studied, which is so completely exhausted that persevering -investigation would reveal nothing new concerning it. - -There can be little doubt but that if any worker, with moderate -instrumental means, but with an observant mind, were to set -determinately to work at the study of the commonest weed or the most -familiar insect, he, or she, would by patient labour accomplish work -which would not only be of value to science, but would redound to the -credit of the worker. - -Something like finality appears to have been reached, at least for the -present, in the development of the microscope; and whilst it is beyond -the scope of this work to treat of the refined and costly apparatus -which is essential to useful work in certain departments of research, -the result has, on the whole, been highly favourable to the worker of -moderate means and ambitions, since lenses are now accessible, at the -cost of a few shillings, comparatively speaking, which could not have -been purchased at all when this work first appeared. It is with such -appliances that we have here to deal. The worker whose finances are -restricted must be contented to extemporise for himself many pieces -of apparatus, and will find pleasure and occupation in doing so. And -let him remember, for his encouragement, that many such home-made -appliances will fulfil their purpose quite as well as the imposing -paraphernalia of glittering brass and glass which decorates the table -of the wealthy amateur. It is not the man who possesses the best or -most costly apparatus, but the one who best understands the use of that -which he possesses, that will make the most successful microscopist. A -good observer will discover, with only the aid of a pocket-magnifier, -secrets of Nature which have escaped the notice of a whole army of -dilettante microscopists, in spite of the advantages which, as regards -instruments, the latter may enjoy. - -It is for those who desire to be of the former class that this book -is written, and in the course of the following pages instances will -be given in which the exercise of a small amount of ingenuity and the -expenditure of a few pence will be found equivalent to the purchase of -costly and complicated apparatus. - -An enormous amount of valuable work was done in the earliest days -of microscopy, when the best apparatus available was a single lens, -composed of the bead formed by fusing the drawn-out end of a rod -of glass. Inserted into a plate of metal, or a piece of card, such -a primitive instrument was capable of affording a large amount of -information. Similar instruments are to be purchased for a few pence -at the present day, and are not without their use for purposes of -immediate examination of material. A very common form is a glass -marble, ground flat on one side, and mounted in a tube. The material to -be examined is placed upon the flat side, and is seen magnified to an -extent inversely proportional to the diameter of the sphere of glass. - - - - -CHAPTER II - - Elementary Principles of Optics--Simple Microscopes--Compound - Microscope--Accessory Apparatus--Cover-glasses--Troughs-- - Condensers--Dissection--Dipping-tubes--Drawing--Measurement. - - -Before proceeding to deal with the microscope itself, it may be useful -to give a short summary of the optical laws upon which its working -depends. - -To go into the minutiæ of the matter here would be out of place, but it -will be found very helpful, especially in the matter of illumination, -to acquire some knowledge of, and facility in applying, these -elementary principles. We shall confine our remarks to convex lenses, -as being the form to which all the combinations in the microscope may -be ultimately reduced. - -Every convex lens has one “principal” focus, and an infinite number -of “conjugate” foci. The principal focus is the distance at which it -brings together in one point the rays which fall upon it parallel to -its axis, as shown in Fig. 1, in which _A_ is the axis of the lens _L_, -and the rays _RR_ are brought together in the principal focus _P_. Thus -a ready means of finding the focal length of any lens is to see at what -distance it forms an image of the sun, or of any other distant object, -upon a screen, such as a piece of smooth white cardboard. In the figure -this distance will be _PL_. Conversely, if the source of light be at -_P_, a parallel beam of light will be emitted from the lens. - -[Illustration: Fig. 1.] - -The focal length may, however, be found in another way. When an object -is placed at a distance from a lens equal to twice the principal focal -length of the latter, an image of the object is formed at the same -distance upon the other side of the lens, inverted in position, but of -the same dimensions as the original object. The object and image then -occupy the equal conjugate foci of the lens, so that by causing them -to assume these relative positions, and halving the distance at which -either of them is from the lens, the focal length of the latter is -known. - -These points will be seen on reference to Fig. 2, in which _L_ being -the lens, and _P_ the principal focus, as before, rays from the point -_C_ are brought together at the conjugate focus _C'_, at the same -distance on the other side of _L_. In this case it manifestly does not -matter whether the object be at one or the other of these points. - -[Illustration: Fig. 2.] - -So far we have been dealing with points on the line of the axis of the -lens. The facts mentioned apply equally, however, to rays entering the -lens at an angle to the axis, only that in this case they diverge or -converge, correspondingly, upon the other side. It is evident, from -Fig. 1, that no image is formed of a point situated at the distance -of the principal focus; but Fig. 3, which is really an extension -of Fig. 2, shows how the rays passing along secondary axes form an -inverted image of the same size as the object, when the latter is -situated at twice the focal length of the lens from this last. To -avoid confusion, the bounding lines only are shown, but similar lines -might be drawn from each and every point of the object; and if the -lines _ALA'_, _BL'B'_ be supposed to be balanced at _L_ and _L'_ -respectively, they will indicate the points at which the corresponding -parts of the object and image will be situated along the lines _AB_, -_B'A'_ respectively. Moreover, rays pass from every part of the object -to every part of the lens, so that we must imagine the cones _LAL'_, -_LA'L'_ to be filled with rays diverging on one side of the lens and -converging on the other. - -The image so formed is a “real” image,--that is to say, it can be -thrown upon a screen. - -[Illustration: Fig. 3.] - -The microscopic image, on the other hand, is a virtual image, which can -be viewed by the eye but cannot be thus projected, for it is formed by -an object placed nearer to the lens than the principal focal length of -the latter, so that the rays diverge, instead of converging, as they -leave the lens, and the eye looks, as it were, back along the path in -which the rays appear to travel, and so sees an enlarged image situated -in the air, farther away than the object, as shown in Fig. 4. In this -case, as the diagram shows, the image is upright, not inverted. - -Images of the latter class are those formed by simple microscopes, of -the kind described in the previous chapter. In the compound microscope -the initial image, formed by the object-glass, is further magnified by -another set of lenses, forming the eye-piece, by which the diverging -rays of the virtual image are brought together to a focus at the -eye-point; and when viewed directly, the eye sees an imaginary image, -as in a simple microscope, whilst, when the rays are allowed to fall -upon a screen, they form a real image of the object, larger or smaller, -as the screen is farther from or nearer to the eye-point. - -[Illustration: Fig. 4.] - -These remarks must suffice for our present purpose. Those who are -sufficiently interested in the subject to desire to know more of the -delicate corrections to which these broad principles are subjected in -practice, that objectives may give images which are clear and free from -colour, to say nothing of other faults, will do well to consult some -such work as Lommel’s _Optics_, in the International Science Series. - -In following a work such as the present one, the simple microscope, -in some form or other, will be found almost indispensable. It will be -required for examining raw material, such as leaves or other parts of -plants, for gatherings of life in fresh or salt water, for dissections. -With such powers as those with which we shall have to deal, it will -rarely happen that, for example, a bottle of water in which no life is -visible will be worth the carrying-home; whilst, on the other hand, a -few months’ practice will render it not only possible, but easy, not -only to recognise the presence, but to identify the genus, and often -even the species, of the forms of life present. Moreover, these low -powers, affording a general view of the object, allow the relation -to each other of the details revealed by the power of the compound -microscope to be much more easily grasped. A rough example may suffice -to illustrate this. A penny is a sufficiently evident object to the -naked eye, but it will require a sharp one to follow the details in -Britannia’s shield, whilst the minute scratches or the bloom upon the -surface would be invisible in detail without optical aid. Conversely, -however, it would be rash to conclude from an examination of a portion -of the surface with the microscope alone that the portion in view was -a sample of the whole surface. The more the surface is magnified, -the less are the details grasped as a whole, and for this reason the -observer is strongly recommended to make out all that he can of an -object with a simple magnifier before resorting to the microscope. - -For general purposes, the intending observer cannot do better than -supply himself with a common pocket-magnifier, with one, two, or three -lenses, preferably the last, as although the absolute performance -is not so accurate, the very considerable range of power available -by using the lenses singly, or in various combinations, is of great -advantage. Such a magnifier may be obtained from Baker for about -three-and-sixpence, or, with the addition of a powerful Coddington lens -(Fig. 5) in the same mount, for nine shillings more. Aplanatic lenses, -such as the one shown in section in Fig. 6, with a much flatter field -of vision, but of one power only each, cost about fifteen shillings, -and a simple stand, which adapts them for dissecting purposes, may -be obtained of the same maker for half a crown, or may easily be -extemporised from a cork sliding stiffly on an iron rod set in a heavy -foot, the cork carrying a loop of wire terminating in a ring which -carries the lens. - -[Illustration: Fig. 5.] - -[Illustration: Fig. 6.] - -So much may suffice for the simple microscope. We pass on now to the -consideration of the instrument which forms the subject of the present -work, an instrument which, whilst moderate in price, is yet capable -of doing a large amount of useful and valuable work in the hands of -a careful owner, and of affording him a vast amount of pleasure and -recreation, even if these be his only objects in the purchase, though -it is difficult to understand that, an insight being once attained into -the revelations effected by the instrument, without a desire being -excited in any intelligent mind to pursue the subject as a study as -well as a delightful relaxation. The microscope described, and adopted -as his text by the author of this work, is still made, and has shared -to a very considerable extent in the general improvement of optical -apparatus which has taken place during the last thirty years. It is to -be obtained from Baker, 244 High Holborn, and is provided with most -of the apparatus which will be found indispensable by the beginner, -costing, with a case in which to keep it, the modest sum of three -guineas. - -[Illustration: Fig. 7.] - -If this instrument represent the limit of the purchaser’s power of -purse, he may very well make it answer his purpose for a considerable -time. The same instrument, however, with separate objectives of good -quality, together with a bull’s-eye condenser (an almost indispensable -adjunct), a plane mirror in addition to a concave one, and a simple but -efficient form of substage condenser, may be obtained for £5, 12s. 6d., -and the extra outlay will be well repaid by the advantage in working -which is gained by the possession of the additional apparatus. - -[Illustration: Fig. 8.] - -A still better stand, and one which is good enough for almost any -class of work, is that shown in Fig. 8, which is known as the -“Portable” microscope. In this instrument the body is made up of -two tubes, so that the length may be varied at will, and this gives -a very considerable range of magnification without changing the -object-glass, a great convenience in practice; whilst the legs fold -up for convenience of carriage, so that the whole instrument, with -all necessary appliances, may be readily packed in a corner of a -portmanteau for transport to the country or seaside. - -The objectives supplied with the simplest form of microscope above -referred to are combinations of three powers in one, and the power is -varied by using one, two, or three of these in combination. This form -of objective is very good, as far as it goes, though it is impossible -to correct such a combination with the accuracy which is possible in -manufacturing one of a fixed focal length. - -Perhaps the best thing for the beginner to do would be to purchase the -combination first, and, later on, to dispose of it and buy separate -objectives of, say, one-inch, half-inch, and quarter-inch focal -lengths. It may be explained here, that when a lens is spoken of as -having a certain focal length, it is meant that the magnification -obtained by its use is the same, at a distance of ten inches from the -eye, as would be obtained by using a simple sphere of glass of the same -focal length at the same distance. This, of course, is simply a matter -of theory, for such lenses are never used actually. - -[Illustration: Fig. 9.] - -Of accessory apparatus, we may mention first the stage forceps (Fig. 9, -_a_). These are made to fit into a hole upon the stage, so as to be -capable of being turned about in any direction, with an object in their -grasp, and for some purposes, especially such as the examination of a -thin object, say the edge of a leaf, they are extremely useful. - -[Illustration: Fig. 10.] - -The live box, in which drops of water or portions of water-plants, -or the like, may be examined, will be found of great service. By -adjustment of the cap upon the cylinder, with proper attention to -the thickness of the cover-glass in the cap, any required amount of -pressure, from that merely sufficient to fix a restless object to an -amount sufficient to crush a resistent tissue, may easily be applied, -whilst the result of the operation is watched through the microscope. -This proceeding is greatly facilitated if the cap of the live-box be -slotted spirally, with a stud on the cylinder, so that a half-turn of -the cap brings the glasses into contact. By this means the pressure may -be adjusted with the greatest nicety. - -In examining delicate objects, such as large infusoria, which -invariably commit suicide when pressure is applied, a good plan is to -restrict their movements by placing a few threads of cotton-wool, well -pulled out, in the live-box with the drop of water. - -A variety of instruments has been invented for the same purpose, of -which Beck’s parallel compressorium may be mentioned as the most -efficient, though it is somewhat complicated, and consequently -expensive, costing about twenty-five shillings. - -A few glass slips and cover-glasses will also be required. The latter -had better be those known as “No. 2,” since the beginner will find it -almost impossible to clean the thinner ones satisfactorily without -a large percentage of fractures. The safest way is to boil the thin -glass circles in dilute nitric acid (half acid, half water) for a -few minutes, wash well in several waters, first tap-water and then -distilled, and finally to place the covers in methylated spirit. When -required for use, the spirit may be burnt off by applying a light, the -cover-glass, held in a pair of forceps, being in no way injured by the -process. - -In addition to the glass slides, the observer will find it advisable to -be provided with a few glass troughs, of various thicknesses, in which -portions of water-plants, having organisms attached to them, may be -examined. Confined in the live-box, many of the organisms ordinarily -found under such circumstances can rarely be induced to unfold their -beauties, whilst in the comparative freedom of the trough they do so -readily. The troughs may be purchased, or may be made of any desired -shape or size by cutting strips of glass of a thickness corresponding -to the depth desired, cementing these to a glass slide somewhat larger -than the ordinary one, and cementing over the frame so formed a piece -of thin glass, No. 3; the best material to use as cement being marine -glue of the best quality, or, failing this, Prout’s elastic glue, which -is much cheaper, but also less satisfactory. The glass surface must -be made, in either case, sufficiently hot to ensure thorough adhesion -of the cement, as the use of any solvent entails long waiting, and -considerable risk of poisoning the organisms. A useful practical hint -in the use of these troughs is that the corners, at the top, should be -greased slightly, otherwise the water finds its way out by capillary -attraction, to the detriment of the stage of the microscope. - -Of optical accessories, the bull’s-eye is almost the most valuable. So -much may be effected by its means alone, in practised hands, that it is -well worth the while of the beginner to master its use thoroughly, and -the methods of doing so will be explained in the succeeding chapter. - -The substage condenser, too, even in its most simple form, is an -invaluable adjunct, even though it be only a hemisphere of glass, -half an inch or so in diameter, mounted in a rough sliding jacket to -fit underneath the stage. Such an instrument, properly fitted, will -cost about fifteen shillings, but the ingenious worker will easily -extemporise one for himself. - -[Illustration: Fig. 11.] - -Many plants and animals require to be dissected to a certain extent -before the details of their structure can be made out, and for this -purpose the naked eye alone will rarely serve. The ordinary pocket -magnifier, however, if mounted as described in a preceding chapter, -will greatly facilitate matters, and the light may be focused upon the -object by means of the bull’s-eye condenser, as shown in Fig. 11. In -the figure the latter is represented as used in conjunction with the -lamp, but daylight is preferable if it be available, the strain upon -the eyes being very much less than with artificial light. Two blocks -of wood, about four inches high, will form convenient rests for the -hands, a plate of glass being placed upon the blocks to support the -dish, and a mirror being put in the interspace at an angle of 45° or -so if required. A piece of black paper may be laid upon the mirror if -reflected light alone is to be used. - -As all delicate structures are dissected under fluid, a shallow dish -is required. For this purpose nothing is better than one of the dishes -used for developing photographic negatives. The bottom of the dish is -occupied by a flat cork, to which a piece of flat lead is attached -below, and the object having been pinned on to the cork in the required -position, the fluid is carefully run in. This fluid will naturally vary -according to the results desired to be obtained, but it must not be -plain water, which so alters all cellular structures as to practically -make them unrecognisable under the microscope. Nothing could be better -than a 5 per cent. solution of formalin, were it not for the somewhat -irritating odour of this fluid, since it at once fixes the cells and -preserves the figure. For many purposes a solution of salt, in the -proportion of a saltspoonful of the latter to a pint of water, will -answer well for short dissections. For more prolonged ones, a mixture -of spirit-and-water, one part of the former to two of the latter, -answers well, especially for vegetable structures. When the dilution -is first made, the fluid becomes milky, unless pure spirit be used, -but with a little trouble the Revenue authorities may be induced to -give permission for the use of pure methylated spirit, which answers -every purpose. The trouble then is that not less than five gallons can -be purchased, an _embarras de richesses_ for the average microscopist, -but, after all, the spirit is extremely cheap, and does not deteriorate -by keeping. - -When the dissection in either of these media is completed, spirit -should be gradually added to bring the strength up to 50 per cent., in -which the preparation may remain for a day or two, after which it is -gradually brought into pure spirit, or into water again, according to -the medium in which it is to be mounted. - -[Illustration: Fig. 12.] - -As to the tools required, they are neither numerous nor expensive. -Fine-pointed but strong forceps (Fig. 9, _c_), curved and straight; -a couple of pairs of scissors, one strong and straight, the other -more delicate, and having curved blades, and a few needles of various -thicknesses and curves, are the chief ones. The latter may be made by -inserting ordinary needles, for three-fourths of their length, into -sticks of straight-grained deal (ordinary firewood answers best), and -thereafter bending them as required. A better plan, however, is to be -provided with a few of the needle-holders shown in Fig. 9, _b_. These -are very simple and inexpensive, and in them broken needles are readily -replaced by others. Dipping-tubes, such as are shown in Fig. 12, will -also be extremely useful for many purposes. These are very easily made -by heating the centre of a piece of soft glass tubing of the required -size, and, when it is quite red-hot, drawing the ends apart. The fine -tube in the centre should now be divided by scratching it with a fine -triangular file, and the scratch may of course be made at such a -point as to afford a tube of the required fineness. The edges should -be smoothed by holding them in the flame until they just run (not -melt, or the tube will close). These tubes can often be made to supply -the place of a glass syringe. They may be used either for sucking up -fluid or for transferring it, placing the finger over the wide end, -allowing the tube to fill by displacement of air, and then re-closing -it with the finger. This last method is especially useful for -transferring small objects from one receptacle to another. In speaking -of the dissection of objects, it should have been mentioned that the -microscope itself may, under careful handling, be made to serve very -well, only, as the image is reversed, it is almost impossible to work -without using a prism to re-erect the image. Such a prism is shown in -Fig. 13. The microscope is placed vertically, and the observer, looking -straight into the prism, sees all the parts of the image in their -natural positions. This appliance is extremely useful for the purpose -of selecting small objects, and arranging them on slides in any desired -manner. A few words may be added as to the reproduction of the images -of objects. - -[Illustration: Fig. 13.] - -The beginner is strongly recommended to practise himself in this -from the outset. Even a rough sketch is worth pages of description, -especially if the magnification used be appended; and even though -the worker may be devoid of artistic talent, he will find that with -practice he will acquire a very considerable amount of facility in -giving truthful outlines at least of the objects which he views. -Various aids have been devised for the purpose of assisting in the -process. The simplest and cheapest of these consists of a cork cut so -as to fit round the eye-piece. Into the cork are stuck two pins, at an -angle of 45° to the plane of the cork, and, the microscope being placed -horizontally, a thin cover-glass is placed upon the two pins, the light -being arranged and the object focused after the microscope is inclined. -On looking vertically down upon the cover-glass, a bright spot of light -will be seen, and as the eye is brought down into close proximity with -it the spot will expand and allow the observer to see the whole of the -image without looking into the microscope. If a sheet of paper be now -placed upon the table at the place occupied by the image so projected, -the whole of the details will be clearly seen, as will also the point -of a pencil placed upon the paper in the centre of the field of view; -and, after a little practice, it will be found easy to trace round the -chief details of the object. Two points require attention. The first is -that if the light upon the paper be stronger than that in the apparent -field of the microscope, the image will not be well seen, or if the -paper be too feebly lighted, it will be difficult to keep the point of -the pencil in view. The light from the microscope is thrown into the -eye, and the view of the image upon the paper is the effect of a mental -act, the eye looking out in the direction from which the rays appear -to come. The paper has therefore to be illuminated independently, and -half the battle lies in the adjustment of the relative brightness of -image and paper. The second point is, that it is essential to fix one -particular point in the image as the starting-point of the drawing, and -this being first depicted, the image and drawing of this point must be -kept always coincident, or the drawing will be distorted, since the -smallest movement of the eye alters the relations of the whole. The -reflector must be placed at an angle of 45°, or the field will be oval -instead of circular. The simple form of apparatus just described has -one drawback, inasmuch as the reflection is double, the front and back -of the cover-glass both acting as reflectors. The image from the latter -being much the more feeble of the two, care in illumination will do -much to eliminate this difficulty; but there are various other forms -in which the defect in question is got rid of. The present writer has -worked with all of them, from the simple neutral tint reflector of -Beale to the elaborate and costly apparatus of Zeiss, and, upon the -whole, thinks that he prefers the cover-glass to them all. - -A very simple plan, not so mechanical as the last-named, consists in -the use of “drawing-squares,” which are delicate lines ruled upon a -piece of thin glass, and dropped into the eye-piece so that the lines -rest upon the diaphragm of the eye-piece, and therefore are in focus -at the same time as the object. By the use of these, in combination -with paper similarly ruled, a diagram of any required size can be drawn -with very great facility. The squares, if compared with a micrometer, -will furnish an exact standard of magnitude for each object-glass -employed. The micrometer is a piece of thin glass upon which are ruled -minute divisions of an inch or a millimeter. Suppose the micrometer to -be placed under the microscope when the squares are in the eye-piece, -and it be found that each division corresponds with one square of -the latter, then, if the micrometric division be one one-hundredth -of an inch, and the squares upon the paper measure one inch, it is -clear that the drawing will represent the object magnified a hundred -“diameters”; if two divisions of the micrometer correspond to three -squares, the amplification will be a hundred and fifty diameters; if -three divisions correspond to two squares, sixty-six diameters, and -so on. If a draw-tube be used, it will be necessary to know the value -of the squares at each inch of the length, if they are to be used for -measuring magnification. - - - - -CHAPTER III - - Examination of Objects--Principles of Illumination--Mirror - and its Action--Substage Condenser--Use of Bull’s-eye--Opaque - Objects--Photography of Microscopic Objects. - - -So much depends upon a right method of employing the microscope, as -regards both comfort and accuracy, that we propose to devote a little -space to the consideration of the subject. - -Let us first warn the intending observer against the use of powers -higher than are required to bring out the details of the object. Mere -magnification is of very little use: it increases the difficulties both -of illumination and of manipulation, and, as already said, interferes -with that grasp of the object which it is most desirable to obtain. -Rather let the beginner lay himself out to get the very most he can out -of his lowest powers, and he will find that, by so doing, he will be -able far better to avail himself of the higher ones when their use is -indispensable. - -The essential means to this end is a mastery of the principles of -illumination, which we now proceed to describe. - -We suppose the microscope to be inclined at an angle of about 70° to -the horizontal, with a low-power objective attached to it, a one-inch -by preference. Opposite to the microscope, and about a foot away from -it, is a lamp with the edge of the flame presented to the microscope, -the concave mirror of which is so arranged as to receive the rays from -the flame and direct them up the tube of the microscope. Upon the stage -is placed a piece of ground-glass, and the mirror-arm is now to be -moved up or down upon its support until the ground-glass receives the -maximum of illumination, which it will do when the lamp-flame is at one -conjugate focus of the mirror and the ground-glass at the other. The -focus will not be an image of the flame, but a bar of light. - -If an object be now placed upon the stage, instead of the ground-glass, -and the objective focused upon it, it will, if the mirror be properly -adjusted, be brilliantly illuminated. - -It will be understood that every concave mirror has a focus, and -converges the rays which fall upon it to this focus, behaving exactly -like a convex lens. The principal focus of a concave mirror is its -radius of curvature, and this is not difficult to determine. Place side -by side a deep cardboard box and the lamp, so that the concave mirror -may send the rays back, along a path only slightly inclined to that by -which they reached it, to the bottom of the box. The lamp and box being -equidistant from the mirror, it is evident that when the mirror forms -an image of the former upon the latter equal to the flame in size, we -have the equivalent of the equal conjugate foci shown in Fig. 2. Now -move the box to the distance from the mirror which corresponds to the -distance of the stage of the microscope from the mirror when the latter -is in position upon the microscope, and then move the lamp to or fro -until the mirror casts a sharp image of the flame upon the bottom of -the box, which is not to be moved. The lamp distance so found will be -the correct one for working with the concave mirror. The writer is led -to lay special stress upon this matter, from the fact that he almost -invariably finds that the mirror is arranged to be used for parallel -rays, _i.e._ for daylight, and is therefore fixed far too close to the -stage to be available for correct or advantageous working with the -lamp, unless, indeed, the bull’s-eye condenser be used, as hereinafter -described, to parallelise the rays from the lamp. - -Work done with the concave mirror can, however, under the most -favourable conditions, only be looked upon as a _pis aller_. The -advantages gained by the use of some substage condenser, even the most -simple, in conjunction with the plane mirror, or even without any -mirror at all, are so manifold that the beginner is strongly urged -to provide himself with some form or other of it, and we now proceed -to describe the way in which this should be used to produce the best -effect. - -To reduce the problem to its most simple elements, turn the mirror -altogether out of the way, and place the microscope upon a block at -such a height as shall be convenient for observation, and shall allow -the rays from the lamp, placed in a line with it on the table, to shine -directly into the tube of the microscope. Ascertain that this is so -by removing both objective and eye-piece and looking down the tube, -when the flame should be seen in the centre, edgewise. Now replace -the eye-piece, and screw on to the tube the one-inch combination or -objective. Place upon the stage an object, preferably a round diatom or -an echinus-spine, and focus it as sharply as possible. Now place the -substage condenser in its jacket, and slide it up and down until the -image of the object is bisected by the image of the flame. - -The centre of the object will now be brilliantly illuminated by rays -travelling in the proper direction for yielding the best results. -The object is situated at the common focus of the microscope and the -condenser, and, whatever means of illumination be adopted, this is the -result which should always be aimed at. - -Satisfactory as this critical arrangement is, however, from a -scientific point of view, it has its drawbacks from an artistic and -æsthetic one. It is not pleasant, for most purposes, to have merely the -centre of an object lighted up, and we have now to consider how the -image of the edge of the flame may be so expanded as to fill the field -without sacrificing more than a very small fraction of the accuracy of -the arrangement just attained. - -Referring to Fig. 1, we see that if we place the lamp at the principal -focus of a lens, it will emit a bundle of parallel rays equal in -diameter to the diameter of the lens. This is the key of the position. -We cannot place the lamp at an infinite distance from the substage -condenser, but we can supply the latter with rays approximately -parallel, so that it shall bring them to a focus upon the object -at very nearly its own principal focus. This we do by means of the -bull’s-eye condenser. Place the latter, with its flat side toward the -edge of the flame, and at its principal focal distance (the method of -determining which has already been described) from the latter, so that -the bundle of parallel rays which issue from it may pass up to the -substage condenser. On examining the object again, it will be found -that, after slight adjustments of the position of the bull’s-eye have -been made, the object lies in the centre of an evenly and brilliantly -lighted field. - -It may be necessary to place the bull’s-eye a little farther from or -nearer to the lamp, or to move it a little to one side or the other, -but when it is at the correct distance, and on the central line between -the lamp and the substage condenser, at right angles to this line, -the effects will be as described. It may help in securing this result -if we mention that when the bull’s-eye is too far from the lamp, the -image of the flame is a spindle-shaped one; whilst, when the distance -between the two is too short, _i.e._ less than the principal focal -length of the lens, the field is crossed by a bar or light, the ends of -which are joined by a ring, whilst on either side of the bar there is a -semi-circular dark space. - -We have hitherto supposed the objects viewed to be transparent, but -there are many, of great interest, which are opaque, and call for other -means of illumination. Of these there are several. The simplest and, in -many ways, the best is to use the bull’s-eye condenser to bring to a -focus upon the object the rays of light from some source placed above -the stage of the microscope. If light can be obtained from the sun -itself, no lens will be needed to concentrate it; and indeed, if this -were done, there would be considerable risk of burning the object. The -light from a white cloud, however, with the help of the bull’s-eye, -answers admirably. At night-time an artificial source of light, the -more intense and the more distant the better, is required. For most -cases, and with powers not higher than one inch, a good paraffin lamp, -placed about two feet away from the stage, and on one side of it, so as -to be about a foot above the level of the object, will give all that is -needed. Such a lamp is shown in Fig. 14. Low magnifications are, as a -rule, all that is called for in this method. - -Lieberkuhn’s condensers are useful aids, but are somewhat expensive. -They are concave mirrors, which are so adjusted to the objective that -the latter and the reflector come into focus together, the light being -sent in from below, or from one side. - -One other method of illumination must be mentioned before leaving the -topic, and this is the illumination of objects upon a “dark field.” -With suitable subjects, and when carefully managed, there is no method -which gives more beautiful effects, and it has the great advantage of -allowing the object to be brilliantly lighted, without the strain to -the eyes which is involved in such lighting by the usual method of -direct illumination. - -[Illustration: Fig. 14.] - -It consists essentially in allowing the light to fall upon the object -from below, at such an angle that none of it can enter the objective -directly. Thus the concave mirror, turned as far as possible to one -side, and reflecting on to the object the rays from the lamp placed -upon the opposite side, will give very fair results with low powers; -this plan, however, is capable of but very limited application. Again, -a disc of black paper may be stuck on to the middle of the bull’s-eye, -and the latter be placed below the stage between it and the mirror. In -this case everything depends upon the size of the disc, which, if too -small, will not give a black ground, and if too large will cut off all -light from the object. - -The best and only really satisfactory plan is to arrange the -illumination with the substage condenser, as previously described, and -then to place below the lens of the latter a central stop of a suitable -size, which can only be determined by trial. When this has been done -the object will be seen brilliantly illuminated upon a field of velvety -blackness. Such stops are supplied with the condenser. - -We have devoted a considerable portion of space to this question, since -it is, of all others, the most important to a successful, satisfactory, -and reliable manipulation of the microscope; but even now, only the -main points of the subject have been touched upon, and the worker -will find it necessary to supplement the information given by actual -experiment. A few failures, rightly considered, will afford a great -amount of information, but those who desire to go thoroughly into the -matter are recommended to consult the present writer’s _Guide to the -Science of Photomicrography_, where it is treated at much greater -length, as an essential part of the subject-matter of the book. - -It may be added here, that no method of reproducing the images of -objects is on the whole so satisfactory as the photographic one; and -whilst a lengthened reference to the topic would be out of place in -a work of the character of the present one, the one just mentioned -will be found to contain all that is necessary to enable the beginner -to produce results which, for faithfulness and beauty, far excel any -drawing, whilst they have the additional advantage that they can, if -required, be exhibited to hundreds simultaneously. - - - - -CHAPTER IV - - Vegetable Cells and their Structure--Stellate Tissues--Secondary - Deposit--Ducts and Vessels--Wood-Cells--Stomata, or Mouths of - Plants--The Camera Lucida, and Mode of Using--Spiral and Ringed - Vessels--Hairs of Plants--Resins, Scents, and Oils--Bark Cells. - - -We will now suppose the young observer to have obtained a microscope -and learned the use of its various parts, and will proceed to work -with it. As with one or two exceptions, which are only given for the -purpose of further illustrating some curious structure, the whole -of the objects figured in this work can be obtained without any -difficulty, the best plan will be for the reader to procure the plants, -insects, etc., from which the objects are taken, and follow the book -with the microscope at hand. It is by far the best mode of obtaining a -systematic knowledge of the matter, as the quantity of objects which -can be placed under a microscope is so vast that, without some guide, -the tyro flounders hopelessly in the sea of unknown mysteries, and -often becomes so bewildered that he gives up the study in despair of -ever gaining any true knowledge of it. I would therefore recommend the -reader to work out the subjects which are here mentioned, and then -to launch out for himself on the voyage of discovery. I speak from -experience, having myself known the difficulties under which a young -and inexperienced observer has to labour in so wide a field, without -any guide to help him to set about his work in a systematic manner. - -The objects that can be most easily obtained are those of a vegetable -nature, as even in London there is not a square, an old wall, a -greenhouse, a florist’s window, or even a greengrocer’s shop, that will -not afford an exhaustless supply of microscopic employment. Even the -humble vegetables that make their daily appearance on the dinner-table -are highly interesting; and in a crumb of potato, a morsel of greens, -or a fragment of carrot, the enthusiastic observer will find occupation -for many hours. - -Following the best examples, we will commence at the beginning, and see -how the vegetable structure is built up of tiny particles, technically -called “cells.” - -That the various portions of every vegetable should be referred to -the simple cell is a matter of some surprise to one who has had no -opportunity of examining the vegetable structure, and indeed it does -seem more than remarkable that the tough, coarse bark, the hard -wood, the soft pith, the green leaves, the delicate flowers, the -almost invisible hairs, and the pulpy fruit, should all start from -the same point, and owe their origin to the simple vegetable cell. -This, however, is the case; and by means of a few objects chosen from -different portions of the vegetable kingdom, we shall obtain some -definite idea of this curious phenomenon. - - -I. - - FIG. - 1. Strawberry, cellular tissue - 2. Buttercup leaf, internal layer - 3. Privet, Seed Coat, showing star-shaped cells - 4. Rush, Star-shaped cells - 5. Mistletoe, cells with ringed fibre - 6. Cells from interior of Lilac bud - 7. Bur-reed (_Sparganium_), square cells from leaf - 8. Six-sided cells, from stem of Lily - 9. Angular dotted cells, rind of Gourd - 10. Elongated ringed cells, anther of Narcissus - 11. Irregular star-like tissue, pith of Bulrush - 12. Six-sided cells, pith of elder - 13. Young cells from Wheat - 14. Do. rootlets of Wheat - 15. Wood-cells, Elder - 16. Glandular markings and resin, “Cedar” pencil - 17. Do. Yew - 18. Scalariform tissue, Stalk of Fern - 19. Dotted Duct, Willow - 20. Do. Stalk of Wheat - 21. Wood-cell, Chrysanthemum - 22. Do. Lime-tree - 23. Dotted Duct, Carrot - 24. Cone-bearing wood, Deal - 25. Cells, outer coat, Gourd - 26. Ducts, Elm - 27. Cellular tissue, Stalk of Chickweed - 28. Holly-berry, outer coat - -[Illustration: I.] - -On Plate I. Fig. 1, may be seen three cells of a somewhat globular -form, taken from the common strawberry. Any one wishing to examine -these cells for himself may readily do so by cutting a very thin slice -from the fruit, putting it on a slide, covering it with a piece of thin -glass (which may be cheaply bought at the optician’s, together with the -glass slides on which the objects are laid), and placing it under a -power of two hundred diameters. Should the slice be rather too thick, -it may be placed in the live-box and well squeezed, when the cells will -exhibit their forms very distinctly. In their primary form the cells -seem to be spherical; but as in many cases they are pressed together, -and in others are formed simply by the process of subdivision, the -spherical form is not very often seen. The strawberry, being a soft and -pulpy fruit, permits the cells to assume a tolerably regular form, and -they consequently are more or less globular. - -Where the cells are of nearly equal size, and are subjected to equal -pressure in every direction, they force each other into twelve-sided -figures, having the appearance under the microscope of flat six-sided -forms. Fig. 8, in the same Plate, taken from the stem of a lily, is -a good example of this form of cell, and many others may be found in -various familiar objects. - -We must here pause for a moment to define a cell before we proceed -further. - -The cell is a close sac or bag formed of a substance called from its -function “cellulose,” and containing certain semi-fluid contents as -long as it retains its life. In the interior of the cell may generally -be found a little dark spot, termed the “núcleus,” and which may be -seen in Fig. 1, to which we have already referred. The object of the -nucleus is rather a bone of contention among the learned, but the best -authorities on this subject consider it to be the vital centre of the -cells, to and from which tends the circulation of the protoplasm, and -which is intimately connected with the growth and reproduction of the -cell. On looking a little more closely at the nucleus, we shall find it -marked with several small light spots, which are termed “nucléoli.” - -On the same Plate (Fig. 2) is a pretty group of cells taken from the -internal layer of the buttercup leaf, and chosen because they exhibit -the series of tiny and brilliant green dots to which the colour of the -leaf is due. The technical name for this substance is “chlorophyll,” -or “leaf-green,” and it may always be found thus dotted in the leaves -of different plants, the dots being very variable in size, number, and -arrangement. A very fine object for the exhibition of this point is the -leaf of _Anácharis_, the “Canadian timber-weed,” to be found in almost -every brook and river. It also shows admirably the circulation of the -protoplasm in the cell. - -In the centre of the same Plate (Fig. 12) is a group of cells from -the pith of the elder-tree. This specimen is notable for the number -of little “pits” which may be seen scattered across the walls of the -cells, and which resemble holes when placed under the microscope. -In order to test the truth of this appearance, the specimen was -coloured blue by the action of iodine and dilute sulphuric acid, when -it was found that the blue tint spread over the pits as well as the -cell-walls, showing that the membrane is continuous over the pits. - -Fig. 7 exhibits another form of cell, taken from the Spargánium, or -bur-reed. These cells are tolerably equal in size, and have assumed a -square shape. They are obtained from the lower part of the leaf. The -reader who has any knowledge of entomology will not fail to observe the -similarity in form between the six-sided and square cells of plants and -the hexagonal and square facets of the compound eyes of insects and -crustaceans. In a future page these will be separately described. - -Sometimes the cells take most singular and unexpected shapes, several -examples of which will be briefly noticed. - -In certain loosely made tissues, such as are found in the rushes and -similar plants, the walls of the cells grow very irregularly, so -that they push out a number of arms which meet each other in every -direction, and assume the peculiar form which is termed “stellate,” -or star-shaped tissue. Fig. 3 shows a specimen of stellate tissue -taken from the seed-coat of the privet, and rather deeply coloured, -exhibiting clearly the beautiful manner in which the arms of the -various stars meet each other. A smaller group of stellate cells taken -from the stem of a large rush, and exemplifying the peculiarities of -the structure, are seen in Fig. 4. - -The reader will at once see that this mode of formation leaves a vast -number of interstices, and gives great strength with little expenditure -of material. In water-plants, such as the reeds, this property is -extremely valuable, as they must be greatly lighter than the water in -which they live, and at the same time must be endowed with considerable -strength in order to resist its pressure. - -A less marked example of stellate tissue is given in Fig. 11, where -the cells are extremely irregular, in their form, and do not coalesce -throughout. This specimen is taken from the pithy part of a bulrush. -There are very many other plants from which the stellate cells may be -obtained, among which the orange affords very good examples, in the -so-called “white” that lies under the yellow rind, a section of which -may be made with a very sharp razor, and placed in the field of the -microscope. - -Looking toward the bottom of the Plate, and referring to Fig. 27, the -reader will observe a series of nine elongated cells, placed end to -end, and dotted profusely with chlorophyll. These are obtained from -the stalk of the common chickweed. Another example of the elongated -cell is seen in Fig. 14, which is a magnified representation of the -rootlets of wheat. Here the cells will be seen set end to end, and each -containing its nucleus. On the left hand of the rootlet (Fig. 13) is a -group of cells taken from the lowest part of the stem of a wheat plant -which had been watered with a solution of carmine, and had taken up a -considerable amount of the colouring substance. Many experiments on -this subject were made by the Rev. Lord S. G. Osborne, and may be seen -at full length in the pages of the _Microscopical Journal_, the subject -being too large to receive proper treatment in the very limited space -which can here be given to it. It must be added that later researches -have caused the results here described to be gravely disputed. - -Fig. 9 on the same Plate exhibits two notable peculiarities--the -irregularity of the cells and the copiously pitted deposit with which -they are covered. The irregularity of the cells is mostly produced by -the way in which the multiplication takes place, namely, by division -of the original cell into two or more new ones, so that each of these -takes the shape which it assumed when a component part of the parent -cell. In this case the cells are necessarily very irregular, and when -they are compressed from all sides they form solid figures of many -sides, which, when cut through, present a flat surface marked with a -variety of irregular outlines. This specimen is taken from the rind of -a gourd. - -The “pitted” structure which is so well shown in this figure is caused -by a layer of matter which is deposited in the cell and thickens its -walls, and which is perforated with a number of very minute holes -called “pits.” This substance is called “secondary deposit.” That these -pits do not extend through the real cell-wall has already been shown -in Fig. 12. - -This secondary deposit assumes various forms. In some cases it is -deposited in rings round the cell, and is clearly placed there for -the purpose of strengthening the general structure. Such an example -may be found in the mistletoe (Fig. 5), where the secondary deposit -has formed itself into clear and bold rings that evidently give -considerable strength to the delicate walls which they support. Fig. 10 -shows another good instance of similar structure; differing from the -preceding specimen in being much longer and containing a greater number -of rings. This object is taken from an anther of the narcissus. Among -the many plants from which similar objects may be obtained, the yew is -perhaps one of the most prolific, as ringed wood-cells are abundant -in its formation, and probably aid greatly in giving to the wood the -strength and elasticity which have long made it so valuable in the -manufacture of bows. - -Before taking leave of the cells and their remarkable forms, we will -just notice one example which has been drawn in Fig. 6. This is a -congeries of cells, containing their nuclei, starting originally end to -end, but swelling and dividing at the top. This is a very young group -of cells (a young hair, in fact) from the inner part of a lilac bud, -and is here introduced for the purpose of showing the great similarity -of all vegetable cells in their earliest stages of existence. - -Having now examined the principal forms of cells, we arrive at the -“vessels,” a term which is applied to those long and delicate tubes -which are formed of a number of cells set end to end, their walls of -separation being absorbed. - -In Fig. 19 the reader will find a curious example of the “pitted -vessel,” so called from the multitude of little markings which cover -its walls, and are arranged in a spiral order. Like the pits and rings -already mentioned, the dots are composed of secondary deposit in the -interior of the tube, and vary very greatly in number, function, and -dimensions. This example is taken from the wood of the willow, and is -remarkable for the extreme closeness with which the dots are packed -together. - -Immediately on the right hand of the preceding figure may be seen -another example of a dotted vessel (Fig. 20), taken from a wheat stem. -In this instance the cells are not nearly so long, but are wider than -in the preceding example, and are marked in much the same way with a -spiral series of dots. About the middle of the topmost cell is shown -the short branch by which it communicates with the neighbouring vessel. - -Fig. 23 exhibits a vessel taken from the common carrot, in which the -secondary deposit is placed in such a manner as to resemble a net of -irregular meshes wrapped tightly round the vessel. For this reason -it is termed a “netted vessel.” A very curious instance of these -structures is given in Fig. 26, at the bottom of the Plate, where -are represented two small vessels from the wood of the elm. One of -them--that on the left hand--is wholly marked with spiral deposit, -the turns being complete; while, in the other instance, the spiral is -comparatively imperfect, and the cell-walls are marked with pits. If -the reader would like to examine these structures more attentively, he -will find plenty of them in many familiar garden vegetables, such as -the common radish, which is very prolific in these interesting portions -of vegetable nature. - -There is another remarkable form in which this secondary deposit is -sometimes arranged that is well worthy of our notice. An example -of this structure is given in Fig. 18, taken from the stalk of the -common fern or brake. It is also found in very great perfection in the -vine. On inspecting the illustration, the reader will observe that -the deposit is arranged in successive bars or steps, like those of a -winding staircase. In allusion to the ladder-like appearance of this -formation, it is called “scalariform” (Latin, _scala_, a ladder). - -In the wood of the yew, to which allusion has already been made, there -is a very peculiar structure, a series of pits found only in those -trees that bear cones, and therefore termed the coniferous pitted -structure. Fig. 16 is a section of a common cedar pencil, the wood, -however, not being that of the true cedar, but of a species of fragrant -Juniper. This specimen shows the peculiar formation which has just been -mentioned. - -Any piece of deal or pine will exhibit the same peculiarities in a -very marked manner, as is seen in Fig. 24. A specimen may be readily -obtained by making a very thin shaving with a sharp plane. In this -example the deposit has taken a partially spiral form, and the numerous -circular pits with which it is marked are only in single rows. In -several other specimens of coniferous woods, such as the Araucaria, or -Norfolk Island pine, there are two or three rows of pits. - -A peculiarly elegant example of this spiral deposit may be seen in the -wood of the common yew (Fig. 17). If an exceedingly thin section of -this wood be made, the very remarkable appearance will be shown which -is exhibited in the illustration. The deposit has not only assumed the -perfectly spiral form, but there are two complete spirals, arranged -at some little distance from each other, and producing a very pretty -effect when seen through a good lens. - -The pointed, elongated shape of the wood-cells is very well shown -in the common elder-tree (see Fig. 15). In this instance the cells -are without markings, but in general they are dotted like Fig. 21, -an example cut from the woody part of the chrysanthemum stalk. This -affords a very good instance of the wood-cell, as its length is -considerable, and both ends are perfect in shape. On the right hand -of the figure is a drawing of the wood-cell found in the lime-tree -(Fig. 22), remarkable for the extremely delicate spiral markings with -which it is adorned. In these wood-cells the secondary deposit is so -plentiful that the original membranous character of the cell-walls -is entirely lost, and they become elongated and nearly solid cases, -having but a very small cavity in their centre. It is to this deposit -that the hardness of wood is owing, and the reader will easily see -the reason why the old wood is so much harder than the young and new -shoots. In order to permit the passage of the fluids which maintain -the life of the part, it is needful that the cell-wall be left thin -and permeable in certain places, and this object is attained either -by the “pits” described on page <a href=\"#Page_43">43</a>, or by the -intervals between the spiral deposit. - -At the right-hand bottom corner of Plate I. (Fig. 28) may be seen -a prettily marked object, which is of some interest. It is a slice -stripped from the outer coat of the holly-berry, and is given for the -purpose of illustrating the method by which plants are enabled to -breathe the atmospheric air on which they depend as much as ourselves, -though their respiration is slower. Among the mass of net-like cells -may be seen three curious objects, bearing a rather close resemblance -to split kidneys. These are the mouths, or “stómata,” as they are -scientifically called. - -In the centre of the mouths may be seen a dark spot, which is the -aperture through which the air communicates with the passages between -the cells in the interior of the structure. In the flowering plants -their shape is generally rounded, though they sometimes take a squared -form, and they regularly occur at the meeting of several surface -cells. The two kidney-shaped cells which form the “mouth” are the -“guard-cells,” so called from their function, since, by their change of -form, they cause the mouth to open or shut, according to the needs of -the plant. In young plants these guard-cells are very little below the -surface of the leaf or skin, but in others they are sunk quite beneath -the layer of cells forming the outer coat of the tissue. There are -other cases where they are slightly elevated above the surface. - -Stomata are found chiefly in the green portions of plants, and are -most plentiful on the under side of leaves. It is, however, worthy of -notice, that when an aquatic leaf floats on the water, the mouths are -only to be found on the upper surface. These curious and interesting -objects are to be seen in many structures where we should hardly think -of looking for them; for instance, they may be found existing on the -delicate skin which envelops the kernel of the common walnut. As might -be expected, their dimensions vary with the character of the leaf on -which they exist, being large upon the soft and pulpy leaves, and -smaller upon those of a hard and leathery consistence. The reader will -find ample amusement, and will gain great practical knowledge of the -subject, by taking a plant, say a tuft of groundsel, and stripping off -portions of the external skin or “epidermis” from the leaf or stem, -etc., so as to note the different sizes and shapes of the stomata. - -On the opposite bottom corner of Plate I. Fig. 25, is an example of -a stoma taken from the outer skin of a gourd, and here given for the -purpose of showing the curious manner in which the cells are arranged -about the mouth, no less than seven cells being placed round the -single mouth, and the others arranged in a partially circular form -around them. - -Turning to Plate II., we find several other examples of stomata, the -first of which (Fig. 1) is obtained from the under surface of the -buttercup leaf, by stripping off the external skin, or “epidermis,” as -it is scientifically termed. The reader will here notice the slightly -waved outlines of the cell-walls, together with the abundant spots -of chlorophyll with which the leaf is coloured. In this example the -stomata appear open. Their closure or expansion depends chiefly on the -state of the weather; and, as a general rule, they are open by day and -closed at night. - -A remarkably pretty example of stomata and elongated cells is to be -obtained from the leaf of the common iris, and may be prepared for the -microscope by simply tearing off a strip of the epidermis from the -under side of the leaf, laying it on a slide, putting a little water on -it, and covering it with a piece of thin glass. (See Plate II. Fig. 2.) -There are a number of longitudinal bands running along the leaf where -these cells and stomata appear. The latter are not placed at regular -intervals, for it often happens that the whole field of the microscope -will be filled with cells without a single stoma, whilst elsewhere a -group of three or four may be seen clustered closely together. - -Fig. 3 on the same Plate exhibits a specimen of the beautifully waved -cells, without mouths, which are found on the upper surface of the ivy -leaf. These are difficult to arrange from the fresh leaf, but are -easily shown by steeping the leaf in water for some time, and then -tearing away the cuticle. The same process may be adopted with many -leaves and cuticles, and in some cases the immersion must be continued -for many days, and the process of decomposition aided by a very little -nitric acid in the water, or by boiling. - -On the same Plate are three examples of spiral and ringed vessels, -types of an endless variety of these beautiful and interesting -structures. Fig. 4 is a specimen of a spiral vessel taken from the -lily, and is a beautiful example of a double spire. The deposit which -forms this spiral is very strong, and it is to the vast number of -these vessels that the stalk owes its well-known elasticity. In many -cases the spiral vessels are sufficiently strong to be visible to the -naked eye, and to bear uncoiling. For example, if a leaf-stalk of -geranium be broken across, and the two fragments gently drawn asunder, -a great number of threads, drawn from the spiral vessels, will be seen -connecting the broken ends. In this case the delicate membranous walls -of the vessel are torn apart, and the stronger fibre which is coiled -spirally within it unrolls itself in proportion to the force employed. -In many cases these fibres are so strong that they will sustain the -weight of an inch or so of the stalk. - -In Fig. 5 is seen a still more bold and complex form of this curious -structure; being a coil of five threads, laid closely against each -other, and forming, while remaining in their natural position, an -almost continuous tube. This specimen is taken from the root of the -water lily, and requires some little care to exhibit its structure -properly. - -Every student of nature must be greatly struck with the analogies -between different portions of the visible creation. These spiral -structures which we have just examined are almost identical in -appearance, and to some extent in their function, with the threads that -are coiled within the breathing tubes of insects. This is in both cases -twofold, namely, to give support and elasticity to a delicate membrane, -and to preserve the tube in its proper form, despite the bending to -which it may be subjected. When we come to the anatomy of the insect in -a future page we shall see this structure further exemplified. - -In some cases the deposit, instead of forming a spiral coil, is -arranged in a series of rings, and the vessel is then termed -“annulated.” A very good example of this formation is given in Fig. 6, -which is a sketch of such a vessel, taken from a stalk of the common -rhubarb. To see these ringed vessels properly, the simplest plan is to -boil the rhubarb until it is quite soft, then to break down the pulpy -mass until it is flattened, to take some of the most promising portions -with the forceps, lay them on the slide and press them down with a thin -glass cover. They will not be found scattered at random through the -fibres, which elsewhere present only a congeries of elongated cells, -but are seen grouped together in bundles, and with a little trouble may -be well isolated, and the pulpy mass worked away so as to show them -in their full beauty. As may be seen in the illustration, the number -of the rings and their arrangement is extremely variable. A better, -but somewhat more troublesome, plan is to cut longitudinal sections of -the stem, as described in our concluding chapter, when not only the -various forms of cells and vessels, but their relations to each other, -will be well shown. The numerous crystals of oxalate of lime, which -make rhubarb so injurious a food for certain persons, will also be well -seen. These crystals are called “raphides,” and are to be found in very -many plants in different forms. - - -II. - - FIG. - 1. Cuticle, Buttercup leaf - 2. Do. Iris - 3. Do. Ivy leaf - 4. Spiral vessel, Lily - 5. Do. root, (rhizome) Water Lily - 6. Ringed vessel, Rhubarb - 7. Chaff, after burning - 8. Bifid hair, Arabis - 9. Hair, Marvel of Peru - 10. End of hair, leaf of Hollyhock - 11. Hair, Sowthistle leaf - 12. Do. Tobacco - 13. Do. Southernwood - 14. Group of hairs, Hollyhock leaf - 15. Hair, Yellow Snapdragon - 16. Do. Moneywort - 17. Hair, Geum - 18. Do. Flower of Heartsease - 19. Do. Dockleaf - 20. Do. Throat of Pansy - 21. Do. Dead-nettle Flower - 22. Do. Groundsel - 23. Cell, Beech-nut - 24. Do. Pine cone - 25. Vitta, Caraway Seed - 26. Cork - 27. Hair, Flower of Garden Verbena - 28. Do. fruit of Plane - 29. Do. do. - 30. Do. do. - 31. Do. Lobelia - 32. Do. Cabbage - 33. Do. Dead-nettle flower - 34. Do. Garden Verbena flower - 35. Fruit-hair, Dandelion - 36. Hair, Thistle leaf - 37. Do. Cactus - 38. Do. do. - 39. Do. Virginian Spider-wort - 40. Do. Lavender - 41. Section, Lavender leaf, Hairs and perfume-gland - 42. Section, Orange Peel - 43. Sting of Nettle - 44. Hair, Marigold flower - 45. Do. Ivy - -[Illustration: II.] - - * * * * * - -The hairs of plants form very interesting objects, and are instructive -to the student, as they afford valuable indications of the mode in -which plants grow. They are all appendages of and arise from the skin -or epidermis; and although their simplest form is that of a projecting -and elongated cell, the variety of shapes which are assumed by these -organs is inexhaustible. On Plate II. are examples of some of the more -striking forms, which will be briefly described. - -The simple hair is well shown in Figs. 18, 19, and 32, the first being -from the flower of the heartsease, the second from a dock-leaf, and the -third from a cabbage. In Fig. 18 the hair is seen to be but a single -projecting cell, consisting only of a wall and the contents. In Fig. 19 -the hair has become more decided in shape, having assumed a somewhat -dome-like form; and in Fig. 32 it has become considerably elongated, -and may at once be recognised as a true hair. - -In Fig. 8 is a curious example of a hair taken from the white Arabis, -one of the cruciferous flowers, which is remarkable for the manner -in which it divides into two branches, each spreading in opposite -directions. Another example of a forked hair is seen in Fig. 13, but in -this instance the hair is composed of a chain of cells, the three lower -forming the stem of the hair, and the two upper being lengthened into -the lateral branches. This hair is taken from the common southernwood. - -In most cases of long hairs, the peculiar elongation is formed by a -chain of cells, varying greatly in length and development. Several -examples of these hairs will be seen on the same Plate. - -Fig. 9 is a beaded hair from the Marvel of Peru, which is composed of -a number of separate cells placed end to end, and connected by slender -threads in a manner that strongly reminds the observer of a chain of -beads strung loosely together, so as to show the thread by which they -are connected with each other. Another good example is seen at Fig. 11, -in a hair taken from the leaf of the sowthistle. In this case the -beads are strung closely together, and when placed under a rather high -power of the microscope have a beautifully white and pearly aspect. -The leaf must be dry and quite fresh, and the hairs seen against the -green of the leaf. Fig. 39 represents another beaded hair taken from -the Virginian Spiderwort, or Tradescantia. This hair is found upon the -stamens, and is remarkable for the beautifully beaded outline, the -fine colouring, and the spiral markings with which each cell is adorned. - -A still further modification of these many-celled hairs is found in -several plants, where the hairs are formed by a row of ordinarily -shaped cells, with the exception of the topmost cell, which is suddenly -elongated into a whip-like form. Fig. 22 represents a hair of this -kind, taken from the common groundsel; and Fig. 36 is a still more -curious instance, found upon the leaf of the thistle. The reader may -have noticed the peculiar white “fluffy” appearance of the thistle leaf -when it is wet after a shower of rain. This appearance is produced -by the long lash-like ends of the hairs, which are bent down by the -weight of the moisture, and lie almost at right angles with the thicker -portions of the hair. - -An interesting form of hair is seen in the “sting” of the common -nettle. This may readily be examined by holding a leaf edgewise in the -stage forceps, and laying it under the field of the microscope. In -order to get the proper focus throughout the hair, the finger should -be kept upon the screw movement, and the hair brought gradually into -focus from its top to its base. The general structure of this hair is -not unlike that which characterises the fang of a venomous serpent. The -acrid fluid which causes the pain is situated in the enlarged base of -the hair, and is forced through the long straight tubular extremity by -means of the pressure exerted when the sting enters the skin. At the -very extremity of the perfect sting is a slight bulb-like swelling, -which serves to confine the acrid juice, and which is broken off on the -least pressure. The sting is seen in Fig. 43. - -The extremities of many hairs present very curious forms, some being -long and slender, as in the examples already mentioned, while others -are tipped with knobs, bulbs, clubs, or rosettes in endless variety. - -Fig. 12 is a hair of the tobacco leaf, exhibiting the two-celled gland -at the tip, containing the peculiar principle of the plant, known by -the name of “nicotine.” The reader will see how easy it is to detect -adulteration of tobacco by means of the microscope. The leaves most -generally used for this purpose are the dock and the cabbage, so that -if a very little portion of leaf be examined the character of the hairs -will at once inform the observer whether he is looking at the real -article or its substitute. - -Fig. 15 is a hair from the flower of the common yellow snapdragon, -which is remarkable for the peculiar shape of the enlarged extremity, -and for the spiral markings with which it is decorated. Fig. 16 is a -curious little knobbed hair found upon the moneywort, and Fig. 17 is an -example of a double-knobbed hair taken from the Geum. Fig. 34 affords -a very curious instance of a glandular hair, the stem being built up -of cells disposed in a very peculiar fashion, and the extremity being -developed into a beautiful rosette-shaped head. This hair came from -the Garden Verbena. - -Curiously branched hairs are not at all uncommon, and some very good -and easily obtained examples are given on Plate II. - -Fig. 28 is one of the multitude of branched hairs that surround the -well-known fruit of the plane-tree, the branches being formed by some -of the cells pointing outward. These hairs do not assume precisely the -same shape; for Fig. 29 exhibits another hair from the same locality, -on which the spikes are differently arranged, and Fig. 30 is a sketch -of another such hair, where the branches have become so numerous and so -well developed that they are quite as conspicuous as the parent stem. - -One of the most curious and interesting forms of hair is that which -is found upon the lavender leaf, and which gives it the peculiar -bloom-like appearance on the surface. - -This hair is represented in Figs. 40 and 41. On Fig. 40 the hair is -shown as it appears when looking directly upon the leaf, and in Fig. 41 -a section of the leaf is given, showing the mode in which the hairs -grow into an upright stem, and then throw out horizontal branches in -every direction. Between the two upright hairs, and sheltered under -their branches, may be seen a glandular appendage not unlike that which -is shown in Fig. 16. This is the reservoir containing the perfume, and -it is evidently placed under the spreading branches for the benefit -of their shelter. On looking upon the leaf by reflected light the -hairs are beautifully shown, extending their arms on all sides; and -the globular perfume cells may be seen scattered plentifully about, -gleaming like pearls through the hair-branches under which they repose. -They will be found more numerous on the under side of the leaf. - -This object will serve to answer a question which the reader has -probably put to himself ere this, namely, Where are the fragrant -resins, scents, and oils stored? On Plate I. Fig. 16, will be seen the -reply to the first question; Fig. 41 of the present Plate has answered -the second question, and Fig. 42 will answer the third. This figure -represents a section of the rind of an orange, the flattened cells -above constituting the delicate yellow skin, and the great spherical -object in the centre being the reservoir in which the fragrant -essential oil is stored. The covering is so delicate that it is easily -broken, so that even by handling an orange some of the scent is sure -to come off on the hands, and when the peel is stripped off and bent -double, the reservoirs burst in myriads, and fling their contents to -a wonderful distance. This may be easily seen by squeezing a piece of -orange peel opposite a lighted candle, and noting the distance over -which the oil will pass before reaching the flame, and bursting into -little flashes of light. Other examples are given on the same plate. - -Returning to the barbed hairs, we may see in Fig. 35 a highly magnified -view of the “pappus” hair of a dandelion, _i.e._ the hairs which -fringe the arms of the parachute-like appendage which is attached -to the seed. The whole apparatus will be seen more fully on Plate -III. Figs. 44, 45, 46. This hair is composed of a double layer of -elongated cells lying closely against each other, and having the ends -of each cell jutting out from the original line. A simpler form of -a double-celled, or more properly a “duplex” hair, will be seen in -Fig. 44. This is one of the hairs from the flower of the marigold and -has none of the projecting ends to the cells. - -In some instances the cell-walls of the hairs become greatly hardened -by secondary deposit, and the hairs are then known as spines. Two -examples of these are seen in Figs. 37 and 38, the former being picked -from the Indian fig-cactus, and well known to those persons who have -been foolish enough to handle the fig roughly before feeling it. The -wounds which these spines will inflict are said to be very painful, -and have been compared to those produced by the sting of the wasp. -The latter hair is taken from the Opuntia. These spines must not be -confounded with thorns; which latter are modified branches. - -Fig. 10 represents the extreme tip of a hair from the hollyhock leaf, -subjected to a lens of very high power. - -Many hairs assume a star-like appearance, an aspect which may be -produced in different ways. Sometimes a number of simple hairs start -from the same base, and by radiating in different directions produce -the stellate effect. An example of this kind of hair may be seen in -Fig. 14, which is a group of hairs from the hollyhock leaf. There is -another mode of producing the star-shape which may be seen in Fig. 45, -a hair taken from the leaf of the ivy. Very fine examples may also be -found upon the leaf of Deutzia scabra. - -Hairs are often covered with curious little branches or protuberances, -and present many other peculiarities of form which throw a considerable -light upon certain problems in scientific microscopy. - -Fig. 33 represents a hair of two cells taken from the flower of the -well-known dead-nettle, which is remarkable for the number of knobs -scattered over its surface. A similar mode of marking is seen in -Fig. 31, a club-shaped hair covered with external projections, found -in the flower of the Lobelia. In order to exhibit these markings well, -a power of two hundred diameters is needed. Fig. 21 shows this dotting -in another hair from the dead-nettle, where the cell is drawn out to a -great length, but is still covered with these markings. - -Fig. 20 is an example of a very curious hair taken from the throat of -the pansy. This hair may readily be obtained by pulling out one of the -petals, when the hairs will be seen at its base. Under the microscope -it has a particularly beautiful appearance, looking just like a glass -walking-stick covered with knobs, not unlike those huge, knobby -club-like sticks in which some farmers delight, where the projections -have been formed by the pressure of a honeysuckle or other climbing -plant. - -A hair of a similar character, but even more curious, is found in the -same part of the flower of the Garden Verbena (see Fig. 27), and is not -only beautifully translucent, but is coloured according to the tint of -the flower from which it is taken. Its whole length is covered with -large projections, the joints much resembling the antennæ of certain -insects; and each projection is profusely spotted with little dots, -formed by elevation of the outer skin or cuticle. These are of some -value in determining the structure of certain appearances upon petals -and other portions of the flowers, and may be compared with Figs. 33 to -35 on Plate III. - -Fig. 26 offers an example of the square cells which usually form the -bark of trees. This is a transverse section of cork, and perfectly -exhibits the form of bark cells. The reader is very strongly advised -to cut a delicate section of the bark of various trees, a matter very -easily accomplished with the aid of a sharp razor and a steady hand. - -Fig. 24 is a transverse section through one of the scales of a -pine-cone, and is here given for the purpose of showing the numerous -resin-filled cells which it displays. This may be compared with Fig. 16 -of Plate I. Fig. 25 is a part of one of the “vittæ,” or oil reservoirs, -from the fruit of the caraway, showing the cells containing the -globules of caraway oil. This is rather a curious object, because the -specimen from which it was taken was boiled in nitric acid, and yet -retained some of the oil globules. Immediately above it may be seen -(Fig. 23) a transverse section of the beechnut, showing a cell with -its layers of secondary deposit. - -In the cuticle of the grasses and the mare’s-tails is deposited a large -amount of pure flint. So plentiful is this substance, and so equally -is it distributed, that it can be separated by heat or acids from the -vegetable parts of the plant, and will still preserve the form of the -original cuticle, with its cell-walls, stomata, and hairs perfectly -well defined. - -Fig. 7, Plate II., represents a piece of wheat chaff, or “bran,” that -has been kept at a white heat for some time, and then mounted in -Canada balsam. I prepared the specimen from which the drawing was made -by laying the chaff on a piece of platinum, and holding it over the -spirit-lamp. A good example of the silex or flint in wheat is often -given by the remains of a straw fire, where the stems may be seen still -retaining their tubular form but fused together into a hard glassy -mass. It is this substance that cuts the fingers of those who handle -the wild grasses too roughly, the edges of the blades being serrated -with flinty teeth, just like the obsidian swords of the ancient -Mexicans, or the shark’s-tooth falchion of the New Zealander. - -These are but short and meagre accounts of a very few objects, but -space will not permit of further elucidation, and the purpose of this -little work is not to exhaust the subjects of which it treats, but to -incite the reader to undertake investigation on his own account, and to -make his task easier than if he had done it unaided. - - - - -CHAPTER V - - Starch, its Growth and Properties--Surface Cells of Petals--Pollen - and its Functions--Seeds. - - -The white substance so dear to the laundries under the name of starch -is found in a vast variety of plants, being distributed more widely -than most of the products which are found in the interior of vegetable -cells. - -The starch grains are of very variable size even in the same plant, -and their form is as variable as their size, though there is a general -resemblance in those of the same plant which allows of their being -fairly easily identified after a moderate amount of practice. Sometimes -the grains are found loosely packed in the interior of the cells, and -are then easily recognised as starch grains by their peculiar form -and the delicate lines with which they are marked; but in many places -they are pressed so closely together that they assume an hexagonal -shape under the microscope, and bear a close resemblance to ordinary -twelve-sided cells. In other plants, again, the grains never advance -beyond the very minute form in which they seem to commence their -existence; and in some, such as the common oat, a great number of very -little granules are compacted together so as to resemble one large -grain. - -There are several methods of detecting starch in those cases where -its presence is doubtful; and the two modes that are usually employed -are polarised light and the iodide of potassium. When polarised -light is employed--a subject on which we shall have something to say -presently--the starch grains assume the characteristic “black-cross,” -and when a plate of selenite is placed immediately beneath the slide -containing the starch grains, they glow with all the colours of the -rainbow. The second plan is to treat them with a very weak solution -of iodine and iodide of potassium, and in this case the iodine has -the effect on the starch granules of staining them blue. They are so -susceptible of this reaction that when the liquid is too strong the -grains actually become black from the amount of iodine which they -imbibe. - -Nothing is easier than to procure starch granules in the highest -perfection. Take a raw potato, and with a razor cut a very thin -slice from its interior, the direction of the cut not being of the -slightest importance. Put this delicate slice upon a slide, drop a -little water upon it, cover it with a piece of thin glass, give it a -good squeeze, and place it under a power of a hundred or a hundred and -fifty diameters. Any part of the slice, provided that it be very thin, -will then present the appearance shown in Plate III. Fig. 9, where an -ordinary cell of potato is seen filled loosely with starch grains of -different sizes. Around the edges of the slice a vast number of starch -granules will be seen, which have been squeezed out of their cells by -pressure, and are now floating freely in the water. As cold water has -no perceptible effect upon starch, the grains are not altered in form -by the moisture, and can be examined at leisure. - - -III. - - FIG. - 1. Laurel leaf, transverse section - 2. Starch, Wheat - 3. Do. from Pudding - 4. Do. Potato - 5. Outer Skin, Capsicum pod - 6. Starch, Parsnip - 7. Do. Arrow Root, West Indian - 8. Do. “Tousles Mois” - 9. Do. in cell of Potato - 10. Do. Indian Corn - 11. Do. Sago - 12. Do. Tapioca - 13. Root, Yellow Water-Lily - 14. Starch, Rice - 15. Do. Horsebean - 16. Do. Oat - 17. Pollen, Snowdrop - 18. Do. Wallflower - 19. Do. Willow Herb, a pollen tube - 20. Do. Violet - 21. Do. Musk Plant - 22. Do. Apple - 23. Do. Dandelion - 24. Do. Sowthistle - 25. Do. Lily - 26. Do. Heath - 27. Do. Heath, another species - 28. Pollen, Furze - 29. Do. Tulip - 30. Petal, Pelargonium - 31. Do. Periwinkle - 32. Do. Golden Balsam - 33. Do. Snapdragon - 34. Do. Primrose - 35. Do. Scarlet Geranium - 36. Pollen, Crocus - 37. Do. Hollyhock - 38. Fruit, Galium, Goosegrass - 39. A hook of ditto more magnified - 40. Seed, Red Valerian - 41. Portion of Parachute of same, more magnified - 42. Seed, Foxglove - 43. Do. Sunspurge - 44. Parachute, Dandelion seed - 45. Seed, Dandelion - 46. Do. Hair of Parachute - 47. Do. Yellow Snapdragon - 48. Do. Mullein - 49. Do. Robin Hood - 50. Do. Bur-reed - 51. Do. Willow Herb - 52. Do. Musk Mallow - -[Illustration: III.] - -On focusing with great care, the surface of each granule will be seen -to be covered with very minute dark lines, arranged in a manner which -can be readily comprehended from Fig. 4, which represents two granules -of potato starch as they appear when removed from the cell in which -they took their origin. All the lines evidently refer to the little -dark spots at the end of the granule, called technically the “hilum,” -and represent the limits of successive layers of material deposited -one after another. The lines in question are very much better seen if -the substage condenser be used with a small central stop, so as to -obtain partial dark-field illumination. Otherwise they are often very -difficult of detection. - -In the earliest stages of their growth the starch granules appear to be -destitute of these markings, or at all events they are so few and so -delicate as not to be visible even with the most perfect instruments, -and it is not until the granules assume a comparatively large size that -the external markings become distinctly perceptible. - -We will now glance at the examples of starch which are given in the -Plate, and which are a very few out of the many that might be figured. -Fig. 2 represents the starch of wheat, the upper grain being seen in -front, the one immediately below it in profile, and the two others -being examples of smaller grains. Fig. 6 is a specimen of a very minute -form of starch, where the granules do not seem to advance beyond -their earliest stage. This specimen is obtained from the parsnip; and -although the magnifying power is very great, the dimensions of the -granules are exceedingly small, and except by a very practised eye they -would not be recognisable as starch grains. - -Fig. 3 is a good example of a starch grain of wheat, exemplifying the -change that takes place by the combined effects of heat and moisture. -It has already been observed that cold water exercises little, if -any, perceptible influence upon starch; but it will be seen from -the illustration that hot water has a very powerful effect. When -subjected to the action of water at a temperature over 140° Fahr., -the granule swells rapidly, and at last bursts, the contents escaping -in a gelatinous mass, and the external membrane collapsing into the -form which is shown in Fig. 3, which was taken out of a piece of hot -pudding. A similar form of wheat starch may also be detected in bread, -accompanied, unfortunately, by several other substances not generally -presumed to be component parts of the “staff of life.” - -In Fig. 7 are represented some grains of starch from West Indian -arrowroot, and Fig. 8 exhibits the largest kind of starch grain known, -obtained from the tuber of a species of canna, supposed to be _C. -edúlis_, a plant similar in characteristics to the arrowroot. The -popular name of this starch is “Tous les Mois,” and under that title -it may be obtained from the opticians, or chemists. - -Fig. 10 shows the starch granules from Indian corn, as they appear -before they are compressed into the honeycomb-like structure which -has already been mentioned. Even in that state, however, if they are -treated with iodine, they exhibit the characteristics of starch in a -very perfect manner. Fig. 11 is starch from sago, and Fig. 12 from -tapioca, and in both these instances the several grains have been -injured by the heat employed in preparing the respective substances for -the market. - -Fig. 13 exhibits the granules obtained from the root of the water-lily, -and Fig. 14 is a good example of the manner in which the starch -granules of rice are pressed together so as to alter the shape and -puzzle a novice. Fig. 16 is the compound granule of the oat, which -has already been mentioned, together with some of the simple granules -separated from the mass; and Fig. 15 is an example of the starch grains -obtained from the underground stem of the horse-bean. It is worthy of -mention that the close adhesion of the rice starch into those masses is -the cause of the peculiar grittiness which distinguishes rice flour to -the touch. - -Whilst very easily acted on by heat, starch-granules are very resistent -to certain other reagents. Weak alkalies, in watery solution, readily -attack them, but by treating portions of plants with caustic potash -dissolved in strong spirit, the woody and other parts may be dissolved -away; and after repeated washing with spirit the starch may be mounted. -This, however, must never be in any glycerine medium, except that given -on p. <a href=\"#Page_172">172</a>. - - * * * * * - -In Plate III. Fig. 1, may be seen a curious little drawing, which is -a sketch of the laurel-leaf cut transversely, and showing the entire -thickness of the leaf. Along the top may be seen the delicate layer -of “varnish” with which the surface of the leaf is covered, and which -serves to give to the foliage its peculiar polish. This varnish is -nothing more than the translucent matter which binds all the cells -together, and which is poured out very liberally upon the surface of -the leaf. The lower part of this section exhibits the cells of which -the leaf is built, and towards the left hand may be seen a cut end of -one of the veins of the leaf, more rightly called a wood-cell. - -We will now examine a few examples of surface cells. - -Fig. 5 is a portion of epidermis stripped from a Capsicum pod, -exhibiting the remains of the nuclei in the centre of each cell, -together with the great thickening of the wall-cells and the numerous -pores for the transmission of fluid. This is a very pretty specimen for -the microscope, as it retains its bright red colour, and even in old -and dried pods exhibits the characteristic markings. - -In the centre of the Plate may be seen a wheel-like arrangement of -the peculiar cells found on the petals of six different flowers, all -easily obtainable, and mounted without difficulty. - -Fig. 30 is the petal of a geranium (Pelargonium), a very common object -on purchased slides. It is a most lovely subject for the microscope, -whether it be examined with a low or a high power,--in the former -instance exhibiting a most beautiful “stippling” of pink, white, and -black, and in the latter showing the six-sided cells with their curious -markings. - -In the centre of each cell is seen a radiating arrangement of dark -lines with a light spot in the middle, looking very like the mountains -on a map. These lines were long thought to be hairs; but Mr. Tuffen -West, in an interesting and elaborate paper on the subject, has shown -their true nature. From his observations it seems that the beautiful -velvety aspect of flower petals is owing to these arrangements of the -surface cells, and that their rich brilliancy of colour is due to the -same cause. The centre of each cell-wall is elevated as if pushed up by -a pointed instrument from the under side of the wall, and in different -flowers this elevation assumes different forms. Sometimes it is merely -a slight wart on the surface, sometimes it becomes a dome, while in -other instances it is so developed as to resemble a hair. Indeed, -Mr. West has concluded that these elevations are nothing more than -rudimentary hairs. - -The dark radiating lines are shown by the same authority to be formed -by wrinkling of the membrane forming the walls of the elevated centre, -and not to be composed of “secondary deposit,” as has generally been -supposed. - -Fig. 31 represents the petal of the common periwinkle, differing from -that of the geranium by the straight sides of the cell-walls, which do -not present the toothed appearance so conspicuous in the former flower. -A number of little tooth-like projections may be seen on the interior -of the cells, their bases affixed to the walls and their points tending -toward the centre, and these teeth are, according to Mr. West, formed -of secondary deposit. - -In Fig. 32 is shown the petal of the common garden balsam, where the -cells are elegantly waved on their outlines, and have plain walls. -The petal of the primrose is seen in Fig. 34, and that of the yellow -snapdragon in Fig. 33; in the latter instance the surface cells assume -a most remarkable shape, running out into a variety of zigzag outlines -that quite bewilders the eye when the object is first placed under the -microscope. Fig. 35 is the petal of the common scarlet geranium. - -In several instances these petals are too thick to be examined without -some preparation, and glycerine will be found well adapted for that -purpose. The young microscopist must, however, beware of forming his -ideas from preparations of dried leaves, petals, or hairs, and should -always procure them in their fresh state whenever he desires to make -out their structure. Even a fading petal should not be used, and if the -flowers are gathered for the occasion, their stalks should be placed -in water, so as to give a series of leaves and petals as fresh as -possible. - - * * * * * - -We now pass from the petal of the flower to the pollen, that coloured -dust, generally yellow or white, which is found upon the stamens, and -which is very plentiful in many flowers, such as the lily and the -hollyhock. - -This substance is found only upon the stamens or anthers of full-blown -flowers (the anthers being the male organs), and is intended for the -purpose of enabling the female portion of the flower to produce fertile -seeds. In form the pollen grains are wonderfully diverse, affording -an endless variety of beautiful shapes. In some cases the exterior is -smooth and marked only with minute dots, but in many instances the -outer wall of the pollen grain is covered with spikes, or decorated -with stripes or belts. A few examples of the commonest forms of pollen -will be found on Plate III. - -Fig. 17 is the pollen of the snowdrop, which, as will be seen, is -covered with dots and marked with a definite slit along its length. -The dots are simply tubercles in the outer coat of the grain, and -are presumed to be formed for the purpose of strengthening the -membrane, otherwise too delicate, upon the same principle which gives -to “corrugated” iron such strength in proportion to the amount of -material. Fig. 18 is the pollen of the wall-flower, shown in two views, -and having many of the same characteristics as that of the snowdrop. -Fig. 19 is the pollen of the willow-herb, and is here given as an -illustration of the manner in which the pollen aids in the germination -of plants. - -In order to understand its action, we must first examine its structure. - -All pollen-grains are furnished with some means by which their contents -when thoroughly ripened can be expelled. In some cases this end is -accomplished by sundry little holes called pores; in others, certain -tiny lids are pushed up by the contained matter; and in some, as in -the present instance, the walls are thinned in certain places so as to -yield to the internal pressure. - -When a ripe pollen-grain falls upon the stigma of a flower, it -immediately begins to swell, and seems to “sprout” like a potato in -a damp cellar, sending out a slender “pollen-tube” from one or other -of the apertures already mentioned. In Fig. 19 a pollen-tube is seen -issuing from one of the projections, and illustrates the process better -than can be achieved by mere verbal description. The pollen-tubes -insinuate themselves between the cells of the stigmas, and, continually -elongating, worm their way down the “style” until they come in contact -with the “ovules.” By very careful dissection of a fertilised stigma, -the beautiful sight of the pollen-tubes winding along the tissues of -the style may be observed under a high power of the microscope. - -The pollen-tube is nothing more than the interior coat of the grain, -very much developed, and filled with a substance technically named -“fovilla,” composed of “protoplasm” (the semi-liquid substance which -is found in the interior of cells), very minute starch grains, and some -apparently oily globules. - -In order to examine the structure of the pollen-grains properly, they -should be examined under various circumstances--some dry, others placed -in water to which a little sugar has been added, others in oil, and it -will often be found useful to try the effect of different acids upon -them. - -Fig. 20 is the pollen of the common violet, and is easily recognisable -by its peculiar shape and markings. Fig. 21 is the pollen of the -musk-plant, and is notable for the curious mode in which its surface -is belted with wide and deep bands, running spirally round the -circumference. Fig. 22 exhibits the pollen of the apple, and Fig. 23 -affords a very curious example of the raised markings upon the surface -of the dandelion pollen. In Fig. 24 there are also some very wonderful -markings, but they are disposed after a different fashion, forming a -sort of network upon the surface, and leaving several large free spaces -between the meshes. The pollen of the lily is shown in Fig. 25, and is -a good example of a pollen-grain covered with the minute dottings which -have already been described. - -Figs. 26 and 27 show two varieties of compound pollen, found in two -species of heath. These compound pollen-grains are not of unfrequent -occurrence, and are accounted for in the following manner. - -The pollen is formed in certain cavities within the anthers, by means -of the continual subdivision of the “parent-cells” from which it is -developed. In many cases the form of the grain is clearly owing to the -direction in which these cells have divided, but there is no great -certainty on this subject. It will be seen, therefore, that if the -process of subdivision be suddenly arrested, the grains will be found -adhering to each other in groups of greater or smaller size, according -to the character of the species and the amount of subdivision that has -taken place. The reader must, however, bear in mind that the whole -subject is as yet rather obscure, and that further discovery may throw -doubt on many theories which at present are accepted as established. - -Fig. 28 shows the pollen of the furze, in which are seen the -longitudinal slits and the numerous dots on the surface; and Fig. 29 -is the curiously shaped pollen of the tulip. The two large yellow -globular figures at each side of the Plate represent the pollen of -two common flowers; Fig. 36 being that of the crocus, and Fig. 37 a -pollen-grain of the hollyhock. As may be seen from the illustration, -the latter is of considerable size, and is covered with very numerous -projections. These serve to raise the grain from a level surface, over -which it rolls with a surprising ease of motion, so much so indeed -that if a little of this substance be placed on a slide and a piece -of thin glass laid over it, the glass slips off as soon as it is in -the least inclined, and forces the observer to fix it with paper or -cement before he can place it on the inclined stage of the microscope. -The little projections have a very curious effect under a high -power, and require careful focusing to observe them properly; for the -diameter of the grain is so large that the focus must be altered to -suit each individual projection. Their office is, probably, to aid in -fertilisation. - - * * * * * - -The seeds of plants are even easier of examination than the pollen, and -in most cases require nothing but a pocket lens and a needle for making -out their general structure. The smaller seeds, however, must be placed -under the microscope, many of them exhibiting very curious forms. The -external coat of seeds is often of great interest, and needs to be -dissected off before it can be rightly examined. The simplest plan in -such a case is to boil the seed well, press it while still warm into -a plate of wax, and then dissect with a pair of needles, forceps, and -scissors under water. Many seeds may also be mounted in cells as dry -objects, after being thoroughly dried themselves. - -A few examples of the seeds of common plants are given at the bottom of -Plate III. - -Fig. 38 exhibits the fruit, popularly called the seed, of the common -goosegrass, or Galium, which is remarkable for the array of hooklets -with which it is covered. Immediately above the figure may be seen a -drawing of one of the hooks much magnified, showing its sharp curve -(Fig. 39). It is worthy of remark that the hook is not a simple curved -hair, but a structure composed of a number of cells terminating in a -hook. - -Fig. 40 shows the seed, or rather the fruit, of the common red -valerian, and is introduced for the purpose of showing its plumed -extremity, which acts as a parachute, and causes it to be carried -about by the wind until it meets with a proper resting-place. It is -also notable for the series of strong longitudinal ribs which support -its external structure. On Fig. 41 is shown a portion of one of the -parachute hairs much more magnified. - -The seed of the common dandelion, so dear to children in their -play-hours, when they amuse themselves by puffing at the white -plumy globes which tip the ripe dandelion flower-stalks, is a very -interesting object even to their parents, on account of its beautiful -structure, and the wonderful way in which it is adapted to the place -which it fills. Fig. 45 represents the seed portion of one of these -objects, together with a part of the parachute stem, the remainder of -that appendage being shown lying across the broken stem. - -The shape of the seed is not unlike that of the valerian, but it is -easily distinguished from that object by the series of sharp spikes -which fringe its upper end, and which serve to anchor the seed firmly -as soon as it touches the ground. From this end of the seed proceeds -a long slender shaft, crowned at its summit by a radiating plume of -delicate hairs, each of which is plentifully jagged on its surface, as -may be seen in Fig. 46, which shows a small portion of one of these -hairs greatly magnified. These jagged points are evidently intended to -serve the same purpose as the spikes below, and to arrest the progress -of the seed as soon as it has found a convenient spot. - -Fig. 42 is the seed of the foxglove, and Fig. 43 the seed of the -sunspurge, or milkwort. Fig. 47 shows the seed of the yellow -snapdragon; remarkable for the membranous wing with which the seed -is surrounded, and which is composed of cells with partially spiral -markings. When viewed edgewise, it looks something like Saturn with -his ring, or, to use a more homely but perhaps a more intelligible -simile, like a marble set in the middle of a penny. Fig. 48 is a seed -of mullein, covered with net-like markings on its external surface. -These are probably to increase the strength of the external coat, and -are generally found in the more minute seeds. - -On Fig. 50 is shown a seed of the burr-reed; a structure which is -remarkable for the extraordinary projection of the four outer ribs, and -their powerful armature of reverted barbs. Fig. 51 shows another form -of parachute seed, found in the willow-herb, where the parachute is -not expanded nearly so widely as that of the valerian; neither is it -set upon a long slender stem like that of the dandelion, but proceeds -at once from the top of the seed, widening towards the extremity, -and having a very comet-like appearance. Two more seeds only remain, -Fig. 49 being the seed of Robin Hood, and the other, Fig. 52, that of -the muskmallow, being given in consequence of the thick coat of hairs -with which it is covered. - -Many seeds can be well examined when mounted in Canada balsam. - - - - -CHAPTER VI - - Algæ and their Growth--Desmidiaceæ, where found--Diatoms, their - Flinty Deposit--Volvox--Mould, Blight, and Mildew--Mosses and - Ferns--Mare’s-Tail and the Spores--Common Sea-weeds and their Growth. - - -On Plate IV. will be seen many examples of the curious vegetables -called respectively algæ and fungi, which exhibit some of the lowest -forms of vegetable life, and are remarkable for their almost universal -presence in all parts of this globe, and also almost all conditions of -cold, heat, or climate. Many of them are well known under the popular -name of sea-weeds, others are equally familiar under the titles of -“mould,” “blight,” or “mildew,” while many of the minuter kinds exhibit -such capability of motion, and such apparent symptoms of volition, that -they have long been described as microscopic animalcules, and thought -to belong to the animal rather than to the vegetable kingdoms. - -Fig. 1 represents one of the very lowest forms of vegetable life, being -known to the man of science as the Palmella, and to the general public -as “gory dew.” It may be seen on almost any damp wall, extending in red -patches of various sizes, looking just as if some blood had been dashed -on the wall, and allowed to dry there. With a tolerably powerful -lens this substance can be resolved into the exceedingly minute cells -depicted in the figure. Generally, these cells are single, but in many -instances they are double, owing to the process of subdivision by which -the plant grows, if such a term may be used. - -Fig. 2 affords an example of another very low form of vegetable, the -Palmoglæa, that green slimy substance which is so common on damp -stones. When placed under the microscope, this plant is resolvable -into a multitude of green cells, each being surrounded with a kind of -gelatinous substance. The mode of growth of this plant is very simple. -A line appears across one of the cells, and after a while it assumes a -kind of hour-glass aspect, as if a string had been tied tightly round -its middle. By degrees the cell fairly divides into two parts, and then -each part becomes surrounded with its own layer of gelatine, so as to -form two separate cells, placed end to end. - -One of the figures, that on the right hand, represents the various -processes of “conjugation,” _i.e._ the union and fusion together of two -cells. Each cell throws out a little projection; these meet together, -and then uniting, form a sort of isthmus connecting the two main -bodies. This rapidly widens, until the two cells become fused into one -large body. The whole subject of conjugation is very interesting, and -is treated at great length in the _Micrographic Dictionary_ of Messrs. -Griffith and Henfrey, a work to which the reader is referred for -further information on many of the subjects that, in this small work, -can receive but a very hasty treatment. - -Few persons would suppose that the slug-like object on Fig. 3, the -little rounded globules with a pair of hair-like appendages, and the -round disc with a dark centre, are only different forms of the same -organism. Such, however, is the case, and these are three of the -modifications which the Protococcus undergoes. This vegetable may be -seen floating like green froth on the surface of rain-water. - -On collecting some of this froth and putting it under the microscope, -it is seen to consist of a vast number of little green bodies, moving -briskly about in all directions, and guiding their course with such -apparent exercise of volition that they might very readily be taken for -animals. It may be noticed that the colour of the plant is sometimes -red, and in that state it has been called the Hæmatococcus. - -The “still” state of this plant is shown in the round disc. After a -while the interior substance splits into two portions; these again -subdivide, and the process is repeated until sixteen or thirty-two -cells become developed out of the single parent-cell. These little ones -then escape, and, being furnished with two long “cilia” or thread-like -appendages, whirl themselves merrily through the water. When they have -spent some time in this state, growing all the while, they lose their -cilia, become clothed with a strong envelope, and pass into the still -stage from which they had previously emerged. This curious process is -repeated in endless succession, and causes a very rapid growth of the -plant. The moving bodies are technically called zoospores, or living -spores, and are found in many other plants besides those of the lowest -order. - - -IV. - - FIG. - 1. Gory Dew, Palmella cruenta - 2. Palmoglæa macrococca - 3. Protococcus pluvialis, - _a_, in its motile, - _b_, in its fixed state, - _c_, zoospores - 4. Closterium - 5. Ditto, end more magnified - 6. Pediastrum - 7. Scenedesmus - 8. Oscillatoria - 9. Spirogyra - 10. Tyndaridea - 11. Do. spore - 12. Sphærozosma - 13. Chlorococcus - 14. Scenedesmus - 15. Pediastrum, to show cells - 16. Ankistrodesmus - 17. Cosmarium - 18. Desmidium - 19. Cosmarium, formation of Resting Spore - 20. Cocconema lanceolatum - 21. Diatoma vulgare - Do. larger frustules, at the side - 22. Volvox globator - Do. single green body, above - 23. Synedra - 24. Gomphonema acuminatum - Do. larger frustules, below - 25. Yeast - 26. Sarcina ventriculi - 27. Eunotia diadema - 28. Melosira varians - Do. two bleached frustules - 29. Cocconeis pediculus - 30. Achnanthes exilis - 31. Navicula amphisbœna - 32. Uredo, “Red-rust” of corn - 33. Puccinea, Mildew of corn - 34. Botrytis, mould on grapes - Do. Sporules, beside it - 35. Do. parasitica, Potato blight - 36. Ectocarpus siliculosus - 37. Ulva latissima - 38. Polypodium - Do. single spore, below - 39. Moss capsule, Hypnum - 40. Mare’s tail, Equisetum, _a_ - Do. do. _b_ and _c_ - 41. Porphyra laciniata - -[Illustration: IV.] - -On Fig. 13 is delineated a very minute plant, called from its colour -Chlorococcus. It may be found upon tree-trunks, walls, etc., in the -form of green dust, and has recently been found to take part in forming -the first stage of lichens. - -A large and interesting family of the “confervoid algæ,” as these low -forms of vegetable life are termed, is the Desmidiaceæ, called in more -common parlance desmids. A few examples of this family are given in -Plate IV. - -They may be found in water, always preferring the cleanest and the -brightest pools, mostly congregating in masses of green film at the -bottom of the water, or investing the stems of plants. Their removal -is not very easy, but is best accomplished by very carefully taking up -this green slippery substance in a spoon, and straining the water away -through fine muslin. They may also be separated by allowing a ring, -covered with muslin, to float upon the surface of the water collected -in a jar, for, being great lovers of light, they assemble where it -is most abundant. An opaque jar should be used. For preservation, -glycerine-gelatine seems to be the best fluid. A very full and accurate -description of these plants may be found in Ralfs’ _British Desmidieæ_. - -Fig. 4 represents one of the species of Closterium, more than twenty -of which are known. These beautiful objects can be obtained from the -bottom of almost every clear pool, and are of some interest on account -of the circulating currents that may be seen within the living plants. -A high power is required to see this phenomenon clearly. The Closteria -are reproduced in various ways. Mostly they divide across the centre, -being joined for a while by two half-cells. Sometimes they reproduce -by means of conjugation, the process being almost entirely conducted -on the convex sides. Fig. 5 represents the end of a Closterium, much -magnified in order to show the actively moving bodies contained within -it. - -Fig. 16 is a supposed desmid, called Ankistrodesmus, and presumed to be -an earlier stage of Closterium. - -Fig. 6 is a very pretty desmid called the Pediastrum, and valuable to -the microscopist as exhibiting a curious mode of reproduction. The -figure shows a perfect plant composed of a number of cells arranged -systematically in a star-like shape; Fig. 15 is the same species -without the colouring matter, in order to show the shape of the cells. -The Pediastrum reproduces by continual subdivision of the contents of -each cell into a number of smaller cells, termed “gonidia” on account -of their function on the perpetuation of the species. When a sufficient -number has been formed, they burst through the envelope of the original -cell, taking with them a portion of its internal layer, so as to form -a vesicle, in which they move actively. In a few minutes they arrange -themselves in a circle, and after a while they gradually assume the -perfect form, the whole process occupying about two days. Fig. 18 -exhibits an example of the genus Desmidium. In this genus the cells are -either square or triangular in their form, having two teeth at their -angles, and twisted regularly throughout their length, causing the wavy -or oblique lines which distinguish them. The plants of this genus are -common, and may be found almost in any water. I may as well mention -that I have obtained nearly all the preceding species, together with -many others, from a little pond on Blackheath. - -Fig. 7 is another desmid called Scenedesmus, in which the cells are -arranged in rows of from two to ten in number, the cell at each -extremity being often furnished with a pair of bristle-like appendages. -Fig. 14 is another species of the same plant, and both may be found in -the water supplied for drinking in London, as well as in any pond. - -A common species of desmid is seen at Fig. 12, called Sphærozosma, -looking much like a row of stomata set chainwise together. It -multiplies by self-division. - -Fig. 17 is a specimen of desmid named Cosmarium, plentifully found -in ponds on heaths and commons, and having a very pretty appearance -in the microscope, with its glittering green centre and beautifully -transparent envelope. The manner in which the Cosmarium conjugates is -very remarkable, and is shown at Fig. 19. - -The two conjugating cells become very deeply cleft, and by degrees -separate, suffering the contents to pour out freely, and, as at present -appears, without any envelope to protect them. The mass, however, -soon acquires an envelope of its own, and by degrees assumes a dark -reddish-brown tint. It is now termed a sporangium, and is covered with -a vast number of projections, which in this genus are forked at their -tip, but in others, which also form sporangia, are simply pointed. The -Closteria conjugate after a somewhat similar manner, and it is not -unfrequent to find a pair in this condition, but in their case the -sporangium is quite smooth on its surface. - -Another very remarkable family of confervoid algæ is that which is -known under the name of Oscillatoriæ, from the oscillating movement -of the plant. They are always long and filamentous in character, and -may be seen moving up and down with a curious irregularity of motion. -Their growth is extremely rapid, and may be watched under a tolerably -powerful lens, thus giving many valuable hints as to the mode by -which these plants are reproduced. One of the commonest species is -represented at Fig. 8. - -Figs. 9, 10, and 11 are examples of another family, called technically -the Zygnemaceæ, because they are so constantly yoked together by -conjugation. They all consist of a series of cylindrical cells, set end -to end, and having their green contents arranged in similar patterns. -Two of the most common and typical species are here given. - -Fig. 9 is the Spirogyra, so called from the spiral arrangement of -the chlorophyll; and Fig. 10 is the Tyndaridea, or Zygnema, as it is -called by some writers. A casual inspection will show how easy it is -to distinguish the one from the other. Fig. 11 represents a portion of -the Tyndaridea during the process of conjugation, showing the tube of -connection between the cells and one of the spores. - - * * * * * - -We now arrive at the diatoms, so called because of their method of -reproduction, in which it appears as if a cut were made right along the -original cell. The commonest of these plants is the Diatóma vulgáre, -seen in Fig. 21 as it appears while growing. The reproduction of this -plant is effected by splitting down the centre, each half increasing -to the full size of the original cell; and in almost every specimen of -water taken from a pond, examples of this diatom undergoing the process -of division will be distinguished. It also grows by conjugation. The -diatoms are remarkable for the delicate shell or flinty matter which -forms the cell skeleton, and which will retain its shape even after -intense heat and the action of nitric acid. While the diatoms are -alive, swimming through the water, their beautiful markings are clearly -distinct, glittering as if the form were spun from crystalline glass. -Just above the figure, and to the right hand, are two outlines of -single cells of this diatom, the one showing the front view and the -other the profile. - -Fig. 20 is an example of a diatom--Cocconéma lanceolátum--furnished -with a stalk. The left-hand branch sustains a “frustule” exhibiting the -front view, while the other is seen sideways. - -Another common diatom is shown in Fig. 23, and is known by the name of -Synedra. This constitutes a very large genus, containing about seventy -known species. In this genus the frustules are at first arranged upon -a sort of cushion, but in course of time they mostly break away from -their attachment. In some species they radiate in every direction from -the cushion, like the spikes of the ancient cavalier’s mace. - -Fig. 24 is another stalked diatom called Gomphonéma acuminátum, found -commonly in ponds and ditches. There are nearly forty species belonging -to this genus. A pair of frustules are also shown which exhibit the -beautiful flinty outline without the coloured contents (technically -called endochrome). - -Fig. 27 is a side view of a beautiful diatom, called Eunótia diadéma -from its diadem-like form. There are many species of this genus. When -seen upon the upper surface, it looks at first sight like a mere row of -cells with a band running along them; but by careful arrangement of the -light its true form may easily be made out. - -Fig. 28 represents a very common fresh-water diatom, named Melosíra -várians. The plants of this genus look like a cylindrical rod composed -of a variable number of segments, mostly cylindrical, but sometimes -disc-shaped or rounded. An end view of one of the frustules is seen -at the left hand, still coloured with its dots of “endochrome,” and -showing the cylindrical shape. Immediately above is a figure of another -frustule seen under both aspects with the endochrome removed. - -A rather curious species of diatom, called Cocconeïs pedículus, is -seen at Fig. 29 as it appears on the surface of common water-cress. -Sometimes the frustules, which in all cases are single, are crowded -very closely upon each other and almost wholly hide the substance on -which they repose. Fig. 30 is another diatom of a flag-like shape, -named Achnanthes, having a long slender filament attached to one end -of the lower frustule, representing the flag-staff. There are many -wonderful species of such diatoms, some running almost end to end like -a bundle of sticks, and therefore called Bacillária; others spreading -out like a number of fans, such as the genus Licmophora; while some -assume a beautiful wheel-like aspect, of which the genus Meridion -affords an excellent example. - -A very remarkable, and not uncommon, fresh-water diatom is the -Bacillária paradóxa. It looks, when at rest, like a broad brown ribbon -of varying length. The diatoms lie across the ribbon, on edge, and -slide upon each other exactly like the ladders of a fire-escape, so -that the broad ribbon is converted into a fine long thread, which -speedily closes up again into the original ribbon, and so _da capo_. -The reason for this movement, and how it is effected, is absolutely -unknown; indeed, nothing certain is known as to the way in which -diatoms move, nor has ever a probable guess yet been made. - -The last of the diatoms which we shall be able to mention in this -work is that represented on Fig. 31. The members of this genus have -the name of Navícula, on account of their boat-like shape and their -habit of gliding through the water in a canoe-like fashion. There are -many species of this genus, all of which are notable for the graceful -and varied courses formed by their outlines, and the extreme delicacy -of their markings. In many species the markings are so extremely -minute that they can only be made out with the highest powers of the -microscope and the most careful illumination, so that they serve as -test objects whereby the performance of a microscope can be judged by a -practical man. - - * * * * * - -The large spherical figure in the centre of Plate IV. represents an -example of a family belonging to the confervoid algæ, and known by the -name of Volvox globator. There seems to be but one species known. - -This singular plant has been greatly bandied about between the -vegetable and animal kingdoms, but seems now to be satisfactorily -settled among the vegetables. In the summer it may be found in pools -of water, sufficiently large to be visible to the naked eye, like a -little green speck proceeding slowly through the water. When a moderate -power is used, it appears as shown in the figure, and always contains -within its body a number of smaller individuals, which after a while -burst through the envelope of the parent and start upon an independent -existence. On a closer examination, a further generation may be -discovered even within the bodies of the children. The whole surface is -profusely covered with little green bodies, each being furnished with -a pair of movable cilia, by means of which the whole organism is moved -through the water. These bodies are analogous to the zoospores already -mentioned, and are connected with each other by a network of filaments. -Reproduction also takes place by conjugation as in other algæ. A -more magnified representation of one of the green bodies is shown -immediately above the larger figure. The volvox is apt to die soon when -confined in a bottle. - -Fig. 25 is the common yeast-plant, consisting simply of a chain of -cells, which increase by budding, and only form spores when they have -exhausted the nutriment in the fluid in which they live. Fig. 26 is -a curious object, whose scientific name is Sárcina ventrículi. It is -found in the human stomach. Similar forms are often to be found in the -air; for instance, a piece of cocoa-nut will exhibit this, and many -other kinds of Bacteria and moulds, after a few days’ exposure to the -air, preferably in a dark cupboard. - -We now come upon a few of the blights and mildews. A very interesting -series of forms is first to be alluded to. Upon the bramble-leaf may -often be found spots, at first red, then orange, then reddish black. -These are known as Œcidium berberidis. Fig. 32 shows the “red-rust” -of wheat, the Urédo; and Fig. 33 is the mildew of corn, known as -Puccinia. The interest lies in the fact that these three forms are -successive stages in the life-history of the same plant. Another -species of Urédo, together with a Phragmídium, once thought to be -another kind of fungus, is seen on a rose-leaf on Plate V. Fig. 1. -On Fig. 10, however, of the same Plate, the Phragmídium may be seen -proceeding from Urédo, thus proving them to be but two states of the -same plant. There is room for any amount of observation and work in -connection with the life-histories of many of these fungi. - -Another species of Puccinia, found on the thistle, is shown on Plate -V. Fig. 7. Fig. 34 is the mould found upon decaying grapes, and called -therefrom, or from the clustered spores, Botrýtis. Some of the detached -spores are seen by its side. Fig. 35 is another species of the same -genus, termed Botrýtis parasítica, and is the cause of the well-known -“potato-disease.” - -The mosses and ferns afford an endless variety of interesting objects -to the microscopist; but as their numbers are so vast, and the details -of their structure so elaborate, they can only be casually noticed in -the present work. Fig. 38 represents a spore-case of the Polypodium, -one of the ferns, as it appears while in the act of bursting and -scattering the contents around. One of the spores is seen more -magnified below. The spore-cases of many ferns may be seen bursting -under the microscope, and have a very curious appearance, writhing and -twisting like worms, and then suddenly filling the field with a cloud -of spores. Fig. 9, Plate V., is a piece of the brown, chaff-like, scaly -structure found at the base of the stalk of male fern cells, showing -the manner in which a flat membrane is formed. Fig. 39 is a capsule of -the Hypnum, one of the mosses, showing the beautiful double fringe with -which its edge is crowned. Fig. 2, Plate V., is the capsule of another -moss, Polytríchum, to show the toothed rim; on the right hand is one of -the teeth much more magnified. - -Fig. 3, Plate V., is the capsule of the Jungermannia, one of the -liverworts, showing the “elaters” bursting out on every side, and -scattering the spores. Fig. 4 is a single elater much magnified, -showing it to be a spirally coiled filament, that, by sudden expansion, -shoots out the spores just as a child’s toy-gun discharges the arrow. -Fig. 5 is a part of the leaf of the Sphagnum moss, common in fresh -water, showing the curious spiral arrangement of secondary fibre which -is found in the cells, as well as the circular pores which are found -in each cell at a certain stage of growth. Just below, and to the -left hand, is a single cell greatly magnified, in order to show these -peculiarities more strongly. Fig. 8 is part of a leaf of Jungermannia, -showing the dotted cells. - -Fig. 6, Plate V., is a part of a rootlet of moss, showing how it is -formed of cells elongated and joined end to end. - -On the common mare’s-tail, or Equisétum, may be seen a very remarkable -arrangement for scattering the spores. On the last joint of the stem -is a process called a fruit-spike, being a pointed head around which -are set a number of little bodies just like garden-tables, with their -tops outward. One of these bodies is seen in Fig. 40. From the top of -the table depend a number of tiny pouches, which are called sporangia; -these lie closely against each other, and contain the spores. At the -proper moment these pouches burst from the inside, and fling out the -spores, which then look like round balls with irregular surfaces, as -shown in Fig. 40, _c_. This irregularity is caused by four elastic -filaments, knobbed at the end, which are originally coiled tightly -round the body of the spore, but by rapidly untwisting themselves cause -the spore to leap about, and so aid in the distribution. A spore with -uncoiled filaments is seen at Fig. 40, _b_. By breathing on them they -may be made to repeat this process at will. - -Fig. 36 is a common little sea-weed, called Ectocarpus siliculósus, -that is found parasitically adhering to large plants, and is figured in -order to show the manner in which the extremities of the branches are -developed into sporangia. Fig. 37 is a piece of the common green laver, -Ulva latíssima, showing the green masses that are ultimately converted -into zoospores, and by their extraordinary fertility cause the plant to -grow with such rapid luxuriance wherever the conditions are favourable. -Every possessor of a marine aquarium knows how rapidly the glass sides -become covered with growing masses of this plant. The smaller figure -above is a section of the same plant, showing that it is composed of a -double plate of cellular tissue. - -Fig. 41 is a piece of purple laver or “sloke,” Porphýra laciniáta, to -show the manner in which the cells are arranged in groups of four, -technically named “tetraspores.” This plant has only one layer of cells. - -On Plate V. may be seen a number of curious details of the higher algæ. - -Fig. 11 is the Sphacelária, so called from the curious capsule cells -found at the end of the branches, and termed sphacelæ. This portion -of the plant is shown more magnified in Fig. 12. Another sea-weed is -represented in Fig. 13, in order to show the manner in which the fruit -is arranged; and a portion of the same plant is given on a larger scale -at Fig. 14. - -A very pretty little sea-weed called Cerámium is shown at Fig. 15; and -a portion showing the fruit much more magnified is drawn at Fig. 22. -Fig. 23 is a little alga called Myrionéma, growing parasitically on the -preceding plant. - -Fig. 16 is a section of a capsule belonging to the Hálydris siliquósa, -showing the manner in which the fruit is arranged; and Fig. 17 shows -one of the spores more magnified. - -Fig. 18 shows the Polysiphónia parasítica, a rather common species of -a very extensive genus of sea-weeds, containing nearly three hundred -species. Fig. 19 is a portion of the stem of the same plant, cut across -in order to show the curious mode in which it is built up of a number -of longitudinal cells, surrounding a central cell of large dimensions, -so that a section of this plant has the aspect of a rosette when placed -under the microscope. A capsule or “ceramídium” of the same plant is -shown at Fig. 20, for the purpose of exhibiting the pear-shaped spores, -and the mode of their escape from the parent-cell previous to their -own development into fresh plants. The same plant has another form -of reproduction, shown in Fig. 21, where the “tetraspores” are seen -imbedded in the substance of the branches. There is yet a third mode -of reproduction by means of “antheridia,” or elongated white tufts at -the extremities of the branches. The cells produced by these tufts -fertilise the rudimentary capsules, and so fulfil the function of the -pollen in flowering plants. - -Fig. 25 is the Cladóphora, a green alga, figured to illustrate its mode -of growth; and Fig. 26 represents one of the red sea-weeds, Ptilóta -élegans, beautifully feathered, and with a small portion shown also -on a larger scale, in order to show its structure more fully. A good -contrast to this species is seen on Fig. 27, and the mode in which the -long, slender, filamentary fronds are built up of many-sided cells is -seen just to the left hand of the upper frond. Fig. 24 is a portion of -the lovely Delesséria sanguínea, given in order to show the formation -of the cells, as also the arrangement by which the indistinct nervures -are formed. - - -V. - - FIG. - 1. Rose Leaf, with fungus - 2. Moss capsule, Polytrichum - 3. Jungermannia, capsule - 4. Do. an elater more magnified - 5. Leaf of Moss, Sphagnum - 6. Rootlet, Moss - 7. Puccinia, from Thistle - 8. Jungermannia, leaf - 9. Scale from stalk of male fern - 10. Uredo - 11. Sphacelaria filicina - 12. Do. top, more magnified - 13. Seaweed, showing fruit - 14. Do. fruit, more magnified - 15. Ceramium - 16. Capsule, Halidrys - 17. Spore of do. - 18. Polysiphonia parasitica - 19. Do. stem, more magnified - 20. Do. Capsule, tetraspores escaping - 21. Do. fruit, another form - 22. Ceramium, fruit - 23. Myrionema, parasitic Seaweed - 24. Delesseria sanguinea, Frond - 25. Cladophora - 26. Ptilota elegans - 27. Enteromorpha clathrata - 28. Nitophyllum laceratum - -[Illustration: V.] - -The figure on the bottom left-hand corner of Plate V. is a portion of -the pretty Nitophyllum lacerátum, a plant belonging to the same family -as the preceding one. The specimen here represented has a gathering -of spores upon the frond, in which state the frond is said to be “in -fruit.” - -Fig. 27 represents a portion of the common sea-grass (_Enteromorpha_), -so common on rocks and stones between the range of high and low water. -On the left hand of the figure, and near the top, is a small piece of -the same plant much more magnified, in order to show the form of its -cells. - - - - -CHAPTER VII - - Antennæ, their Structure and Use--Eyes, Compound and - Simple--Breathing Organs--Jaws and their Appendages--Legs, Feet, - and Suckers--Digestive Organs--Wings, Scales, and Hairs--Eggs - of Insects--Hair, Wool, Linen, Silk, and Cotton--Scales of - Fish--Feathers--Skin and its Structure--Epithelium--Nails, Bone, and - Teeth--Blood Corpuscles and Circulation--Elastic Tissues--Muscle and - Nerve. - - -We now take leave of the vegetables for a time, and turn our attention -to the animal kingdom. - -On Plate VI. may be seen many beautiful examples of animal structures, -most of them being taken from the insect tribes. We will begin with the -antennæ, or horns, as they are popularly termed, of the insect. - -The forms of these organs are as varied as those of the insects to -which they belong, and they are so well defined that a single antenna -will, in almost every instance, enable a good entomologist to designate -the genus to which the insect belonged. The functions of the antennæ -are not satisfactorily ascertained. They are certainly often used as -organs of speech, as may be seen when two ants meet each other, cross -their antennæ, and then start off simultaneously to some task which is -too much for a single ant. This pretty scene may be witnessed on any -fine day in a wood, and a very animated series of conversations may -readily be elicited by laying a stick across their paths, or putting a -dead mouse or large insect in their way. - -I once saw a very curious scene of this kind take place at an ant’s -nest near Hastings. A great daddy long-legs had, unfortunately for -itself, settled on the nest, and was immediately “pinned” by an ant or -two at each leg, so effectually that all its struggles availed nothing. -Help was, however, needed, and away ran four or five ants in different -directions, intercepting every comrade they met, and by a touch of the -antennæ sending them off in the proper direction. A large number of the -wise insects soon crowded round the poor victim, whose fate was rapidly -sealed. Every ant took its proper place, just like a gang of labourers -under the orders of their foreman; and by dint of pushing and pulling, -the long-legged insect was dragged to one of the entrances of the nest, -and speedily disappeared. - -Many of the ichneumon-flies may also be seen quivering their antennæ -with eager zeal, and evidently using them as feelers, to ascertain the -presence of the insect in which they intend to lay their eggs; and many -other similar instances will be familiar to anyone who has been in the -habit of watching insects and their ways. - -It is, however, most likely that the antennæ serve other purposes than -that which has just been mentioned, and many entomologists are of -opinion that they serve as organs of hearing. - -Fig. 15, Plate VI., represents a part of one of the joints belonging to -the antennæ of the common house-fly; it is seen to be covered with a -multitude of little depressions, some being small, and others very much -larger. A section of the same antenna, but on a larger scale, is shown -by Fig. 16, in order to exhibit the real form of these depressions. -Nerves have been traced to these curious cavities, which evidently -serve some very useful purpose, some authors thinking them to belong to -the sense of smell, and others to that of hearing. Perhaps they may be -the avenues of some sensation not possessed by the human race, and of -which we are therefore ignorant. Fig. 17 represents a section of the -antennæ of an ichneumon-fly, to show the structure of these organs of -sense. - -We will now glance cursorily at the forms of antennæ which are depicted -in the Plate. - -Fig. 1 is the antenna of the common cricket, which consists of a vast -number of little joints, each a trifle smaller than the preceding one, -the whole forming a long, thread-like organ. Fig. 2 is taken from the -grasshopper, and shows that the joints are larger in the middle than at -either end. - -Figs. 3 and 5 are from two minute species of cocktailed beetles -(_Staphylínidæ_), which swarm throughout the summer months, and even in -the winter may be found in profusion under stones and moss. The insect -from which Fig. 5 was taken is so small that it is almost invisible -to the naked eye, and was captured on the wing by waving a sheet of -gummed paper under the shade of a tree. These are the tiresome little -insects that so often get into the eye in the summer, and cause such -pain and inconvenience until they are removed. - -Fig. 4 shows the antenna of the tortoise beetle (_Cássida_), so common -on many leaves, and remarkable for its likeness to the reptile from -which it derives its popular name. Fig. 3 is from one of the weevils, -and shows the extremely long basal joint of the antennæ of these -beetles, as well as the clubbed extremity. Fig. 7 is the beautifully -notched antenna of the cardinal beetle (_Pyrochróa_), and Fig. 11 is -the fan-like one of the common cockchafer. This specimen is taken from -a male insect, and the reader will find his trouble repaid on mounting -one of these antennæ as a permanent object. - -Fig. 12 is an antenna from one of the common ground beetles (_Cárabus_) -looking like a string of elongated pears, from the form of the joints. -The reader will see that in beetles he is sure to find eleven joints in -the antennæ. - -Fig. 10 is the entire antenna of a fly (_Syrphus_), one of those pretty -flies which may be seen hovering over one spot for a minute, and then -darting off like lightning to hang over another. The large joint is the -one on which are found those curious depressions that have already been -mentioned. Fig. 8 is one of the antennæ of a tortoise-shell butterfly -(_Vanessa_), showing the slender, knobbed form which butterfly -antennæ assume; and Figs. 13 and 14 are specimens of moths’ antennæ, -showing how they always terminate in a point. Fig. 13 is the beautiful -feathery antenna of the ermine moth (_Spilosóma_); and Fig. 14 is the -toothed one of the tiger moth (_Arctia caja_). In all these feathered -and toothed antennæ of moths, the male insects have them much more -developed than the female, probably for the purpose of enabling them -to detect the presence of their mates, a property which some possess -in wonderful perfection. The male oak-egger moth, for example, can be -obtained in any number by putting a female into a box with a perforated -lid, placing the box in a room, and opening the window. In the course -of the evening seven or eight males are seen to make their appearance, -and they are so anxious to get at their intended mate that they will -suffer themselves to be taken by hand. - -Fig. 9 is an antenna of the male gnat, a most beautiful object, -remarkable for the delicate transparency of the joints, and the -exquisitely fine feathering with which they are adorned. - -We now arrive at the eyes of the insects, all of which are very -beautiful, and many singularly full of interest. - -In the centre of Plate VI. may be seen the front view of the head -of a bee, showing both kinds of eyes, three simple eyes arranged -triangularly in the centre, and two large masses, compound eyes, at the -sides. - -The simple eyes, termed “ocelli,” are from one to three in number, and -usually arranged in a triangular form between the two compound eyes. -Externally they look merely like shining rounded projections, and can -be seen to great advantage in the dragon-flies. The compound eyes may -be considered as aggregations of simple eyes, set closely together, -and each assuming a more or less perfect six-sided form. Their number -varies very greatly; in some insects, such as the common fly, there are -about four thousand of these simple eyes in one compound one, in the -ant only fifty, in the dragon-fly about twelve thousand, and in one of -the beetles more than twenty-five thousand. - -Fig. 18 shows a portion of the compound eye of the Atalanta butterfly, -and Fig. 20 the same organ of the death’s-head moth. A number of -the protecting hairs may be seen still adhering to the eye of the -butterfly. Fig. 22 is a remarkably good specimen of the eye of a fly -(_Helióphilus_), showing the facets, nearly square, the tubes to -which they are attached, and portions of the optic nerves. Fig. 23 -is part of the compound eye of a lobster, showing the facets quite -square. All these drawings were taken by the camera lucida from my own -preparations, so that I can answer for their authenticity. - -On Plate VIII. Figs. 6 and 12, the reader will find two more examples -of eyes, these being taken from the spiders. Fig. 6 is an example of -the eight eyes of the well-known zebra spider, so common on our garden -walls and similar situations, hunting incessantly after flies and other -prey, and capturing them by a sudden pounce. The eyes are like the -ocelli of insects, and are simple in their construction. The number, -arrangement, and situation of the eyes is extremely varied in spiders, -and serves as one of the readiest modes of distinguishing the species. -Fig. 12, Plate VIII., represents one of the curious eyes of the common -harvest spider, perched on a prominence or “watch-tower” (as it has -been aptly named), for the purpose of enabling the creature to take a -more comprehensive view of surrounding objects. - - * * * * * - -Returning to Plate VI., in Fig. 21 we see a curiously branched -appearance, something like the hollow root of a tree, and covered with -delicate spiral markings. This is part of the breathing apparatus of -the silkworm, extracted and prepared by myself for the purpose of -showing the manner in which the tubes branch off from the “spiracle” -or external breathing-hole, a row of which may be seen along the -sides of insects, together with the beautiful spiral filament which -is wound round each tube for the purpose of strengthening it. One of -these spiracles may be seen in the neck of the gnat (Fig. 27). Another -spiracle, more enlarged, may be seen on Plate VII. Fig. 34, taken from -the wireworm, _i.e._ the larva of the skipjack beetle (_Eláter_), to -show the apparatus for excluding dust and admitting air. The object of -the spiral coil is very evident, for as these breathing-tubes extend -throughout the whole body and limbs, they would fail to perform their -office when the limbs were bent, unless for some especial provision. -This is achieved by the winding of a very strong but slender filament -between the membranes of which the tube is composed, so that it always -remains open for the passage of air throughout all the bends to which -it may be subjected. Flexible tubes for gas and similar purposes are -made after the same fashion, spiral metal wire being coiled within -the india-rubber pipe. A little piece of this thread is seen unwound -at the end of a small branch towards the top, and this thread is so -strong that it retains its elasticity when pulled away from the tube, -and springs back into its spiral form. I have succeeded in unwinding -a considerable length of this filament from the breathing-tube of a -humble bee. - -Fig. 28 represents the two curious tubercles upon the hinder quarters -of the common green-blight, or Aphis, so very common on our garden -plants, as well as on many trees and other vegetables. From the tips of -these tubercles exudes a sweet colourless fluid, which, after it has -fallen upon the leaves, is popularly known by the name of honey-dew. -Ants are very fond of this substance, and are in the habit of haunting -the trees upon which the aphides live, for the purpose of sucking the -honey-dew as it exudes from their bodies. A drop of this liquid may be -seen on the extremity of the lower tubercle. - -The head of the same insect may be seen in Fig. 24, where the reader -may observe the bright scarlet eye, and the long beak with which the -aphis punctures the leaves and sucks the sap. Fig. 29 is the head of -the sheep-tick, exhibiting the organ by which it pierces the skin of -the creature on which it lives. Fig. 25 is the head of another curious -parasite found upon the tortoise, and remarkable for the powerful -hooked apparatus which projects in front of the head. - -Turning to Plate VII. Fig. 4, we find the head of a ground beetle -(_Cárabus_), valuable as exhibiting the whole of the organs of the head -and mouth. - -Immediately above the compound eyes are seen the roots of the antennæ, -those organs themselves being cut away. Above there are two pairs of -similarly constructed organs termed the “maxillary palpi,” because -they belong to the lesser jaws or maxillæ, seen just within the pair -of great curved jaws called the mandibles, which are extended in so -threatening a manner. The “labial palpi,” so called because they -belong to the “labium,” or under lip, are seen just within the others; -the tongue is seen between the maxillæ, and the chin or “mentum” -forms a defence for the base of the maxillæ and the palpi. A careful -examination of a beetle’s mouth with the aid of a pocket lens is very -instructive as well as interesting. - -Fig. 1 on the same Plate shows the jaws of the hive bee, where the same -organs are seen modified into many curious shapes. In the centre may be -seen the tongue, elongated into a flexible and hair-covered instrument, -used for licking the honey from the interior of flowers. At each side -of the tongue are the labial palpi, having their outermost joints very -small, and the others extremely large, the latter acting as a kind -of sheath for the tongue. Outside the labial palpi are the maxillæ, -separated in the specimen, but capable of being laid closely upon each -other, and outside all are the mandibles. - - -VI. - - FIG. - 1. Antenna, Cricket - 2. Do. Grasshopper - 3. Do. Staphylinus - 4. Do. Cassida - 5. Do. Staphylinus - 6. Do. Weevil - 7. Do. Pyrochroa - 8. Do. Butterfly, Tortoiseshell - 9. Do. Gnat, male - 10. Do. Syrphus - 11. Do. Cockchafer, male - 12. Do. Ground Beetle - 13. Do. Ermine Moth - 14. Do. Tiger Moth - 15. Do. Blowfly - 16. Do. do. section - 17. Do. Ichneumon - 18. Eye of Butterfly, Atalanta - 19. Eyes, Bee - 20. Eye, Death’s Head Moth - 21. Breathing-tube, Silkworm - 22. Eye, Heliophilus - 23. Do. Lobster - 24. Do. Aphis of Geranium - 25. Head, Parasite of Tortoise - 26. Hind leg, Aphis of Geranium - 27. Head, Gnat - 28. “Paps” of Aphis - 29. Head, Sheep-tick - 30. Foot, Tipula - -[Illustration: VI.] - -The curiously elongated head of the scorpion-fly (_Panorpa_), seen -at Fig. 7, affords another example of the remarkable manner in which -these organs are developed in different insects. Another elongated -head, belonging to the daddy long-legs, is seen in Plate VI. Fig. 27, -and well shows the compound eyes, the antennæ, and the palpi. Fig. 2 -represents the coiled tongue of the Atalanta butterfly; it is composed -of the maxillæ, very greatly developed, and appearing as if each -had originally been flat, and then rolled up so as to make about -three-fourths of a tube. A number of projections are seen towards the -tip, and one of these little bodies is shown on a larger scale at -Fig. 3. These curious organs have probably some connection with the -sense of taste. Along the edges of the semi-tubes are arranged a number -of very tiny hooks, by means of which the insect can unite the edges at -will. - -Fig. 11, in the centre of the Plate, shows one of the most curious -examples of insect structure, the proboscis or trunk of the common -bluebottle-fly. The maxillary palpi covered with bristles are seen -projecting at each side, and upon the centre are three lancet-like -appendages, two small and one large, which are used for perforating -various substances on which the insect feeds. The great double disc -at the end is composed of the lower lip greatly developed, and is -filled with a most complex arrangement of sucking-tubes, in order to -enable it to fulfil its proper functions. The numerous tubes which -radiate towards the circumference are strengthened by a vast number -of partial rings of strong filamentary substance, like that which we -have already seen in the breathing-tube of the silkworm. Some of these -partial rings are seen on Fig. 12, a little above. The mode in which -the horny matter composing the rings is arranged upon the tubes is most -wonderful, and requires a tolerably high power to show it. The fine -hairs upon the proboscis itself afford most admirable practice for the -young microscopist. They should, when properly lighted and focused, be -quite black and sharp. Any errors of manipulation will cause them to be -“fuzzy.” - -Fig. 5 shows the tongue of the common cricket, a most elegantly formed -organ, having a number of radiating bands covered with zigzag lines, -due to the triangular plates of strengthening substance with which they -are furnished, instead of the rings. A portion more highly magnified -is shown at Fig. 6, exhibiting the manner in which the branches are -arranged. - - * * * * * - -The legs of insects now claim our attention. - -Fig. 9, Plate VII., shows the “pro-leg” of a caterpillar. The pro-legs -are situated on the hinder parts of the caterpillar, and, being set in -pairs, take a wonderfully firm hold of a branch or twig by pressure -toward each other. Around the pro-legs are arranged a series of sharp -hooks, set with their points inwards, for greater power in holding. -Fig. 10 represents one of the hooks more magnified. - -Fig. 15 is the lower portion of the many-jointed legs of the -long-legged spider (_Phalángium_), the whole structure looking very -like the antenna of the cricket. Fig. 17 is the leg of the glow-worm, -showing the single claw with which it is armed. Fig. 26 shows the foot -of the flea, furnished with two simple claws. Fig. 16 is the foot of -the Trombídium, a genus of parasitic creatures, to which the well-known -harvest-bug belongs. Fig. 26, Plate VI., shows the leg of the green -Aphis of the geranium, exhibiting the double claw, and the pad or -cushion, which probably serves the same purpose as the pads found upon -the feet of many other insects. Fig. 8 is the lower portion of the leg -of the ant, showing the two claws and the curious pad in the centre, -by means of which the insect is able to walk upon slippery surfaces. -The Típula has a foot also furnished with a single pad (see Plate VI. -Fig. 30). This organ is seen under a very high power to be covered with -long hair-like appendages, each having a little disc at the end, and -probably secreting some glutinous fluid which will enable the creature -to hold on to perpendicular and smooth surfaces. Many of my readers -will doubtless have noticed the common fly, towards the end of autumn, -walking stiffly upon the walls, and evidently detaching each foot with -great difficulty, age and infirmity having made the insect unable to -lift its feet with the requisite force. - -Fig. 21 is the foot of one of the ichneumon-flies (_Ophíon_), the -hairy fringe being apparently for the purpose of enabling it to hold -firmly to the caterpillar in which it is depositing its eggs, and -which wriggles so violently under the infliction that it would soon -throw its tormentor had not some special means been provided for the -purpose of enabling the latter to keep its hold. Fig. 20 is a beautiful -example of a padded foot, taken from the little red parasitic creature -so plentifully found upon the dor or dung beetle (_Geotrúpes_), and of -which the afflicted insect is said to rid itself by lying on its back -near an ant’s nest, and waiting until the ants carry off its tormentors. - -Fig. 18 is the foot of the common yellow dung-fly (plentiful in pasture -lands), having two claws and two pads; and Fig. 19 shows the three pads -and two claws found in the foot of the hornet-fly (_Ásilus_). - -Few microscopic objects call forth such general and deserved admiration -as the fore-foot of the male water-beetle (_Dytiscus_), when properly -prepared and mounted, for which see Fig. 13. - -On examining this preparation under the microscope, it is seen that -three of the joints are greatly expanded, and that the whole of their -under surface is covered profusely with certain wonderful projections, -which are known to act as suckers. One of them is exceedingly large, -and occupies a very considerable space, its hairs radiating like the -rays of the heraldic sun. Another is also large, but scarcely half -the diameter of the former, and the remainder are small, and mounted -on the extremities of delicate foot-stalks, looking something like -wide-mouthed trumpets. In the specimen from which the drawing was taken -the smaller suckers are well shown, as they protrude from the margin of -the foot. - -One of the larger suckers is seen more magnified on Fig. 14. - -Plate VIII. Fig. 1, exemplifies the manner in which the muscles of -insects do their work, being well attached in the limbs to the central -tendon, and pulling “with a will” in one direction, thus giving very -great strength. This leg is taken from the water boatman (_Notonecta_), -and has been mounted in Canada balsam. - -On Plate VII. Fig. 29, may be seen a curiously formed creature. This -is the larva of the tortoise beetle (_Cássida_), the skin having been -flattened and mounted in Canada balsam. The spiracles are visible -along the sides, and at the end is seen a dark fork-like structure. -This is one of the peculiarities of this creature, and is employed for -the purpose of carrying the refuse of its food, which is always piled -upon its back, and retained in its place by the forked spines, aided -probably by the numerous smaller spines that project from the side. - -Fig. 33 shows part of the stomach and gastric teeth of the grasshopper. -This structure may be seen to perfection in the “gizzard,” as it is -called, of the great green locust of England (_Ácrida viridíssima_). -The organ looks like a sudden swelling of the œsophagus, and when slit -longitudinally under water, the teeth may be seen in rows set side by -side, and evidently having a great grinding power. The common house -cricket has a similar organ of remarkable beauty. Just above (Fig. 27) -is the corresponding structure in the hive bee, three of the teeth -being shown separately at Fig. 28. - - * * * * * - -We now cast a rapid glance at the wings of insects. - -They have no analogy, except in their use, with the wings of birds, as -they are not modifications of existing limbs, but entirely separate -organs. They consist of two membranes united at their edges, and -traversed and supported by sundry hollow branches or “nervures,” which -admit air, and serve as useful guides to entomologists for separating -the insects into their genera. Indeed, the general character of the -wings has long been employed as the means of dividing the insect race -into their different orders, as may be seen in any work on entomology. -The typical number of wings is four, but it often happens that two are -almost wholly absent, or that the uppermost pair are thickened into a -shelly kind of substance which renders them useless for flight; while -in many insects, such as the ground beetles and others, the upper wings -become hardened into firm coverings for the body, and the lower pair -are shrivelled and useless. - -Fig. 22 shows two of the wings of a humble bee, together with their -nervures, and the peculiar system by which the upper and lower pair are -united together at the will of the insect. At the upper edge of the -lower wing, and nearly at its extremity, may be seen a row of very tiny -hooks, shown on a larger scale at Fig. 25. These hooklets hitch into -the strengthened membrane of the upper wing, which is seen immediately -above them, and so conjoin the two together. The curious wing-hooks of -the Aphis may be seen on Fig. 24, very highly magnified. - -Fig. 31 is the wing of the midge (_Psychóda_), that odd little insect -which is seen hopping and popping about on the windows of outhouses -and similar localities, and is so hard to catch. The whole wing is -plentifully covered with elongated scales, and is a most lovely object -under any power of the microscope. These scales run along the nervures -and edges of the wings, and part of a nervure is shown more highly -magnified at Fig. 32. - -At Fig. 23 is shown the wing of one of the hemipterous insects, common -along the banks of ditches and in shady lanes, and known by the name -of Cíxius. It is remarkable for the numerous spots which stud the -nervures, one being always found at each forking, and the others being -very irregularly disposed. - -Fig. 30 is one of the balancers or “haltéres” of the house-fly. These -organs are found in all the two-winged insects, and are evidently -modifications of the second pair of wings. They are covered with -little vesicles, and protected at their base by scales. Some writers -suppose that the sense of smell resides in these organs. Whatever other -purpose they may serve, they clearly aid in the flight, as, if the -insect be deprived of one or both of the balancers, it has the greatest -difficulty in steering itself through the air. - -The wings of insects are mostly covered with hairs or scales, several -examples of which are given in Plate VIII. Fig. 4 shows one of the -scales of the Adippe or fritillary butterfly, exhibiting the double -membrane--part of which has been torn away--and the beautiful lines of -dots with which it is marked. The structure of the scales is further -shown by a torn specimen of tiger moth scale seen on Fig. 16. On -many scales these dots assume a “watered” aspect when the focus or -illumination changes, an example of which may be seen in Fig. 15, a -scale of the peacock butterfly. - -Fig. 11 is one of the ordinary scales of the azure blue butterfly, -and Fig. 10 shows one of the curious “battledore” scales of the same -insect, with its rows of distinct dottings. Fig. 14 is one of the -prettily tufted scales of the orange-tip butterfly, and Fig. 8 is the -splendid branched scale of the death’s-head moth. Fig. 19 shows a scale -of the sugar-runner (_Lepisma saccharína_), a little silvery creature -with glistening skin, and long bristles at the head and tail, that is -found running about cupboards, window-sills, and similar places. It -is not easy to catch with the fingers, as it slips through them like -oil; but by holding a cover-glass in a pair of forceps, and pressing it -upon one of the little creatures, a number of the scales may be caused -to adhere to it, and these should be mounted dry for examination. The -gnats also possess very pretty scales, with the ribs projecting beyond -the membrane. - - -VII. - - FIG. - 1. Tongue, Hive Bee - 2. Do. Tortoiseshell Butterfly - 3. Do. do. one of the barrel-shaped bodies - 4. Head, Violet Ground Beetle (Carabus) - 5. Tongue, Cricket - 6. Do. do. - 7. Head, Scorpion Fly (Panorpa) - 8. Leg, Ant - 9. Proleg, Caterpillar - 10. Do. do. single hook - 11. Proboscis, Fly - 12. Do. do. “modified trachea” - 13. Part of Foreleg of Water Beetle (Acilius) - 14. Do. large sucker - 15. Leg, long-legged Spider (Phalangium) - 16. Do. Harvest-bug (Trombidium) - 17. Do. Glow-worm - 18. Do. Dung fly - 19. Do. Asilus - 20. Do. Acarus of Dor-beetle - 21. Claws and Pad, Ophion - 22. Wings, Humble Bee - 23. Do. - 24. Wing hooks, hind wing of Aphis - 25. Wing hooks, Humble Bee - 26. Foot, Flea - 27. Stomach and gastric teeth, Bee - 28. Three teeth of do. - 29. Cast skin, Larva of Tortoise Beetle (Cassida) - 30. Balancer, Blow fly - 31. Wing, Midge (Psychoda) - 32. Do. do. part of a nervure with scales - 33. Stomach and gastric teeth, Grasshopper - 34. Spiracle, Wire-worm - -[Illustration: VII.] - -Fig. 21 is a scale from the common spring-tail (_Podúra plúmbea_), a -little creature which is found plentifully in cellars and other damp -places, skipping about with great activity. Some flour scattered on a -piece of paper is a sure trap for these little beings. Fig. 3 is one -of the scales taken from the back of the celebrated diamond beetle, -showing the cause of the magnificent gem-like aspect of that insect. We -have in England many beetles of the same family--the weevils--which, -although much smaller, are quite as splendid when exhibited under a -microscope by reflected light. The wing-case or “elytron” of a little -green weevil, very common in the hedges, may be seen on Plate XII. -Fig. 10. - -The reader will observe that all these scales are furnished with little -root-like appendages, by means of which they are affixed to the insect. -Fig. 13 shows a portion of the wing of the azure blue butterfly, from -which nearly all the scales have been removed, for the purpose of -exhibiting the pits or depressions in which they had formerly been -fastened, and one or two of the scales are left still adherent to their -places. The scales are arranged in equal rows like the slates of a -housetop, as may be seen on Fig. 18, which represents part of the same -wing, to show the scales overlapping each other, and the elegant form -which they take near the edges of the wing, so as to form a delicate -fringe. The long hair-like down which covers the legs and bodies of the -moths and butterflies (which are called Lepidóptera, or scale-winged -insects, in consequence of this peculiarity), is seen under the -microscope to be composed of scales very much elongated, as is shown in -Fig. 17, a portion taken from the leg of a tiger moth. - - * * * * * - -The eggs of insects are all very beautiful, and three of the most -curious forms are given on Plate VIII. - -Fig. 2 is the empty egg of the gad-fly, as it appears when fastened to -a hair of the horse. Fig. 5 represents the pretty ribbed egg of the -common tortoise-shell butterfly; and Fig. 7 is the very beautiful egg -of the very horrid bed-bug, worthy of notice on account of the curious -lid with which its extremity is closed, by means of which the young -larva creeps out as soon as it is hatched. - -The feathers of birds, and the fur of animals, will furnish many -examples of the eggs of parasites, some of which are of extreme beauty. -The feather or hair may be mounted in a cell without disturbing the -eggs, which should, however, be heated sufficiently to kill the embryo -if present. - -Fig. 9 shows the penetrating portions of the sting of the wasp. The -two barbed stings, which seem to be the minute prototypes of the -many-barbed spears of the South Sea islanders, are seen lying one at -each side of their sheath, and a single barb is drawn a little to the -left on a very much larger scale. It is by reason of these barbs that -the sting is always left adhering to the wound, and is generally drawn -wholly out of the insect, causing its death in a short while. - -The sting is only found in female insects, and is supposed to be -analogous to the “ovipositor” of other insects, _i.e._ the instrument -by which the eggs are deposited in their places. Fig. 20 shows the -curious egg-placing apparatus of one of the saw-flies. The backs of -these “saws” work in grooves, and they work alternately, so that the -fly takes but a very short time in cutting a slit in the young bark -of a tender shoot, and laying her eggs in the slit. When she has -completed one of these channels, she sets to work upon another, and in -the early spring the young branches of the gooseberry bushes may be -seen plentifully covered with these grooves and the eggs. When hatched, -black caterpillar-like grubs from the eggs issue, and devastate the -bushes sadly, turning in process of time into blackish flies, which are -seen hovering in numbers over the gooseberries, and may be killed by -thousands. - - * * * * * - -The scales and hairs of other animals deserve great attention. Fig. 23 -is a single hair of the human beard, as it often appears when tied in -a knot--by Queen Mab and her fairies, according to Mercutio. Fig. 22 -is a portion of the same hair as it appears when splitting at its -extremity. The structure of the hair is not, however, so well seen in -this object as in that represented on Fig. 24, which is a beautiful -example of white human hair that once adorned the head of the victor -of Waterloo. It formed one of a tiny lock given to me by a friend, and -is so admirable an example of human hair, that I forthwith mounted -it for the microscope. In this hair the cells may be seen extending -down its centre, and the peculiar roughened surface produced by the -flattened cells which are arranged around its circumference are also -seen. By steeping in caustic potash, these scales can be separated, -but generally they lie along the hair in such a manner that if the -hair be drawn through the fingers from base to point, their projecting -ends permit it to pass freely; whilst if it be drawn in the reverse -direction, they cause it to feel very harsh to the touch. - -In the sheep’s wool (Fig. 30) this structure is much more developed, -and gives to the fibres the “felting” power that causes them to -interlace so firmly with each other, and enables cloth--when really -made of wool--to be cut without unravelling. Fig. 37 is the smooth hair -of the badger; and Fig. 34 is the curious hair of the red deer, which -looks as if it had been covered with a delicate net. - -Fig. 28 is the soft, grey, wool-like hair of the rat; and Fig. 29 -is one of the larger hairs that protrude so plentifully, and form -the glistening brown coat of that animal. Fig. 38 is the curiously -knobbed hair of the long-eared bat, the knobs being formed of -protuberant scales that can easily be scraped off. Fig. 31 shows a -hair of the common mole; and Fig. 32 is one of the long hairs of the -rabbit. Fig. 27 is a flat hair of the dormouse, slightly twisted, the -difference in the breadth showing where the twist has taken place. The -hair of the mouse is beautifully ribbed, so as to look like a ladder. -Fig. 26 is one of the very long hairs that so thickly clothe the tiger -moth caterpillar; and Fig. 25 is a beautifully branched hair taken from -the common humble bee. - -All hairs should be examined by polarised light, with a plate of -selenite, when most gorgeous colour effects may be obtained. - -The four fibres mostly used in the manufacture of apparel are: wool, -Fig. 30, which has already been described; linen, Fig. 39; cotton, -Fig. 40; and silk, Fig. 41. The structure of each is very well marked -and easily made out with the microscope; so that an adulterated article -can readily be detected by a practised eye. Cotton is the most common -adulteration of silk and linen fabrics, and may at once be detected -by its flat twisted fibre. Silk is always composed of two parallel -threads, each proceeding from one of the spinnerets of the caterpillar, -and it may be here remarked that if these threads are not quite -parallel the silk is of bad quality. Silken fibre is always covered, -when new, with a kind of varnish, usually of a bright orange colour, -which gives the undressed “floss” silk its peculiar hue, but which is -soluble and easily washed away in the course of manufacture. - -Figs. 35 and 36 are the small and large hairs of that magnificent -creature, the sea mouse (_Aphrodíte aculeáta_), whose covering, -although it lies in the mud, glows with every hue of the rainbow, and -in a brilliant light is almost painfully dazzling to the eye. - -VIII. - - FIG. - 1. Boat-fly, leg - 2. Gadfly, empty egg - 3. Diamond Beetle, scale - 4. Scale, Fritillary, Adippe - 5. Egg, Tortoiseshell Butterfly - 6. Head and Eyes, Zebra Spider - 7. Eyes, Bed-Bug - 8. Scale, Death’s-Head Moth - 9. Sting, Wasp - 10. Scale, battledore, Azure blue - 11. Do. ordinary scale - 12. Eye, Harvest Spider - 13. Wing Membrane, Azure Blue - 14. Scale, Anthocera cardaminis - 15. Do. Peacock Butterfly - 16. Do. Tiger Moth - 17. Do. Thigh of Tiger Moth - 18. Wing and Scales, Azure Blue - 19. Scale, Lepisma - 20. Saws, Sawfly - 21. Scale, Podura - 22. Hair, Black Human - 23. Do. Human Beard - 24. Do. do. aged - 25. Do. Humble Bee - 26. Do. Tiger Moth, Larva - 27. Do. Dormouse - 28. Do. Rat - 29. Do. do. long hair - 30. Do. Sheep - 31. Do. Mole - 32. Do. Rabbit - 33. Scale, Greenbone Pike - 34. Hair, Red Deer - 35. Do. fine, Sea Mouse - 36. Do. do. large - 37. Do. do. Badger - 38. Do. do. long-eared Bat - 39. Fibre, Linen - 40. Do. Cotton - 41. Do. Silk - 42. Scale, Perch - 43. Do. do. - -[Illustration: VIII.] - -The scales of some of the fishes are shown on Plate VIII., in order -to exhibit their mode of growth by successive layers. The scales are -always enveloped in membranous sacs, and in some cases, as in the -eel, they do not project beyond the surface, and require some little -observation to detect them. A scale of an eel is shown on Plate XI. -Fig. 14, and is a magnificent object under polarised light. Fig. 33 -is a scale of the greenbone pike; and Figs. 42 and 43 are scales of -the perch, showing the roots by which they are held in their places. -The roach, dace, bleak, and many other similar fish have a beautiful -silvery substance on the under surface of the scales, which was greatly -used in the manufacture of artificial pearls, glass beads being thinly -coated in the interior with the glittering substance, and then filled -in with wax. A piece of sole-skin, when preserved in Canada balsam and -placed under the microscope, is a very beautiful object. - -More examples of hairs, and other processes from the skin, together -with the structure of the skin itself, of bone, of blood, and the mode -in which it circulates, are given on Plate X. - -In all important points of their structure the feathers of birds -are similar to the hairs of animals, and are developed in a similar -manner. They are all composed of a quill portion, in which the pith -is contained, and of a shaft, which carries the vane, together with -its barbs. The form of each of these portions varies much, even in -different parts of the same bird, and the same feather has almost -always two kinds of barbs; one close and firm, and the other loose, -floating, and downy. If a small feather be plucked from the breast -or back of a sparrow or any other small bird, the upper part of the -feather is seen to be close and firm, while the lower is loose and -downy, the upper part being evidently intended to lie closely on the -body and keep out the wet, while the lower portion affords a soft and -warm protection to the skin. - -Fig. 12, Plate X., shows the feather of a peacock, wherein the barbs -are very slightly fringed and lie quite loosely side by side. Fig. 18 -is part of the same structure, in a duck’s feather, wherein are seen -the curious hooks which enable each vane to take a firm hold of its -neighbour, the whole feather being thus rendered firm, compact, and -capable of repelling water. The reader will not fail to notice the -remarkable analogy between these hooks and those which connect the -wings of the bee. - -Fig. 17 is a part of the shaft of a young feather taken from the -canary, given for the purpose of showing the form of the cells -of which the pith is composed. Fig. 20 is part of the down from a -sparrow’s feather, showing its peculiar structure; and Fig. 21 is a -portion of one of the long drooping feathers of the cock’s tail. - -Fig. 13 exhibits a transverse section of one of the large hairs or -spines from the hedgehog, and shows the disposition of the firm, -horn-like exterior, and the arrangement of the cells. Sections of -various kinds of hair are interesting objects, and are easily made by -tying a bundle of them together, soaking them in gum, hardening in -spirit, and then cutting thin slices with a razor. A little glycerine -will dissolve the gum, and the sections of hair will be well shown. -Unless some such precaution be taken, the elasticity of the hair will -cause the tiny sections to fly in all directions, and there will be no -hope of recovering them. - -Several examples of the skin are also given. Fig. 27 is a section -through the skin of the human finger, including the whole of one of the -little ridges which are seen upon the extremity of every finger, and -half of two others. The cuticle, epidermis, or scarf-skin, as it is -indifferently termed, is formed of cells or scales, much flattened and -horny in the upper layers, rounder and plumper below. The true skin, -or “cutis,” is fibrous in structure, and lies immediately beneath, the -two together constituting the skin, properly so called. Beneath lies a -layer of tissue filled with fatty globules, and containing the glands -by which the perspiration is secreted. - -One of the tubes or channels by which these glands are enabled to -pour their contents to the outside of the body, and, if they be kept -perfectly clean, to disperse them into the air, is seen running up -the centre of the figure, and terminating in a cup-shaped orifice on -the surface of the cuticle. On the palm of the hand very nearly three -thousand of these ducts lie within the compass of a square inch, and -more than a thousand in every square inch of the arm and other portions -of the body, so that the multitude of these valuable organs may be well -estimated, together with the absolute necessity for keeping the skin -perfectly clean in order to enjoy full health. - -Fig. 1 shows a specimen of epidermis taken from the skin of a frog, -exhibiting the flattened cells which constitute that structure, and -the oval or slightly elongated nuclei, of which each cell has one. In -Fig. 32, a portion of a bat’s wing, the arrangement of the pigment -is remarkably pretty. Immediately above, at Fig. 31, is some of the -pigment taken from the back of the human eye-ball. The shape of the -pigment cells is well shown. Similar specimens may easily be obtained -from the back of a sheep’s eye which has been hardened in spirit, or -from that of a boiled fish. Fig. 33 shows the pigment in the shell of -the prawn. - - * * * * * - -On various parts of animal structures, such as the lining of internal -cavities, the interior of the mouth, and other similar portions of -the body, the cells are developed into a special form, which is -called “Epithélium,” and which corresponds to the epidermis of the -exterior surface of the body. The cells which form this substance are -of different shapes, according to their locality. On the tongue, for -example (for which see Fig. 11), they are flattened, and exhibit their -nucleus, in which the nucléolus may be discovered with a little care. -Cells of this kind are rounded, as in the case just mentioned, or -angular, and in either case they are termed squamous (_i.e._, scaly) -epithelium. Sometimes they are like a number of cylinders, cones, or -pyramids, ranged closely together, and are then called cylindrical -epithelium. Sometimes the free ends of cylindrical epithelium are -furnished with a number of vibrating filaments or cilia, and in this -case the structure is called “ciliated” epithelium. Cylindrical -epithelium may be found in the ducts of the glands which open into -the intestines, as well as in the glands that secrete tears; and -ciliated epithelium is seen largely in the windpipe, the interior of -the nose, etc. A specimen taken from the nose is seen at Fig. 15. A -beautiful example of ciliated epithelium is to be found in the gills -of the mussel. A portion of one of the yellowish bands which lie along -the edge of the shell on the opening side is carefully removed with -sharp scissors, and examined in the shell-liquor, being protected -from pressure by placing a piece of paper beneath each end of the -cover-glass. Such a preparation is shown in Plate IX. Fig. 39, but no -drawing can give an idea of its wonderful beauty and interest. The -cilia will continue to move for a long time after removal from the -shell. - - * * * * * - -Bone in its various stages is figured on Plate X. - -Fig. 9 is a good example of human bone, and is a thin transverse -section taken from the thigh. When cut across, bone exhibits a whitish -structure filled with little dottings that become more numerous towards -the centre, and are almost invisible towards the circumference. In the -centre of the bone there is a cavity, which contains marrow in the -mammalia and air in the birds. When placed under a microscope, bone -presents the appearance shown in the illustration. - -The large aperture in the centre is one of innumerable tubes that run -along the bone, and serve to allow a passage to the vessels which -convey blood from one part of the bone to another. They are technically -called Haversian canals, and if a longitudinal section be made they -will be found running tolerably parallel, and communicating freely -with each other. Around each Haversian canal may be seen a number of -little black spots with lines radiating in all directions, and looking -something like flattened insects. These are termed bone-cells or -“lacúnæ,” and the little black lines are called “canalículi.” In the -living state they contain cells which are concerned in the growth of -the bone, and these may be made evident by softening fresh bone with -acid, cutting sections of it, and staining. When viewed by transmitted -light the lacunæ and canaliculi are black; but when seen by dark-field -illumination the Haversian canals become black, and the lacunæ are -white. - -As these canaliculi exist equally in every direction, it is impossible -to make a section of bone without cutting myriads of them across; and -when a high power is employed they look like little dots scattered over -the surface. A very pretty object can be made of the bone taken from a -young animal which has been fed with madder, as the colour gets into -the bone and settles chiefly round the Haversian canal. A young pig is -a very good subject, so is a rabbit. - -Fig. 16 is a similar section cut from the leg-bone of an ostrich. - -The development of bone is beautifully shown in Fig. 30, a delicate -slice taken from a pig’s rib. Above may be seen the gristle or -cartilage, with the numerous rows of cells; below is the formed bone, -with one of the Haversian canals and its contents; while between the -two may be seen the cartilage-cells gathering together and arranging -themselves into form. The cartilage-cells are well shown in Fig. 28, -which is a portion of the cup which had contained the eye of a haddock. - -The horn-like substances at the end of our fingers, which we call the -nails, are composed of innumerable flattened cells. These cells are -generally so fused together as to be quite indistinguishable even with -a microscope, but can be rendered visible by soaking a section of nail -in liquor potassæ, which causes the cells to swell up and resume to a -degree their original rounded form. - -It is worthy of remark that the animal form is built up of cells, as is -the case with the vegetables, although the cells are not so variable -in shape. They generally may be found to contain well-marked nuclei, -two or more of the latter being often found within a single cell, and -in many cases the tiny nucleoli are also visible. Good examples of -these cells may be obtained from the yolk of an egg, and by careful -management they may be traced throughout every part of the animal form. - -The teeth have many of the constituents of bone, and in some of their -parts are made after precisely the same fashion. When cut, the teeth -are seen to consist of a hard substance, called enamel, which coats -their upper surfaces, of dentine, or ivory, within the enamel, and of -“cement,” which surrounds the fangs. In Fig. 26, Plate X., which is -a longitudinal section of the human “eye” tooth, is seen the ivory -occupying the greater part of the tooth, coated by the enamel at the -top and the cement at the bottom. In the centre of each tooth there is -a cavity, which is plentifully filled with a pulpy substance by which -the tooth is nourished, and which conveys the nerves which endow it -with sensation. A traverse section of the same tooth is seen in Fig. 25. - -The enamel is made of little elongated prisms, all pointing to the -centre of the tooth. When viewed transversely, their ends are of a -somewhat hexagonal shape, something like an irregular honeycomb. The -dentine is composed of a substance pierced with myriads of minute -tubes. They require a rather high power--say 300 diameters--to show -them properly. The cement is found at the root of the fangs, and is -best shown in the tooth of an aged individual, when it assumes very -clearly the character of bone. - -Sections may be made by sawing a slice in the required direction, -polishing one side, and cementing it with old Canada balsam to a slide. -It may then be filed down to nearly the required thinness, finished by -carefully rubbing with a hone, and polished with buff leather. Canada -balsam may then be dropped upon it, and a glass cover pressed firmly -down. - -Sections of young bone form magnificent objects for the polariser. - -Fig. 29 is a section cut from one of the palate teeth of the ray -(_Myliobátes_). - -A rather important element in the structure of animals is the “elastic -ligament,” which is found in the back of the neck and other parts of -the body, especially about the spine. It is made of a vast number of -fibres of variable shape and length, branching and communicating, -arranged generally in bundles, and remarkable for containing very few -vessels, and no nerves at all. At Fig. 14 may be seen an example of -elastic ligament, popularly called “paxwax,” taken from the neck of a -sheep. - -The white fibrous tissue by which all the parts of the body are bound -together is seen at Fig. 10; and at Fig. 11 is a beautiful example of -the “ultimate fibres” of the crystalline lens of a sturgeon’s eye. - -The muscles of animals are of two kinds, the one termed the striped, -and the other the unstriped. Of these, the latter belongs to organs -which work independently of will, such as the stomach, etc., while -the former belongs to those portions of the body which are subject to -voluntary motion, such as the arm and the leg. The unstriped muscle -is very simple, consisting merely of long spindle-shaped cells, but -the striped or voluntary muscle is of more complex construction. Every -voluntary muscle consists of myriads of tiny fibres, bound together in -little bundles, enveloped in a kind of sheath. Fig. 24 is an example of -this muscular fibre, taken from beef. When soaked in spirit, it often -splits into a number of discs, the edges of which are marked by the -transverse lines. - -A fibre of nerve is drawn at Fig. 23, and is given for the purpose of -showing the manner in which the nerve is contained in and protected -by its sheath, just like a telegraph-wire in its coverings. Just -above is a transverse section of the same fibre, showing the same -arrangement from another point of view, and also illustrating the -curious phenomenon, that when nerve-fibres are treated with carmine the -centre takes up the colouring matter, while the sheath remains white as -before. The best way of studying nerves is to decapitate a frog, and -cut off a piece of one of the nerves, which, like fine silk threads, -come out between the joints of the spine inside the abdomen. By careful -teasing out it is easy to obtain preparations showing all the above -points, and, in addition, the folding-in of the internal sheath which -correspond to the insulators of a telegraph-line. - -The blood of animals is analogous in its office to the sap of plants, -but differs greatly from it under the microscope. In sap there seem to -be no microscopic characters, except that when a branch is cut, as in -the vine, the flowing sap may contain certain substances formed in the -wounded cells, such as chlorophyll, starch, and raphides; but the blood -is known to be an exceedingly complex substance both in a microscopic -and a chemical point of view. When a little fresh blood is placed under -the microscope, it is seen to consist of a colourless fluid filled with -numerous little bodies, commonly called “blood-globules,” varying very -greatly in size and shape, according to the animal from which they -were taken. Those of the reptiles are very large, as may be seen at -Fig. 4, Plate X., which represents a blood corpuscle of the Proteus. -In this curious reptile the globules are so large that they may be -distinguished during its life by means of a common pocket lens. - -In the vertebrated animals these corpuscles are red, and give to the -blood its peculiar tint. They are accompanied by certain colourless -corpuscles, spherical in form, which are sometimes, as in man, larger -than the red globules, and in others, as in the siren and the newt, -considerably smaller. The general view of the red corpuscles has -sufficient character to enable the practised observer to name the -class of animal from which it was taken, and in some cases they are -so distinctive that even the genus can be ascertained with tolerable -certainty. In point of size, the reptiles have the largest and the -mammalia the smallest, those of the Proteus and the musk-deer being -perhaps the most decidedly opposed to each other in this respect. - - -IX. - - FIG. - 1. Amœba diffluens - 2. Arcella - 3. Sun animalcule - 4. Miliolina - 5. Paramœcium - 6. Chilodon subdividing - 7. Melicerta ringens - 8. Spicula of Sponge, Grantia - 9. Noctiluca miliaris - 10. Rotifer vulgaris - 11. Do. jaws - 12. Sponge animalcule - 13. Sertularia operculata - 14. Sponge, Grantia - 15. Sertularia operculata, with ovicells - 16. Actinia, showing weapons - 17. Do. base of weapon more magnified - 18. Sponge granule, ciliated - 19. Anguinaria anguina - 20. Spicules of sponge from Oyster Shell - 21. Head of Snake-headed Zoophyte - 22. Bugula avicularia - 23. Polyzoön, Eretea - 24. Do. Notamia - 25. Zoea, Young of Crab - 26. Hydra tuba - 27. Medusa, cast off from above - 28. Naked-eyed Medusa, Thaumantias - 29. Compound Eye, Medusa - 30. Larva, Snake Star - 31. Water Flea - 32. Serpula, Pushing Pole - 33. Comatula, early stage of Starfish - 34. Carbonate of Lime, artificial - 35. Sea Urchin, transverse section of spine - 36. Serpula, bundle of spears - 37. Sun-star, part of skin - 38. Oyster shell in different stages - 39. Cilia on mussel - -[Illustration: IX.] - -In shape, those of the mammalia are circular discs, mostly with a -concave centre, though the camel has oval ones; those of the birds are -more or less oval and convex; those of the reptiles are decidedly oval, -very thin, and have the nucleus projecting; and those of the fishes are -oval and mostly convex. During the process of coagulation the blood -corpuscles run together into a series of rows, just as if a heap of -pence had been piled on each other and then pushed down, so that each -penny overlaps its next neighbour. - -These objects are illustrated by six examples on Plate X. Fig. 2 is -human blood, showing one of the white corpuscles; Fig. 3 is the blood -of the pigeon; Fig. 4, of the _Proteus anguínus_; Fig. 5, of the -tortoise; Fig. 6, of the frog, showing the projecting nucleus; and -Fig. 7, of the roach. The blood possesses many curious properties, -which cannot be described in these few and simple pages. - -In the centre of Plate X. is a large circular figure representing -the membrane of a frog’s foot as seen through the microscope, and -exhibiting the circulation of the blood. The mode of arranging the foot -so as to exhibit the object without hurting the frog is simple enough. - -Take an oblong slip of wood,--my own was made in five minutes out of -the top of a cigar-box,--bore a hole about an inch in diameter near -one end, and cut a number of little slits all round the edge of the -wooden slip. Then get a small linen bag, put the frog into it, and dip -him into water to keep him comfortable. When he is wanted, pull one of -his hind feet out of the bag, draw the neck tight enough to prevent -him from pulling his foot back again, but not sufficiently tight to -stop the circulation. Have a tape fastened to the end of the bag, and -tie it down to the wooden slide. Then fasten a thread to each of his -toes, bring the foot well over the centre of the hole, stretch the toes -well apart, and keep them in their places by hitching the threads into -the notches on the edge of the wooden strip. Perhaps an easier plan -is to secure the threads by drops of sealing-wax when in the desired -position. Push a glass slide carefully between the foot and the wood, -so as to let the membrane rest upon the glass, and be careful to keep -it well wetted. If the frog kick, as he will most likely do, pass a -thin tape over the middle of the leg, and tie him gently down to the -slide. - -Bring the glass into focus, and the foot will present the appearance -so well depicted in the engraving. The veins and arteries are seen -spreading over the whole of the membrane, the larger arteries being -often accompanied by a nerve, as seen in the illustration. Through all -these channels the blood continually pours with a rather irregular -motion, caused most probably by the peculiar position of the reptile. -It is a most wonderful sight, of which the observer is never tired, -and which seems almost more interesting every time that it is beheld. - -The corpuscles go pushing and jostling one another in the oddest -fashion, just like a British crowd entering an exhibition, each one -seeming to be elbowing its way to the best place. To see them turning -the corners is very amusing, for they always seem as if they never -could get round the smaller vessels, and yet invariably accomplish the -task with perfect ease, turning about and steering themselves as if -possessed of volition, and insinuating their ends when they could not -pass crosswise. - -By putting various substances, such as spirit or salt, upon the -foot, the rapidity of the circulation at the spot can be greatly -increased or reduced at will, or even stopped altogether for a while, -and the phenomenon of inflammation and its gradual natural cure be -beautifully illustrated. The numerous black spots upon the surface are -pigment-cells. - -The tails of young fish also afford excellent objects under the -microscope, as the circulation can be seen nearly as well as in the -frog’s foot. The gills of tadpoles can also be arranged upon the stage -with a little care, and the same organs in the young of the common newt -will also exhibit the circulation in a favourable manner. The frog, -however, is perhaps the best, as it can be arranged on the “frog-plate” -without difficulty, and the creature may be kept for months by placing -it in a cool, damp spot, and feeding it with flies, little slugs, and -similar creatures. - - - - -CHAPTER VIII - - Pond-Life--Apparatus and Instructions for Collecting Objects--Methods - of Examination--Sponge--Infusoria. - - -Of all departments of microscopic research the most fascinating and -the most popular is that which deals with what is known by the generic -name of “pond-life.” The minute forms of the animal creation included -in this term are of such exquisite beauty, and allow the processes of -their life-history to be followed with such facility, from the cradle -(when they have one) to the grave (which is very often the body of -another, larger, organism), that there is none which has attracted -more observers. Indeed, the first application of the microscope, by -Leeuwenhoek, early in the seventeenth century, was to the observation -of these forms of life. - - -X. - - FIG. - 1. Skin, Frog - 2. Blood, Human - 3. Do. Pigeon - 4. Do. Proteus - 5. Do. Tortoise - 6. Do. Frog - 7. Do. Fish - 8. Human nail - 9. Bone, Human - 10. White fibrous tissue - 11. Epithelial cells from tongue - 12. Feather, Peacock - 13. Spine, Hedgehog, transverse section - 14. Pax-wax - 15. Epithelial cells from nose - 16. Bone, Ostrich - 17. Feather, Shaft of Canary’s - 18. Do. Wild Duck - 19. Circulation of blood, Frog’s foot - 20. Feather, Sparrow - 21. Do. Cock’s tail - 22. Fibre, crystalline lens of fish - 23. Nerve - 24. Muscle, Meat - 25. Tooth, transverse section - 26. Do. Longitudinal section - 27. Sweat duct - 28. Eye of Haddock - 29. Myliobates, palate - 30. Gristle, Pig - 31. Pigment, Human eye - 32. Do. Wing of Bat - 33. Do. Shell of Prawn - -[Illustration: X.] - -A few words may be said, in the first place, as to the outfit. A very -useful part of it is a walking-stick, to which can be attached either -a net for capturing the larger forms of life, or a hook for collecting -the weeds, to which many forms of great interest and beauty are -attached (Fig. 15). The stick is telescopic, and can also have attached -to it a bottle, which, put into the water at any desired spot,--say, -amongst a clump of weeds, or near the bottom, upside down, and then -suddenly reversed,--will bring away samples of the inhabitants of the -neighbourhood. When these are sparsely distributed through the water, -the latter may be concentrated by the use of a bottle round the neck of -which is firmly tied a coarse calico bag, funnel-shaped, and supported -by a wire ring, somewhat as shown in the illustration. Muslin is, -however, too coarse for many organisms. This net is immersed in the -water so that the ring is just above the surface, and one bottleful -after another poured through. The water strains off, the organisms are -left behind. The immersion is necessary to reduce the pressure to which -delicate organisms would otherwise be subjected. When the bottle is -full, or sufficiently concentrated as to its contents, the latter are -poured into one of the ordinary collecting-bottles, of which half a -dozen at least should always be taken. - -[Illustration: Fig. 15.] - -On reaching home, and as often as possible on the way, the corks should -be removed, as these organisms soon use up the air in the water. - -For examination a glass trough of considerable size, say three inches -in length, half an inch in depth, and two inches in height, should be -half filled with the water, and examined with the pocket magnifier. -With a little practice it will be found easy to take up not only -the larger organisms, but even very minute ones, with one of the -dipping-tubes with a long tapering point already referred to. The -organism, when “spotted,” is followed by eye and tube, the finger -being held over the mouth of the latter, and at the critical moment -the finger is removed, and the organism swept into the tube by the -in-rushing water. Now wipe off the excess with a clean handkerchief, -“spot” the organism in the tube again, and carefully absorb the -superfluous water with a piece of blotting paper; and finally, gently -but sharply blow the remainder on to the plate of the live-box, put on -the cover, and examine with a one-inch power. If, as often happens, -the organism sticks to the side of the tube, a little more water must -be drawn in, and the process repeated. The use of the cotton-wool trap -spoken of previously will often be very helpful in the examination of -actively moving organisms. - -In the case of weeds, a small portion should be placed in the trough -and carefully examined from end to end, first with the pocket lens and -then with the one-inch power. Let us now consider the objects most -likely to be met with. - -A piece of stick may be coated with a white layer, feeling rough to the -touch, and full of small holes. The chances are that this will be a -piece of fresh-water sponge, _Spongilla fluviatílis_, and by dark-field -illumination particles may be seen to enter at some orifices and be -ejected at others. With a very high power and a very thin section, -properly prepared, these holes will be seen to be the mouths of -channels which are lined by the most delicate organisms possible, each -having a minute body crowned with a tiny crystal cup, in the middle of -which is a long cilium, or flagellum, as it is here called (Plate XIII. -Fig. 1). The currents are produced by the combined action of these -flagella. In point of fact, the sponge is a colony of minute animals -working harmoniously for the common good. If the specimen be found in -winter the sponge will be full of tiny balls, the “gemmules” of the -next season’s growth. The roughness is due to the flinty spicules, -which are at once the scaffolding and the protection of the sponge, and -by boiling the sponge in a mixture of nitric acid and water (half and -half) these spicules will be set free, and may be washed, allowed to -settle, washed again, dried, and mounted in balsam. The gemmules are -coated by very beautiful spicules, consisting of two wheels connected -by a rod. These may be treated in the same way. The life-history of the -common sponge is as yet but imperfectly known. - -Perhaps the lowest form of life is the _Amœba_, shown in Plate IX. -Fig. 1, a mere lump of jelly, which flows along, and when it comes -into contact with any likely subject for digestion flows round it, -encloses it, absorbs what it can from it, and leaves it behind. A near -relative of the Amœba is the _Arcella_ (Fig. 2), which is simply an -Amœba with a shell. Being unable to swim, these organisms are naturally -to be most often found at the bottom of the collecting bottle, and -it is always advisable to take up a portion of the débris with a -dipping tube, which is then held upright on a slide with the finger -upon it until the dirt settles on to the slide, when it is removed, -a cover-glass put upon the dirt, and a quarter-inch power used for -examination. Many forms will be discovered in this way which would -otherwise escape observation. - -Another curious organism, of great size (comparatively) and extreme -beauty, is the sun animalcule (_Actínophrys_), which has a round body -and long tentacles (Fig. 3), to which free-swimming organisms adhere, -and by the combined action of the neighbouring ones are drawn to the -body and received into it; one cannot say swallowed. - -Fig. 6, Plate IX., shows the curious arithmetical process whereby -the Infusoria multiply by division, a groove appearing at one point, -rapidly deepening, and finally separating the animal completely into -two. The species is the _Chílodon_, a flattened creature, ciliated all -over, having a set of teeth arranged in the form of a tube, and at its -fore-part a kind of membranous lip. A similar phenomenon, in an earlier -stage, is shown in Fig. 26, Plate XIII., the organism in this case -being _Euplótes_. - -It has been said that sponges are colonies of extremely minute -organisms, each furnished with a membranous collar or funnel, the whole -looking like an exquisite wine-glass without a foot. These organisms -are not always grouped in colonies, however. Many are free-growing, -and may be found attached to the stems of water-plants, but they are -extremely minute, and will hardly be noticed until the microscopist -has acquired considerable experience, nor even then--with such an -instrument as we have postulated--will he see more than a tiny pear, -with a straight line, the margin of the cup, on each side of its -summit. The flagellum will be quite invisible. - -Some similar organisms may, nevertheless, be found which, though -still minute, are within the range of a properly managed quarter-inch -objective. Such an one, of extreme beauty, is the _Dinobrýon_ shown in -Plate XIII. Fig. 3. Each “zoöid,” as the separate animals are called, -among the Infusoria, or each generation of zoöids, stands upon its -parent and has two flagella. When alarmed, the zoöid sinks to the -bottom of its cell, and withdraws its flagella. In Fig. 2 (_Eugléna_) -we have a similar zoöid, but of far greater size, and free-swimming. -It is a very common object, and possesses a red eye-speck close to the -“contractile vesicle.” All Infusoria have the latter, some a great -number, as in Fig. 9. The vesicle contracts at regular intervals, and -is then simply blotted out, but reforms in the same place, so that it -is probably the heart or the urinary bladder of these minute animals. - -The lovely rosette shown in Fig. 4 is the _Synura_, a spherical colony -of zoöids, each of which has two flagella, and is in addition clothed -with rows of cilia. A beautiful sight it is to watch these colonies -rolling through the field of view. Not uncommon, especially in brackish -water, is the _Peridinium_ (Fig. 5), with its plate armour, long -flagellum, and girdle of cilia. A gigantic species of the same family -is common in sea-water, and will be easily recognised by its body, not -much larger than that of Peridinium, being furnished with three long -arms, curiously bent. It is called _Ceratium_, and is sometimes present -in such abundance as to thicken the water, near the surface of which it -swims. - -We now come to a class of Infusoria which is characterised by the -possession of a complete covering of cilia, arranged in rows all over -the body. The number of these is enormous; we can only glance at a -few types, by mastering which the observer will, at all events, know -whereabouts he is. The first we will take is the _Coleps_ (Fig. 6), -a very common kind, whose body is marked by a series of geometrical -lines, so that the organism looks very much like an elongated -geographical globe. These markings are on the tunic, which is of a -brownish colour. Very different is the _Trachelocerca_ (Fig. 7), with -its long flexible neck, which is in constant movement from side to side -as the creature swims along. As seen in the figure, the neck is clear -and the head has a fringe of longer cilia. - -The _Trachelius_ (Fig. 8) is perhaps the largest of all the Infusoria, -being readily visible to even an inexperienced eye. Its body is richly -furnished with contractile vesicles, and the protoplasm is curiously -reticulated. We may here remark that the Trachelius is especially -prompt in doing what most of these organisms do when put under pressure -in a live-box, namely, in performing a kind of _harakiri_. The outline -first becomes irregular, then the body rapidly swells and finally comes -to pieces, the fragments dancing mockingly away under the influence of -their still-moving cilia. The remedy is to use the cotton-wool trap and -the lightest possible pressure. - -A very elegant organism is shown in the bottom right-hand corner of the -Plate (Fig. 25). It is the _Loxophyllum_, and has a strongly marked -contractile vesicle. - -Another large form is _Amphileptus_ (Fig. 9), already referred to as -having a large number of contractile vesicles arranged in a regular -row; and more massive still is _Bursaria_ (Fig. 10), a very curious -organism, very much like a purse indeed, and possessing a wonderful -arrangement of cilia inside the funnel. These are arranged like a -ladder, a series of rows of short stiff cilia, which move at short -intervals in unison, and tend to sweep down into the cavity any -small particles of food. This arrangement is here described for the -first time, and appears to be quite unlike anything else among the -Infusoria. Not unlike Bursaria, but having no ladder, and being -furnished with a delicate membranous pouch in front of the slit of the -purse, is _Condylostoma_, which we shrewdly suspect to be the young -form of Bursaria. This is a point which requires elucidation. - -One of the most beautiful of all these forms is shown in Fig. 11, -_Folliculina_, a type of a large group characterised by the possession -of a transparent case, of extremely elegant form, within which the -animal retreats on the slightest alarm. - -Fearless and independent, as becomes its size, is the trumpet-shaped -_Stentor_ (Fig. 12), which may easily be seen when present, as it is in -almost every good gathering of water-weed. The particular form drawn -(_S. Mülleri_) does not make a case, but many members of the genus -do, and it is very common to see a stem almost covered with them. -Such a sight, once seen under dark-field illumination, will never be -forgotten. The method of multiplication of the Stentors (by division) -is extremely easy to watch, and very instructive. - -A curious organism is _Trichodina_ (Fig. 13), which, though a -free-swimmer, is always parasitic upon the body of some higher animal. -We have found it sometimes upon Hydra, and always in hundreds upon the -stickleback. The next group of Infusoria is distinguished by the body’s -being only ciliated at particular points, usually round the mouth, or -what acts as such. The first form is Vorticella (Fig. 14), a beautiful -vase-like creature upon a stem. Down the stem runs a muscular fibre, -and on the least shock the fibre contracts and draws the stem into a -beautiful spiral, whilst the cilia are drawn in, and the zoöid assumes -the appearance of a ball at the end of a watch-spring. An exquisite -sight is a colony of Vorticellæ, for these actions are always going on, -as, for example, when one member of the family touches another, which -is quite sufficient to provoke the contraction. - - -XI. - -POLARIZED LIGHT. - - FIG. - 1. Carbonate of Lime - 2. Starfish - 3. Thistle down - 4. Starch, Wheat - 5. Do. Potato - 6. Prawn-shell - 7. Starch, “Tous les mois” - 8. Bone, cancellous - 9. Gun-cotton - 10. Cow’s hair - 11. Hoof, donkey, longitudinal - 12. Do. transverse - 13. Nitre, Crystals - 14. Scale, Eel - 15. Wing, Water-Boatman - 16. Chlorate of Potash, Crystals - 17. Cellularia reptans - 18. Star-shaped hair, Stalk of Yellow Water-Lily - 19. Teeth, Palate of Whelk - 20. Zoophyte, Bowerbankia - 21. Raphides, _i.e._ crystalline formations in - vegetable cells, Bulb of Hyacinth - 22. Do. Rhubarb - 23. Sulphate of Magnesia, Crystals - 24. Bone, Skate - 25. Cherrystone, transverse section - 26. Sugar, Crystals in honey - 27. Tendon, Ox - 28. Calcareous plates. Tooth of Echinus - -[Illustration: XI.] - -Many compound tree-like forms of Vorticella are known, one of which, -_Carchesium_ (Fig. 15), may serve as a type of all. In the case of this -organism, the colony contracts in sections on a moderate shock; in the -second, _Zoothamnium_, as a whole; whilst in _Epistylis_ the stalks are -rigid, and the individuals contract singly. When the shock is violent, -the appearance presented by the two former is that shown in Fig. 16. In -all three cases the colonies are usually so large that they are visible -as trees to the naked eye, and some members of the group are extremely -common. Moreover, they are often parasitic, as, for example, upon -Cyclops, which is frequently loaded with them. - -Another compound form is _Ophrydium_, a colony of which (not unusually -large) is shown of the natural size in Fig. 18, with a single zoöid, -magnified, by the side of it, in Fig. 19. - -Lastly, we have an exquisite group of organisms related to Vorticella, -but possessing a transparent envelope, the forms of which are most -varied, but always graceful. _Vaginicola_ (Fig. 17) is a good example -of this, and _Cothurnia_ (Fig. 20) still more so. Many of these -organisms, too, are furnished with a plate, attached either to the -head or to the body, which plate, when they withdraw into their cases, -closes the latter perfectly, as in the case of the exquisite _Pyxicola_ -(Fig. 21). - -A very interesting but singularly obtrusive organism is the -_Stylonychia_ (Figs. 22, 23). How often has it happened to us to have -an interesting object nicely in the field of view, and then to have it -knocked out of sight by the blundering incursion of this burly fellow, -who runs so rapidly by means of his “styles” that he gives nothing -time to get out of the way. He is of interest to us, however, as the -representative of a class in which the body is not ciliated, or very -partially and slightly so, usually round the mouth. We have frequently -found Stylonychia, in company with Vorticella and _Paramœcium_ (Plate -IX. Fig. 6), in the water in which flowers have been standing for a few -days; sometimes the numbers are so great as to make the water quite -milky. - -One more form must conclude this short sketch of the great Infusorial -family. It is the _Acineta_ (Fig. 24), which, attached by its -foot-stalk, and devoid of cilia, patiently waits, with outspread arms, -to receive and embrace smaller members of the family as they dance -merrily about. Alas! its embrace is as fatal as that of the image of -the Virgin which bore beneath its robe spikes and daggers, for the -victim struggles vainly to escape, and the nourishment from its body is -rapidly absorbed. - -And here we take our leave of a group which, simple as is the -construction of the animals which it includes (for every one, great -and small alike, is composed of a single cell), is yet full of beauty -and interest. He who wishes to pursue the matter further will find in -Saville Kent’s _Manual of the Infusoria_ a perfect mine of information, -to which we gladly acknowledge our indebtedness, both now and in time -past. - - - - -CHAPTER IX - - Fresh-water Worms--Planarians--Hydra--Polyzoa--Rotifers--Chætonotus-- - Water-Bears. - - -The fresh-water worms form a large and well-defined group, and a few -words regarding them may be useful. - -They are very common, and very difficult to find information about, -most of the work relating to them having been done in Germany. At the -same time, they are so highly organised and so transparent that the -process of their life-history may be easily followed. - -One large group has the peculiarity of multiplying by division, the -last joints or segments being devoted to the formation of the new -individual. At one time of the year the ordinary sexual process of -reproduction takes the place of this method, and each worm is then -surrounded by a belt such as may be seen in the common earthworm under -similar conditions. Further information on this subject is greatly -needed. - -The type is the common _Naïs_, which has a body of thirty segments or -more, two eye-specks on the head, and a double row of bristles along -the back; whilst below, each segment carries strong hooked bristles, -nearly buried in the body, by means of which the worm crawls. Inside -the mouth is a large proboscis, which can be protruded, and this leads -into a stomach which is merely an enlargement of the intestine which -succeeds it. The circulation of the blood (which is colourless) can be -easily watched. It begins at the tail with a contraction of the dorsal -vessel, passes up to the head, and then down below the intestine to the -tail again. The intestine is ciliated inside, and it is by a current -of water carried into the intestine by these cilia that the blood is -aërated. - -In the next genus, _Dero_, this is clearly seen, for the tail (Plate -XIV. Fig. 1) is opened out into a wide shield, from which rise four, -six, or even eight finger-like processes. These parts are all ciliated, -and contain a network of blood-vessels. The worm lives in a case which -it builds in the mud, and the way to find it is to put some of the mud -into a glass beaker with water, and allow it to stand. If there be -members of this family in it, their tails will be seen protruding above -the water. Pour out the mud sharply, fill up with water, and allow the -dirt to subside, and the worms may then be made to leave their cases by -pressure by a camel hair pencil on the lower end of the tube, and may -be caught with the dipping tube and placed in the live-box. They have -no eyes, otherwise the general outline of the body closely resembles -that of Naïs. - -_Slavína_ (Fig. 2) has a row of touch-organs, like pimples, round -each segment, and is a dirty looking creature, with an inordinately -long first pair of bristles, but this reaches its acme in _Pristina_ -(Fig. 3) (sometimes, though wrongly, called _Stylaria_) _parasita_, -which has three long sets of bristles upon the back, and keeps these in -constant wing-like motion. The true _Stylaria_ has a long trunk, set -right in the head, and tubular (Fig. 6); it grows to a considerable -length, and when in the stage of fission it is very funny to see -the two proboscides waving about, one on the middle, as well as the -original one at the head. There is also a form with a shorter proboscis -of the same kind. - -_Bohemilla_ has a tremendous array of saw-like bristles upon the back, -whilst _Chætogaster_ has none at all in this position, and few below. -_Æolosoma_ has merely tufts of hair instead of bristles, and swims -freely. It is easily recognised by the red, yellow, or green pigment -spots in its skin, and by the ciliated head. Rarest of all the family -is the one which connects it with the ordinary _Tubifex_, the red worm -which lives in masses in the mud of brooks and ponds, the waving tails -protruding above the water, and being instantly withdrawn when a foot -is stamped upon the bank. Their Naid cousin is _Naidium_, and has red -blood, but multiplies by fission, which Tubifex does not. - -Another group of worms is the _Planarians_, small leech-like worms, -black, white, or brown, which are rarely absent from a gathering. The -would-be investigator will find in them an abundant field for work, as -they are but very imperfectly known or studied. - -The great enemy of all these worms is the _Hydra_, a good idea of -which may be formed from Plate IX. Fig. 13. There are three species, -all of which are fairly common. They capture their prey in exactly the -same way as sea-anemones and the marine hydroid forms, so numerous and -varied. - -Nor must we omit to notice the exquisitely beautiful Polyzoa, such -as _Lophopus_ (Plate XIV. Fig. 4), with its ciliated tentacles and -transparent social home; _Fredericella_ (Fig. 5), with its graceful -stems, and their still more graceful inhabitants; and the wonderful -_Cristatella_, whose colonies form bodies which crawl over the stems -of water plants. But for grace, beauty, and variety, the Rotifers -assuredly outshine all their fellow inhabitants of our ponds and -streams. - -We can only take a few types, and of all these the most common is the -common Rotifer (Plate IX. Fig. 10). It is there shown in the act of -swimming, but it can withdraw its “wheels” and creep like a leech, -protruding its foot as it does so. It is distinguished by the two -eye-spots on the proboscis from _Philodina_, in which they are on the -breast, and _Callidina_, which has none. When at ease in its mind, the -animal protrudes its wheels, and by their action draws in particles -of food, these passing down to the incessantly moving jaws, which act -like a mill and crush the food before it passes on to be digested. The -movement of the jaws may even be seen in the young Rotifer whilst still -in the egg within the body of the parent, and as the egg reaches its -full development other eggs again are visible within it, so that we may -have three generations in one individual. The males of most of the -Rotifera are unknown. Those that are known are very lowly organised, -having only the ciliary wreath and the reproductive organs, and are -only found at certain seasons of the year. For the remainder of the -time parthenogenesis is the rule, just as among the Aphides. We select -a few individuals for illustration as types. Those who wish to pursue -this study further must be referred to the monumental work of Hudson -and Gosse. - -The common Rotifer, already referred to, may be taken as the type -of the Bdelloida, or leech-like class, so called from their mode of -“looping” themselves along. The group is a comparatively small one in -comparison with the next, the Ploïma, or free-swimmers. We can only -select from the vast variety a few species, first of those classed -as illoricated, from their being without a _loríca_, or case, and -then of the loricated, which possess it. A very large and common -form is _Hydátina_ (Plate XIV. Fig. 7), which lives by choice in the -reddish pools of water found often by the roadside. It shows the whole -organisation of the class magnificently; the ciliary wreath on the -head, with the striped muscles which draw the latter back, the powerful -jaws, the digestive canal with its crop and intestine, the ovary -with the developing eggs, the water-vascular system with the curious -vibratile tags, and finally, the cloaca, which receives the waste of -the body and expels it at intervals. - -Another form, also common, especially in clear water, is _Synchæta_ -(Fig. 8), very much like a kite or peg-top in shape, which has the -power of attaching itself by a glutinous thread, and spinning round at -a tremendous rate. Then there is the gigantic _Asplanchna_ (Fig. 9), -which has no opening below, so that the waste must be discharged by the -mouth; and curious _Sacculus_, which gorges itself with chlorophyll -until it looks like a green bag with a string round it, but clear and -sparkling. Of the _Notommatæ_ there is a whole host, but we can only -mention the beautiful _N. Aurita_ (Fig. 10), with an eye of a beautiful -violet colour, composed of several spherules massed together, and two -curious ear-like processes on the head, from which it takes its name. -Some of the Ploïma have powers of leaping which must be noticed. The -_Triarthra_ (Fig. 11) has three arms, or what we may call such, which -it can stretch out suddenly and leap to a considerable distance, whilst -in _Polyarthra_ the arms become a whole cluster of broad saw-like -bristles. - -We pass on to note a few species of the mail-clad or loricated -Rotifers, chief among which the great _Euchlanis_ (Fig. 12), a -noble-looking fellow, calls for our attention, his great size rendering -him easily visible to the naked eye. It is difficult to avoid using the -masculine gender, but, of course, all those figured and described are -of the gentler sex. _Salpina_, too (Fig. 14), with its box-like lorica, -armed with spines at each of the upper angles, and having three below, -is quite easily recognised, and very common. _Brachionus_ (Fig. 13) -has a shield-shaped case, well furnished with spines, symmetrically -arranged at the top, and an opening below for the flexible wrinkled -tail, like the trunk of an elephant. _Pterodina_ (Fig. 15) has a -similar tail, but a round case, and the head is much more like that -of the common Rotifer when extended. _Anuræa_ (Fig. 16), on the other -hand, has no tail, and its case is shaped like a butcher’s tray, with -a handle at each corner. _Dinocharis_ (Fig. 17) has a roof-like case, -with long spines on the root of the tail, and a forked stiff foot. -_Noteus_ (Fig. 18) is much like Pterodina, except in its foot, which -more nearly resembles that of Dinocharis. - -The list might be indefinitely extended, but sufficient has probably -been said to enable the tyro to find his bearings in this large, -beautiful, and interesting class. - -We pass on to notice in conclusion two or three of the fixed forms, -of which a beautiful example is the _Melicerta ringens_ (Plate IX. -Fig. 7), whose building operations have a never-ending charm. Particles -of débris are accumulated in a curious little cavity in the chin, in -which they are whirled round, and mixed with a secretion which binds -them together, and when a brick is made the head is bent down and the -brick applied to the desired spot with mathematical regularity. By -supplying fine particles of innocuous colouring matters, the Melicerta -may be made to build a variegated case. The most remarkable specimen -known is the one figured in Hudson and Gosse’s work, which was found -by the present writer in a specimen of water from which he had already -obtained five-and-twenty species of various kinds of Rotifer; the water -was collected by an inexperienced person, and there was only a pint -of it. It had, moreover, been kept for three weeks, and the moral of -that is, to preserve one’s gatherings, and keep an aquarium into which -they may be poured when done with for the moment. New forms will often -develop with startling rapidity, their eggs having been present in the -original gathering. The young form of Melicerta, shown in Plate XIV. -Fig. 20, is strangely unlike its mother, and much more nearly resembles -its father. - -Another group of extreme beauty is the Flosculariæ (Fig. 19), several -species of which are very common. They will be easily known by their -appearance, which resembles a shaving brush when closed; whilst, when -opening, the shaving brush resembles a cloud of delicate shimmering -threads, which at last stand out straight, radiating all round the head -of the creature, and forming the trap by means of which it catches its -prey. Finally, there is the lovely _Stephanoceros_ (not, unfortunately, -very common), with its five symmetrically placed and gracefully curved -arms, perhaps the most lovely of all Rotifers, with its exquisitely -transparent body, sparkling with masses of green and golden brown. -He who finds this has a treasure indeed, and will be encouraged to -prosecute his studies in this “Fairyland of Microscopy.” - -Two irregular forms call for a word of remark. The first is -_Chætonotus_ (Plate XIII. Fig. 27), which stands on the borderland of -the Infusoria and the Rotifers, neglected as a rule by the students -of both; and the second the _Tardigrada_ (Plate XIV. Fig. 21), or -water-bears, which have feet like those of the red wriggling larva of -_Chironomus_, whose silky tubes are common enough on submerged walls -and on the stems of plants, these feet consisting of a mass of radially -arranged hooklets, which can be protruded or withdrawn at will; whilst -the head of the water-bear is far more like that of a louse, pointed -and hard, and suited for burrowing about, as the animal does, among the -rubbish at the bottom of the bottle. Both the genera just referred to -will repay careful study, as little is known of their life-history or -development. - -A few words must be devoted, in conclusion, to the Entomostraca, -those shrimp-like animals which, like their marine relatives, act as -scavengers to the community. Fig. 22 is a portrait of _Cypris_, a not -very handsome form, but one very commonly found. Its shell is opaque, -so that the internal organs are difficult to observe. Far different -in this respect is the beautiful _Daphnia_, the water-flea _par -excellence_, whose carapace is of crystalline clearness, so that every -movement of every one of the internal organs may be followed with the -greatest facility. There are many species of the genus, and some of -them are very common, so that the opportunity of examining these lovely -objects is easily obtained. Plate XIV. Fig. 23, shows the most common -of all the class under notice, the _Cyclops_, so named from the fact -that, like the fabled giants of classical literature, it has a single -eye in the middle of its forehead. It is often loaded with Infusoria, -especially Vorticella and Epistylis, already described, to such an -extent that its movements are greatly hampered. - - -XII. - - FIG. - 1. Tubercle, Sun-star - 2. Zoophyte, Gemellaria - 3. Cuttle bone - 4. Plate of ditto from above - 5. Zoophyte, Antennularia - 6. Pedicellaria, skin of Starfish - 7. Shell, Foraminifer - 8. Snake-star, disc from below - 9. Pedicellaria, Echinus - 10. Wing-case, Weevil - 11. Coralline - 12. Spine, Echinus - 13. Foraminifer, Polystomella - 14. Do. Truncatulina - 15. Do. Polymorphina - 16. Do. Miliolina - 17. Gold dust, with quartz - 18. Foraminifer, Lagena vulgaris - 19. Pouches, Skin of Rat’s tail - 20. Foraminifer, Biloculina ringens - 21. Ore, Copper - 22. Zoophyte, Membranipora pilosa - 23. Human skin, injected - 24. Coal, Longitudinal section - 25. Do. Transverse section - 26. Lung, Frog - -[Illustration: XII.] - -We have not space to figure more of these creatures, but other forms -will be found not inferior in interest to those mentioned. The most -curious of all are those which earn a dishonest and lazy living by -attaching themselves to the bodies of other and larger animals, chiefly -fish. One of the largest is the _Argulus_, the bane of aquarium -keepers, which is of considerable size, and attacks gold-fish, and in -fact almost any fish to which it can obtain access. - -The gills of the stickleback will furnish examples of the curious -_Ergasilus_, which consists chiefly of an enormous pair of hooks and -two long egg-bags, the latter, in varying form, being carried by many -of the Entomostraca. - -Upon the fins of the same fish will be found the remarkable -_Gyrodactylus_, a worm-like animal which attaches itself by a large -umbrella-like foot, in the centre of which are two huge claws. The -head is split down the middle for some distance. We may mention, in -concluding our notice of the external and involuntary guests of the -unlucky stickleback, that its skin is usually frequented by hosts -of the Trichodina described in the last chapter. Of the internal -parasites, want of space forbids us to speak. - - - - -CHAPTER X - - Marine Life--Sponges--Infusoria--Foraminifera--Radiolaria--Hydroid - Zoophytes--Polyzoa--Worms--Lingual Ribbons and Gills of - Mollusca--Star-Fishes and Sea-Urchins--Cuttle-Fish-- - Corallines--Miscellaneous Objects. - - -Great as is the range of objects presented to the student of -fresh-water life, the latter field is limited indeed as compared with -that afforded by the sea. The Infusoria and Rotifers furnished by the -latter are, indeed, much fewer in number and variety, but the vast host -of sponges, polyzoa, hydroids, crustacea, molluscs, ascidians, and -worms, to say nothing of the wealth of vegetable life, renders the sea -the happy hunting-ground of the microscopist. - -Whether it be along the edge of the water, as the tide retreats, -especially after a gale; or in the rock-pools; or, perhaps best of -all, upon those portions of the shore left uncovered only by the -lowest spring-tides, the harvest is simply inexhaustible. Stones -turned up will exhibit a world in miniature. Encrusted with green or -pink sponges, or with gelatinous masses of ascidians, fringed at its -edges with hydroids, coated above with polyzoa, a single one will -often supply more work than could be got through in a week of steady -application. - -A description of the fresh-water sponge already given may serve very -well to indicate the general outlines of the organisation of the marine -ones too. The spicules of the latter are, however, not always flinty; -very often, as in the case of _Grantia_ (Plate IX. Figs. 8 and 14), -they are calcareous, a point which can be settled by the application of -a little nitric acid and water. If lime be present there will be strong -effervescence, and the separation of the spicules can only be effected -by gently warming a portion of the sponge in caustic potash solution, -pouring the resulting mass into water, and allowing the spicules to -settle. The washing and settling must be repeated several times, and a -portion of the deposit may then be taken up with a dipping-tube, spread -upon a slide and dried, and then covered in balsam solution. The forms -are endless, and the same sponge will often supply three or four, or -even more. Among them may be seen accurate likenesses of pins, needles, -marlin-spikes, cucumbers, grappling-hooks, fish-hooks, porters’-hooks, -calthrops, knife-rests, fish-spears, barbed arrows, spiked globes, -war-clubs, boomerangs, life-preservers, and many other indescribable -forms. The flinty forms must be prepared by boiling, as described in -speaking of the mounting of diatoms in Chapter XI., except that, of -course, only one settlement is required after thorough washing. - -Every one who has been by or on the sea on a fine summer night must -have noticed the bright flashes of light that appear whenever its -surface is disturbed; the wake of a boat, for example, leaving a -luminous track as far as the eye can reach. This phosphorescence is -caused by many animals resident in the sea, but chiefly by the little -creature represented at Fig. 9, the _Noctilúca_, myriads of which may -be found in a pail of water dipped at random from the glowing waves. A -tooth of this creature more magnified is shown immediately above. - -A large group of microscopic organisms is known to zoologists under -the name of Foraminifera, on account of the numerous holes in their -beautiful shells, most of which are composed of carbonate of lime, -though some are horny and others are composed of aggregations of minute -grains of sand, the forms in one class often closely imitating those in -another. It is of the shells of these minute animals that the “white -cliffs of old England” are very largely composed, and those who desire -to understand the part which these tiny creatures have played, and are -playing, in geology, will do well to study Huxley’s fascinating essay -on “A Piece of Chalk.” - - -XIII. - - FIG. - 1. Grantia compressa - 2. Euglena viridis - 3. Dinobryon sertularia - 4. Synura uvella - 5. Peridinium tabulatum - 6. Coleps hirtus - 7. Trachelocerca viridis - 8. Trachelius ovum - 9. Amphileptus gigas - 10. Bursaria Mülleri - 11. Folliculina elegans - 12. Stentor polymorphus - 13. Trichodina pediculus - 14. Vorticella nebulifera - 15. Zoothamnium arbuscula - 16. Do. do. contracted - 17. Vaginicola crystallina - 18. Ophrydium versatile (colony) - 19. Do. do. (single zoöid) - 20. Cothurnia imberbis - 21. Pyxicola affinis - 22–23. Stylonychia mytilus - 24. Acineta grandis - 25. Loxophyllum meleagris - 26. Euplotes charon (dividing) - 27. Chætonotus larus - -[Illustration: XIII.] - -The inhabitants of these shells are Amœbæ, mere masses of jelly, -and some forms may be found sliding over the weeds in almost every -rock-pool. The anchor-mud, already spoken of, always contains some, -and many forms may be found in the sand from sponges, which should be -passed through a series of wire sieves, of increasing fineness, and -the residuum in each case be examined dry under a one-inch power. The -shells may be picked up with a needle which has been slightly greased -by being passed over the hair, and they may be mounted by sticking them -to the slide with thin starch paste, putting on a cover-glass properly -supported, and then running turpentine under the cover-glass, heating -to expel the air, and finally filling up with balsam. Or, as opaque -objects, they may be mounted in a cell dry. The forms are endless, but -all are beautiful, and a few examples are given in Plate IX. Fig. 4 -(_Miliolína_), and Plate XII. Fig. 7, which is a portion of the shell -to show the holes, Fig. 13 (_Polystomella_), Fig. 14 (_Truncatulína_), -Fig. 15 (_Polymorphína_), Fig. 16 (_Miliolína_, partly fossilised), -Fig. 18 (_Lagéna_). and Fig. 20 (_Biloculína_). - -Allied to these are the lovely Radiolaria, whose shells, constructed -on a similar plan, are composed of flint. They are found in remarkable -profusion in the deposit from Cambridge, Barbados, but also in a -living state at even enormous depths in the ocean. The present writer -has obtained many forms from _Challenger_ soundings, and the great -authority on this subject is Haeckel’s report in the official accounts -of the expedition of the above-named vessel. - -The Hydroid Zoophytes are represented by several examples. These -creatures are soft and almost gelatinous, and are furnished with -tentacles or lobes by which they can catch and retain their prey. -In order to support their tender structure they are endowed with a -horny skeleton, sometimes outside and sometimes inside them, which is -called the polypidom. They are very common on our coasts, where they -may be found thrown on the shore, or may be dredged up from the deeper -portions of the sea. - -Fig. 13 is a portion of one of the commonest genera, _Sertularia_, -showing one of the inhabitants projecting its tentacles from its -domicile. Fig. 15 is the same species, given to show the egg-cells. -This, as well as other zoophytes, is generally classed among the -sea-weeds in the shops that throng all watering-places. - -The form just referred to is a near relative of the Hydra, already -described, and belongs to the same great family as the sea-anemones. -One form, shown in Fig. 26, is the _Hydra Tuba_, long thought to be a -distinct animal, but now known to be the young form of a jelly-fish, -or Medusa. The Hydra Tuba throws off joints at intervals, each of -which becomes a perfect jelly-fish. One of them is shown in Fig. 27. -Fig. 28 represents a very small and pretty Medusa, the Thaumantias. -When this animal is touched or startled, each of the purple globules -round the edge flashes into light, producing a most beautiful and -singular appearance. Fig. 29 exhibits the so-called compound eye of -another species of Medusa, though it would appear that these are really -connected with the nervous system of the animal, and have to do with -the pulsating contractions of the bell by which it is propelled through -the water. - -In my _Common Objects of the Sea-Shore_ the Actíniæ, or Sea-Anemones, -are treated of at some length. At Fig. 16 is shown part of a tentacle -flinging out the poison-darts by which it secures its prey; and Fig. 17 -is a more magnified view of one of these darts and its case. - -Much more might be said under this head, but we must pass on to another -group, which, whilst possessing a certain general resemblance to the -hydroid zoophytes, differs utterly from them in internal organisation. -We have already referred to the fresh-water polyzoa. The marine forms -are vastly more numerous, and more easily found, since not only -pieces of weed upon which they grow are to be found upon every beach, -but whole masses of leaf-like colonies, forming what is known as -horn-wrack, may be plentifully found. Instead of the tentacles armed -with sting-cells, like the anemone’s, possessed by the Hydrozoa, the -Polyzoa have arms clothed with active cilia, by which the food is swept -into the mouth, passing on into the stomach, and then through the -intestine to another opening. - -Fig. 19 is a very curious zoophyte called _Anguinaria_, or snake-head, -on account of its shape, the end of the polypidom resembling the head -of the snake, and the tentacles looking like its tongue as they are -thrust forward and rapidly withdrawn. Fig. 21 is the same creature -on an enlarged scale, and just below is one of its tentacles still -more magnified. Fig. 23 is the ladies’-slipper zoophyte (_Eretea_); -and Fig. 24 is called the tobacco-pipe or shepherd’s-purse zoophyte -(_Notamia_). - -Fig. 22 is a portion of the _Bugula_, with one of the curious -“birds’-head” processes. These appendages have the most absurd likeness -to a bird’s head, the beak opening and shutting with a smart snap (so -smart, indeed, that the ear instinctively tries to catch the sound), -and the head nodding backward and forward just as if the bird were -pecking up its food. On Plate XII. Fig. 2, is a pretty zoophyte called -_Gemellaria_, on account of the double or twin-like form of the cells; -and Fig. 5 represents the _Antennularia_, so called on account of its -resemblance to the antennæ of an insect. Fig. 22 is an example of a -pretty zoophyte found parasitic on many sea-weeds, and known by the -name of _Membranipora_. Two more specimens of zoophytes may be seen -on Plate XI. as they appear under polarised light. Fig. 17 is the -_Cellularia reptans_; and Fig. 20 is the _Bowerbankia_, one form of -which occurs in fresh water. - -Among the worms we may refer to the beautiful little _Spirorbis_, -whose tiny coiled spiral tube may be found attached to almost every -sea-weed, and which, when placed in a trough of sea-water, protrudes -its beautiful crown of plumes. In chalk or other soft rocks, again, -the tubes of _Spio_, with its two long waving tentacles, may be found -by hundreds. Then there are the centipede-like worms, which may be -found under nearly every stone, and which belong to the great family of -Nereids, provided with formidable jaws and stiff bristles of various -forms. The Serpulæ are allied to the Spirorbis already mentioned. Parts -of the so-called feet of one of these worms are shown in Fig. 36, -where the spears or “pushing-poles” are seen gathered into bundles, as -during life. One of them, on a larger scale, is shown in Fig. 32. The -gorgeous hairs of Aphrodite have already been alluded to. - -In the sea the few species of Crustacea which fresh water offers to -the observer in the shape of Cyclops and its allies become thousands, -and their changes during development are numerous and puzzling. Who, -for example, would suppose that the young stage of the Cyclops was -indistinguishable in habits, and almost in form, from that of the -barnacle which adheres to the rocks? Yet such is the case, and there -are other metamorphoses even more startling. Fig. 25 is the larva of -the common crab, once thought to be a separate species, and described -as such under the name of _Zoæa_. - -The Mollusca proper will not afford us many objects, except in the form -of their lingual ribbon, which may be extracted from the mouth, gently -heated in _liquor potassæ_, and mounted in balsam after well washing, -when the rows of teeth form splendid objects by polarised light. The -palate of a whelk is shown in Plate XI. Fig. 19. - -Again, the gills of the mussel will afford a beautiful illustration of -ciliary action. If a portion of the thin plates which lie along the -edge of the shell be examined in a little of the liquor, the action may -be splendidly seen, and watched for a long time (Fig. 39). - -The structure of shell, _e.g._ oyster-shell, is well shown in three -examples: Fig. 34 is a group of artificial crystals of carbonate of -lime; and on Figs. 38 and 39 may be seen part of an oyster-shell, -showing how it is composed of similar crystals aggregated together. -Their appearance under polarised light may be seen on Plate XI. Figs. 1 -and 6. - -We now pass on to the Echinoderms, including the star-fishes and -sea-urchins. - -The old story of the goose-bearing tree is an example of how truth may -be stranger than fiction. For if the fable had said that the mother -goose laid eggs which grew into trees, budded and flowered, and then -produced new geese, it would not have been one whit a stranger tale -than the truth. Plate IX. Fig. 33, shows the young state of one of -the common star-fishes (_Comátula_), which in its early days is like -a plant with a stalk, but afterwards breaks loose and becomes the -wandering sea-star which we all know so well. In this process there -is just the reverse of that which characterises the barnacles and -sponges, where the young are at first free and then become fixed for -the remainder of their lives. Fig. 30 is the young of another kind of -star-fish, the long-armed Ophiúris, or snake-star. - -Fig. 37 is a portion of the skin of the common sun-star (_Solaster_), -showing the single large spine surrounded by a circle of smaller -spines, supposed to be organs of touch, together with two or three -of the curious appendages called pedicellariæ. These are found on -star-fishes and Echini, and bear a close resemblance in many respects -to the bird-head appendages of the zoophytes. They are fixed on -foot-stalks, some very long and others very short, and have jaws which -open and shut regularly. Their use is doubtful, unless it be to act as -police, and by their continual movements to prevent the spores of algæ, -or the young of various marine animals, from effecting a lodgment on -the skin. A group, of pedicellariæ from a star-fish is shown on a large -scale on Plate XII. Fig. 6, and Fig. 9 of the same Plate shows the -pedicellariæ of the Echinus. - -Upon the exterior of the Echini, or sea-urchins, are a vast number of -spines having a very beautiful structure, as may be seen by Fig. 35, -Plate IX., which is part of a transverse section of one of these -spines. An entire spine is shown on Plate XII. Fig. 12, and shows the -ball-and-socket joint on which it moves, and the membranous muscle that -moves it. Fig. 8 is the disc of the snake-star as seen from below. -Fig. 1 is a portion of skin of the sun-star, to show one of the curious -madrepore-like tubercles which are found upon this common star-fish. -Fig. 3 is a portion of cuttle “bone,” very slightly magnified, in order -to show the beautiful pillar-like form of its structure; and Fig. 4 -is the same object seen from above. When ground very thin this is a -magnificent object for the polariscope. - -One or two miscellaneous objects now come before our notice. Fig. 11 -is one of those curious marine plants, the Corallines, which are -remarkable for depositing a large amount of chalky matter among their -tissues, so as to leave a complete cast in white chalk when the -coloured living portion of the plant dies. The species of this example -is _Jania rubens_. - -Fig. 19 is part of the pouch-like inflation of the skin, and the hairs -found upon the rat’s tail, which is a curious object as bearing so -close a similitude to Fig. 22, the sea-mat zoophyte. Fig. 23 is a -portion of the skin taken from the finger, which has been injected -with a coloured preparation in order to show the manner in which the -minute blood-vessels or “capillaries” are distributed; and Fig. 26 is a -portion of a frog’s lung, also injected. - -The process of injection is a rather difficult one, and requires -considerable anatomical knowledge. The principle is simple enough, -being merely to fill the blood-vessels with a coloured substance, so as -to exhibit their form as they appear while distended with blood during -the life of the animal. It sometimes happens that when an animal is -killed suddenly without effusion of blood, as is often seen in the case -of a mouse caught in a spring trap, the minute vessels of the lungs and -other organs become so filled with coagulated blood as to form what is -called a natural injection, ready for the microscope. - -Before leaving the subject I must ask the reader to refer again for a -moment to the frog’s foot on Plate X., and to notice the arrangement -of the dark pigment spots. It is well known that when frogs live in a -clear sandy pond, well exposed to the rays of the sun, their skins are -bright yellow, and that when their residence is in a shady locality, -especially if sheltered by heavy overhanging banks, they are of a deep -blackish-brown colour. Moreover, under the influence of fear they will -often change colour instantaneously. The cause of this curious fact is -explained by the microscope. - -Under the effects of sunlight the pigment granules are gathered -together into small rounded spots, as seen on the left hand of the -figure, leaving the skin of its own bright yellow hue. In the shade the -pigment granules spread themselves so as to cover almost the entire -skin and to produce the dark brown colour. In the intermediate state -they assume the bold stellate form in which they are shown on the right -hand of the round spots. Very remarkable forms of these cells may be -found in the skin of the cuttle-fish. - -Figs. 24 and 25 are two examples of coal, the former being a -longitudinal and the latter a transverse section, given in order to -show its woody character. Fig. 17 is a specimen of gold-dust intermixed -with crystals of quartz sand, brought from Australia; and Fig. 21 is a -small piece of copper-ore. - -Every possessor of a microscope should, as soon as he can afford it, -add to his instrument the beautiful apparatus for polarising light. -The optical explanation of this phenomenon is far too abstruse for -these pages, but the practical application of the apparatus is very -simple. It consists of two prisms, one of which, called the polariser, -is fastened by a catch just below the stage; and the other, called an -analyser, is placed above the eye-piece. In order to aid those bodies -whose polarising powers are but weak, a thin plate of selenite is -generally placed on the stage immediately below the object. The colours -exhibited by this instrument are gorgeous in the extreme, as may be -seen by Plate XI., which affords a most feeble representation of the -glowing tints exhibited by the objects there depicted. The value of the -polariser is very great, as it often enables observers to distinguish, -by means of their different polarising properties, one class of objects -from another. - -If the expense of a polarising apparatus be too great for the means -of the microscopist, he may manufacture a substitute for it by taking -several thin plates of glass, arranging them in a paper tube so that -the light may meet the surface of the lowest one at an angle of about -52°, and placing the bundle above the eye-piece to act as an analyser; -whilst, by using a plate of glass, and so arranging the lamp that the -light falls upon it at the above angle, and is reflected up the tube -of the microscope, he will find on rotating the extemporised analyser -that the phenomena of polarisation are to a great extent reproduced; -whilst by splitting an extremely thin film from the surface of a sheet -of mica, such as is employed for making smoke-screens above glass -globes, he will have a substitute for the selenite by means of which -alone can the gorgeous effects be produced. The extemporised apparatus -will not, of course, give such perfect effects, but this is sometimes -an advantage, and the present writer has used the same means with -considerable success in photographing starch-granules. - - -XIV. - - FIG. - 1. Dero latissima - 2. Slavina serpentina - 3. Pristina longiseta - 4. Lophopus crystallinus - 5. Fredericella sultana - 6. Stylaria proboscidea (head) - 7. Hydatina senta - 8. Synchœta mordax - 9. Asplanchna Brightwellii - 10. Notommata aurita - 11. Triarthra longiseta - 12. Euchlanis triquetra - 13. Brachionus amphiceros - 14. Salpina mucronata - 15. Pterodina patina - 16. Anurœa brevispina - 17. Dinocharis tetractis - 18. Noteus quadricornis - 19. Floscularia ornata - 20. Young Melicerta - 21. Macrobiotus (sp.?) - 22. Cypris fusca - 23. Cyclops quadricornis - -[Illustration: XIV.] - - - - -CHAPTER XI - - Hints on the Preparation of Objects--Preservative Fluids--Mounting - Media--Treatment of Special Objects. - - -The microscopist who relies altogether on the dealer for his permanent -preparations may expend a good deal of money, but the satisfaction -which he derives from his hobby will be very inferior to that -experienced by the worker who endeavours to secure, for exhibition or -for reference, specimens of the objects which he finds most interesting -and instructive to himself. - -It will be our endeavour in the following pages to give a summary of -the elementary principles upon which reliance is to be placed, though -it must be clearly understood that the technique of the subject, -already occupying a vast amount of literature, is extending day by day, -so that it is impossible to deal exhaustively even with one single -section of it. Reference must be made, for further information, to -such publications as the _Journal of the Royal Microscopical Society_, -or that of the Quekett Club, or to the monographs on the various -departments. Davies’ work on the general subject will also be found -useful by the beginner. - -Taking first the question of reagents, we may mention five which leave -the cells of a tissue as nearly as possible in the natural condition, -but fit for permanent preservation. The first of these, in order of -importance and of general applicability, is alcohol, represented for -most purposes by methylated spirit, which contains about 84 per cent. -of absolute alcohol, though, unfortunately for our purpose, there is -a certain quantity of mineral naphtha in it in addition. This last -has the effect of making it go milky upon dilution with water, which -is a considerable disadvantage, though the milkiness disappears to -some extent on standing, and it is rarely worth the while of the -ordinary microscopist to go through the formalities necessary to obtain -permission to purchase unmineralised spirit, which cannot be had in -quantities of less than five gallons (as it is only to be had from the -distillers under an Excise permit), and distillers may not supply less. - -Four parts of methylated spirit with one of water forms the classical -“70 per cent.” alcohol, the most generally useful of all fluids for -hardening and preserving purposes. A considerable quantity of this -fluid should always be available. - -Whatever other fluid may be used to begin with, spirit must almost -always be used to finish the process, and fit the tissue for -section-cutting and staining. - -Of purely preservative, or fixative, fluids, we may mention “formalin,” -a 40 per cent. solution of formic aldehyde, which is rapidly coming to -the front, as indeed it deserves to do. It is but slightly poisonous, -if at all, and leaves in the tissue nothing which requires subsequent -removal before proceeding to harden for section-work, whilst it is an -admirable preservative of cell-form. - -Another admirable but highly poisonous reagent is corrosive sublimate, -in saturated solution, with 2 per cent. of acetic acid. - -A fourth is osmic acid, used in 1 per cent. solution. This is a highly -valuable reagent, but extremely expensive, very poisonous, and giving -off fumes which are most irritating to the eyes. - -The fifth, a very gentle, but in many respects very satisfactory one, -is picric acid in saturated solution. Tissues preserved in this medium -must not be washed out with water, as it enters into very feeble -combination with protoplasm, and the cells swell and disintegrate as -the reagent is dissolved out. - -Of mounting media we may mention glycerine, glycerine jelly (made -by dissolving starch in glycerine with the aid of heat), and Canada -balsam, dissolved in xylol or benzole. The Canada balsam must be dried -hard by evaporation over a water-bath, and dissolved as wanted. Under -no circumstances should raw balsam be used, as it takes years to set -hard, and turns of a deep yellow colour in the process. - -Chloroform is frequently used as a solvent, but it has the disadvantage -of attacking and extracting a large number of the aniline dyes used for -staining structures, an objection from which the mineral solvents are -free. - -We will now proceed to go through the objects already referred to, and -indicate the method of preservation. - -For the study of the cell-structures of plants the portion to be -examined is to be placed in spirit of about 30 per cent. strength, -which is changed after twenty-four hours for 40 per cent., after a -further twenty-four hours for 55 per cent., and finally, as regards -our present purpose, in 70 per cent. spirit, in which it may remain -until required for section-cutting. The effect of this treatment is -to extract the bulk of the water from the tissue, with the minimum of -shrinkage of the cells, the latter being preserved in their natural -relations to surrounding parts. - -In some cases, however, it is desirable to examine and preserve -delicate structures, or parts, or dissections, in a medium which allows -of the retention of the greater part of the natural moisture, and in -such a case the tissue is immersed in glycerine diluted very much in -the same way as the alcohol in the last process, but with very much -longer intervals between the alterations of strength, until it reaches -pure glycerine, in which it remains for a considerable time, as the -exchange between the tissue and the dense fluid surrounding it goes on -very slowly. - -A combination of the two methods is also possible, the spirit-hardening -being carried out for a portion of the time, and the tissue being -thereafter transferred to glycerine, diluted or pure. - -The object of using glycerine at all is merely that it has a much -lower refractive index than balsam, so that delicate structures may -sometimes be better seen in the former medium, but balsam is to be -preferred wherever it is possible to use it, _i.e._ almost always. -The writer has not mounted a preparation in glycerine or a medium -containing it for many years, nor, with proper staining, does he think -it can ever be necessary to do so, except in the case of dissections -in which the glycerine can be slowly run in without disturbing the -arrangement, as spirit would be pretty sure to do. The harder portions -of plants, woody stems, shells of fruit, or the like, require different -treatment, and must, as a rule, be allowed to dry thoroughly before -being cut. - -Starch granules are somewhat troublesome to mount satisfactorily. -The writer has tried many methods, and, on the whole, prefers a -glycerin-gelatin medium, which keeps for an almost indefinite time, and -may be made as follows: Thirty grains of gelatine (Nelson’s “brilliant” -or other transparent gelatine is to be preferred) are allowed to soak -in water, and the swollen gelatine is drained, and dissolved in the -water which it has absorbed, by the aid of a gentle heat. An equal -bulk of pure glycerine is then added. In using, a small portion is -transferred to a slide with the point of a knife and melted, a small -quantity of starch granules added, and stirred into it with a needle. -The cover-glass is then laid up on the still-fluid drop, pressed gently -down so that the drop is extended to the margin of the cover, and the -whole allowed to cool. It is then to be painted round with several -layers of Brunswick black, or Hollis’s glue, or zinc-white cement, to -prevent evaporation,--Hollis’s glue being perhaps the best medium for -the purpose. - -Petals, or other parts of which it is desired to obtain a surface view, -must be mounted in cells, which may be made by the use of button-moulds -of suitable size, cemented to the glass slide with marine glue. The -slide must be free from grease, as the tissue must be fixed in position -by the use of gum, and allowed to dry thoroughly before closing the -cell, or the cover-glass will be bedewed with moisture when the cell -is closed. The best plan is, after air-drying for a couple of days, -to place the preparation on a metal plate over a beaker of boiling -water for an hour or more, and then to close the cell immediately with -Brunswick black, maintaining the heat at first to ensure rapid drying, -and then slowly withdrawing it. When cool, another coat should be -given, and rather thick covers should be used, as these preparations -are never required to be examined with high powers. - -To mount pollen-grains, they should be sprinkled upon the surface of a -slide which has been previously moistened with thin gum, and allowed -to dry until it has become just “tacky”; the drying is then completed -by gentle heat and a drop of balsam placed upon the grains, with a -cover-glass over all. Bubbles will probably form, but with Canada -balsam this is not of the slightest importance, as they always come -out of their own accord, and balsam mounts should never be closed with -cement of any kind until thoroughly dry. - -Air-bubbles in other media may be eliminated by the use of the -air-pump shown in Fig. 16, which may be obtained from Baker at a very -reasonable rate, and which is useful not only for that purpose, but for -accelerating the drying of moist tissues. To do this, there is placed -upon the plate of the pump a porcelain dish containing strong sulphuric -acid, and upon this is placed a little triangle of platinum wire, which -serves to support the preparation. The air is now exhausted; the tissue -parts with moisture to supply its place, and this moisture is in turn -greedily absorbed by the sulphuric acid, so that drying is rapid and -continuous, as well as very thorough, whilst the process has the great -advantage of dispensing entirely with the use of heat. - -[Illustration: Fig. 16.] - -Portions of many of the delicate algæ may be mounted in glycerine, -having previously been soaked in it as already described; whilst the -unicellular forms, such as desmids and diatoms, may be preserved in -almost exactly the natural condition by simply mounting them in a -saturated solution of picric acid. - -Probably formalin, in a solution of 10 per cent. strength, would answer -the purpose equally well, but the writer has not tried it. It is -hardly necessary to say that, with such extremely fluid media, great -care is required in closing the cell. A thin layer of Hollis’s glue -should be first painted on, to secure the cover in position, and when -this is thoroughly dry, several successive layers must be added in the -same way. - -It may be said here, that it is advisable in all cases to use circular -cover-glasses, as far as possible, as they lend themselves with great -facility to a mechanically accurate closure. This slide is placed -upon a turn-table, carefully adjusted until the cover is seen to be -central when rotated, and a brush, preferably a small camel-hair -pencil, charged with the desired fluid, but not in large excess, is -held against the junction of the slide and cover, whilst the table -is rapidly spun. A little experience will teach better than any -description what amount of fluid there should be in the brush, and how -thick the cement should be. If too thick, it will drag off the cover; -if too thin, it will flow over the latter and over the slide. - -The preparation of diatom-skeletons as permanent objects is easy. -Consisting, as they do, of pure silex, or flint,--_i.e._, practically -glass,--they resist long boiling in acids, so that there is little -difficulty in isolating them from any organic matter with which they -are mingled. It is generally recommended to treat them with strong -nitric acid. This is a mistake. The acid acts much more powerfully -and less violently when diluted with an equal bulk of water, and it -is in an acid so diluted that portions of water-plants, or other -diatomaceous material, should be boiled in a glass beaker until all the -organic matter is dissolved. The beaker should be covered with a glass -plate, to prevent dissipation of the acid fumes. When the process is -complete, usually in about half an hour, the contents of the beaker are -thoroughly stirred with a glass rod, poured rapidly off into a larger -bulk of cold water, and allowed to settle for another half-hour. The -process is then repeated with a smaller bulk of water, several times, -to allow the removal of the last traces of acid, and finally with -distilled water. The separation of the diatoms into grades is effected -by settlement. The final result is poured into a tall glass vessel, -and allowed to settle for, at first, a minute, the supernatant fluid -again poured off, and allowed to settle for two minutes, and so on, the -period being gradually increased, and each sediment preserved apart. -The first will probably only be sand, but the proportion of diatoms -will increase with each separation, though there will always be a -certain proportion of sand of such a size as to settle at the same rate -as the diatoms. Marine plants especially will furnish a rich harvest by -treatment as described. - -Solid diatomaceous deposits, such as kiesel-guhr, mountain-meal, and -especially the famous Oamaru deposit from New Zealand, demand different -treatment, and perhaps the best way is to disintegrate the mass, either -by boiling with Sunlight soap (though the alkali attacks the flint to -some extent) or to mix the mass with a super-saturated solution of -acetate of soda (made by saturating water with the crystals whilst -boiling), and by successive coolings, heatings, and stirrings to cause -the process of crystallisation to break up the mass, which it will do -very thoroughly. The diatoms are then separated by sedimentation, as -above described. - -A small portion of the deposit may now be spread thinly on a glass -slide, allowed to dry thoroughly, be treated with balsam, and covered. - -If it be desired to select individual diatoms, this must be done under -the microscope, by means of a bristle fixed in a handle either with -glue or sealing-wax. The diatom selected will adhere to the bristle -if the latter be slightly greasy, and should then be transferred to -a slightly adhesive slide, coated either with thin solution of white -shellac, or with thin gum nearly dry. When the forms desired are -mounted, the preparation should be covered in balsam. The process is by -no means as easily effected as described, however. - -The preparation of insects, or parts of insects, as microscopic objects -is a tedious and difficult task. The main point is the trouble of -softening the integument and eliminating the colour. - -The latter can, in any case, be only partially effected. The beginner -would do well to begin with a fairly easy form, such as the worker-ant. -A good supply of these insects may be placed in a bottle of liquor -potassæ, and left there for at least some days until they begin to -become clear and limp. From time to time a specimen may be taken, -well washed with several waters, then with acetic acid and water of -a strength of about 10 per cent., then with weak spirit, about 50 per -cent. An attempt may then be made to arrange the insect upon a slide, -spreading out the legs so as to exhibit them to the best advantage, and -when this has been done a cover-glass may be put on, supported in such -a way as to prevent absolute pressure. The spirit is then withdrawn -by means of a piece of filtering-paper cut to a point, and strong -spirit added. This is again succeeded by absolute alcohol, then by a -mixture of turpentine and crystal carbolic acid in equal proportions, -and finally the cover-glass is carefully lifted, and some thick balsam -solution dropped on, the limbs finally arranged by means of warm -needles, and the cover-glass carefully replaced and pressed gently down -by means of a clip, which may be obtained for a few pence. The whole -is then set aside to harden, the deficiency caused by evaporation made -good, the balsam allowed to dry, and the preparation finally painted -round. - -The contents of the body, in large insects, must be removed, and this -is effected during the washing in water by gentle pressure with a -camel-hair brush, the process being aided, if necessary, by a small -incision made through the integument at the root of the tail. Sections -of insects require very special methods, which will hardly fall within -the scope of this work. - - - - -CHAPTER XII - -Section-Cutting--Staining - - -No method of examination can equal, for general applicability and -usefulness, that of section-work. The relations of the parts to each -other being preserved, it is possible to draw conclusions as to their -actual relations which no other mode allows of, and we shall devote -this concluding chapter to some account of the methods to be employed -to this end. - -The apparatus required is not necessarily complicated. Reduced to its -elements, it consists essentially only of a razor to cut the sections -and a dish to receive them. It but seldom happens, however, that the -relations of the parts in sufficiently thin sections can be preserved -by such a rough-and-ready method, and frequently the object to be cut -is of such small dimensions as to render it impossible to deal with it -in this way. It is therefore necessary to “imbed” it, so as to obtain -a handle by which to hold it, in such a way that it shall be equally -supported in all directions. Moreover, since the human hand can only -in exceptional cases be brought to such a pitch of skill as to cut a -series of sections, or even single ones, of the needful delicacy, some -mechanical means of raising the object through a definite distance is -highly desirable. The writer has cut many thousands of sections with -the “free hand,” but the personal equation is a large one, and is not -always the same in the same person. For single sections the method -will, with practice, succeed very well, but some means of securing -a number of sections of more or less the same thickness is usually -required. - -Let us deal with the imbedding first. - -If it be desired to imbed a tissue which has merely been fixed -with formalin, the block should be immersed in strong gum (made by -saturating water with picked gum arabic, white and clean) for several -days. It is then taken out and, without draining, transferred to the -plate of a freezing microtome, and the sections cut from the frozen -block, and mounted in glycerine at once. - -This plan is of limited usefulness, since it allows of very little -differentiation of the tissue elements, and that only optical. - -To get the best results, some plan of staining must be adopted. Perhaps -the simplest, and certainly a very excellent one, is as follows. After -the tissue has been passed from the hardening, or fixing, fluid into -the successive alcohols, as described, it is placed in the following -solution. Take about forty grains of carmine and eighty grains of -borax, dissolve in about an ounce of water, add to the mixture an ounce -of methylated spirit, and let it stand for some time with frequent -shaking; about a week will be sufficient, and the process of solution -may be hastened by gentle warming at intervals. The clear upper portion -is then poured off, and into this the block of tissue is dropped, and -allowed to remain until thoroughly penetrated. Perhaps the best plan is -to substitute the carmine solution for the 50 per cent. alcohol, and -thus to make the staining a stage in the hardening process. From the -carmine solution the tissue is transferred to 70 per cent. alcohol, to -each ounce of which two drops of hydrochloric acid have been added, and -after remaining in it for a day (with a piece of the usual size) is -placed in 70 per cent. alcohol, in two successive quantities. Sections -from this material now only require treatment with the carbolic acid -and turpentine above mentioned to be fit for mounting and covering in -balsam. We now proceed to indicate how the sections may be cut. - -A mixture of wax and almond oil, in proportions varying with the -heat of the weather, usually about equal ones, is prepared. The -piece of tissue is freed from superfluous spirit by being placed on -a bit of blotting-paper for a minute or two, and is then immersed in -a quantity of the wax-and-oil mixture contained in a little box of -paper or lead-foil. The tissue is held on the point of a needle, and -lifted up and down until it is coated with the mixture, and, before -solidification of the mass sets in, is lowered into the box and left -to cool. The block now furnishes a handle, and this should be wrapped -round with paper, the sections cut with the keenest possible razor, -and as thin as possible, and placed in spirit as cut. From the spirit, -which must be the strongest obtainable, they are placed in the clearing -liquid, carbolic and turpentine, and then slid on to the slide, a drop -of balsam placed on the section, and the cover over all. Of late years -all sections of ordinary soft tissues, animal or vegetable, have been -cut by one of the infiltration methods, in which the interstices of the -tissue are filled up by some material which prevents the relations of -the cells from being altered during the process of cutting. To enter -fully into this matter would occupy too much space, and would serve no -useful purpose, for the worker who requires to make use of such means -will find it indispensable to obtain Bolles Lee’s _Microtomist’s Vade -Mecum_, in which the whole matter is exhaustively treated. - -The simple method above detailed will answer most ordinary purposes, -provided that a few precautions be attended to. The chief are as -follows. The outside of the block of tissue must be sufficiently dry -for the wax-and-oil to adhere to it. The razor must be extremely -sharp, and must be kept so by application to a Turkey stone during -the section-cutting. The blade must be drawn across the tissue from -heel to point, and kept wetted with spirit the whole time, so as to -prevent any dragging of the section. The transference of the section to -the slide must be effected by means of a section-lifter, which may be -made by beating out a piece of stout copper wire to a thin flat blade; -or a small palette-knife, or German-silver lifter, may be purchased -for a few pence. The carbolic turpentine is best used by placing a -little in a watch-glass, and floating the sections on to it by lifting -them singly with the lifter, freeing them from superfluous spirit -by draining on to blotting-paper, and allowing them to float on to -the surface of the liquid in the watch-glass, so that the spirit may -evaporate from above, and be replaced by the clearing agent from below -The balsam solution should be thin, and the cover-glass must be allowed -to settle down into place without pressure. - -The question of staining sections is a very large one, and is becoming -of daily increasing complexity. - -We cannot go into it here, further than to say that most sections cut -from unstained tissue will yield excellent results if stained first -with Delafield’s logwood solution (to be obtained at Baker’s) to a -very slight extent, and then with a solution of safranin. The sections -should be washed with tap-water after the logwood stain, and should be -of a pale violet colour. If over-stained, the colour may to a great -extent be removed by washing with a very weak solution of hydrochloric -acid, about two drops of acid to each ounce of water, and repeated -washing in tap-water to remove the acid, and restore the violet. The -safranin stain should be weak, and should be allowed to act for some -time. From this last the sections are transferred to strong spirit, -the latter being renewed until the sections cease to give up the red -dye; and they may then be mounted as described. The results with most -tissues are superb, every detail of the structure being splendidly -brought out. Safranin alone is also an admirable stain for many -purposes. - -Further information must be sought in the book already mentioned. -Let us, in closing, warn the beginner of two things which are of -general application in practical microscopy. The first is, not to be -discouraged by failures. The manipulations are in many cases very -delicate, and premiums must be paid to experience for insurance against -failure in every one of the processes. - -The second is, that the most scrupulous cleanliness will hardly suffice -to prevent contamination of preparation by the all-pervasive dust -which, invisible to the eye, assumes colossal proportions under the -microscope, and the particles of which have an unpleasant habit of -collecting on the most interesting or most beautiful portion of the -preparation. This can only be guarded against by careful filtration of -all fluids, and constant watchfulness. - -A preparation properly made is a thing of beauty, and a joy for -ever,--or if not for ever, at any rate for many years; and one such -will repay an infinitude of pains taken in its production. - - - - -INDEX - - - PAGE - Air-pump, 174 - Algæ, 78 - " marine, 92 - Anemones, sea, 159 - Antennæ, 96 - Ants, 97 - - Bacillaria, 87 - Balancers of Fly, 112 - Bark, 61 - Blights, 89 - Blood, circulation of, 129 - " corpuscles of, 128 - Bone, 123 - Breathing-tubes, 109 - Bull’s-eye, use of, 32 - - Camera lucida, 25 - Canada Balsam, 170 - Cartilage, 124 - Cells, animal, 122 - " circulation in, 40 - " mounting dry in, 173 - " pigment, 121, 165 - " spiral, 46 - " vegetable, 37 - Ceramidia, 93 - Chlorophyll, 40 - Compressorium, Beck’s, 18 - Condenser, bull’s-eye, 19 - " substage, 19 - Confervæ, 84 - Conjugation, 82, 84 - Convex lenses, 7 - " foci of, 7, 8 - " image formed by, 10 - " virtual image, 11 - Corallines, 164 - Corrosive sublimate, 170 - Cover-glasses, 18 - - Desmids, 81 - Diatoms, 85 - " preparation of, 175 - Dipping-tubes, 22 - Dissection, 20 - " instruments, 21 - " under microscope, 24 - Drawing, 25 - " squares, 26 - - Echinoderms, 162 - Entomostraca, 152 - Epidermis, animal, 122 - " vegetable, 68 - Extemporised apparatus, 5 - - Feathers, 119 - Fish, scales of, 118 - " parasites of, 153 - Fixation of cell-forms, 171 - Focus of mirror, 29 - Foraminifera, 156 - Formalin, 164 - Frog-plate, 129 - - Gills of mussel, 122 - Gizzard of insects, 109 - Glycerine-gelatine, 172 - " jelly, 171 - - Hairs, animal, 116 - " vegetable, 53 - Heads of Insects, 104 - - Illumination, correct, 31, 32 - " dark-field, 34 - " for opaque objects, 33 - Imbedding, 180 - " by infiltration, 182 - Infusoria, 135 - Injection, 164 - Insects, 97 - " mounting of, 177 - - Jelly-fish, 158 - - Larva of _Chironomus_, 152 - Light, arrangement of, 29 - Live-box, 17 - Logwood solution, 183 - - Magnification, to measure, 27 - Mare’s tail, 91 - Marine life, 155 - Microscope, Baker’s, 14 - " " “portable”, 15 - " primitive, 5 - " simple, 12, 13 - Mildew, 89 - Mirror, concave, 29 - Mollusca, 161 - Mounting, 168 - " dry, 173 - " foraminifera, 157 - Mosses, 96 - Muscle, 127 - - Nails, 124 - Needles, 22 - Nerve, 127 - Net, 133 - Nucleus, 40 - - Objectives, 16 - Objects, drawing of, 24 - " photography of, 36 - Oil-cells, 58, 61 - Oscillatoriæ, 84 - Osmic acid, 170 - - Parasites, 153 - Petals, 69 - Picric acid, 170 - Pigment, 121 - Pocket magnifiers, 13 - Polariscope, 166 - Pollen, 71 - Polyzoa, 147 - Pond-hunting, 132 - Preservatives, 169 - - Radiolaria, 157 - Rotifers, 147 - - Safranin stain, 183 - Sap, 128 - Scent-glands, 57 - Sea-weeds, 92 - Section-cutting, 178 - Seeds, 75 - Skin, 120 - Spiracles, 102 - Sponge, fresh-water, 135 - " spicules, 155 - Sporangia, 92 - Stage-forceps, 116 - Starch, 63 - " mounting, 172 - Stomata, 49 - Suckers, 108 - - Teeth, 125 - Troughs, glass, 18 - - Water-bears, 152 - Wings, 110 - Wool, 116 - Worms, fresh-water, 14 - " marine, 160 - - Yeast, 89 - - Zoœa, 161 - Zoophytes, 157 - Zygnemaceæ, 85 - - -PRINTED BY MORRISON AND GIBB LIMITED, EDINBURGH - - - - - -End of Project Gutenberg's Common Objects of the Microscope, by J. 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G. Wood - -This eBook is for the use of anyone anywhere in the United States and most -other parts of the world at no cost and with almost no restrictions -whatsoever. You may copy it, give it away or re-use it under the terms of -the Project Gutenberg License included with this eBook or online at -www.gutenberg.org. If you are not located in the United States, you'll have -to check the laws of the country where you are located before using this ebook. - - - -Title: Common Objects of the Microscope - -Author: J. G. Wood - -Editor: E. C. Bousfield - -Illustrator: Tuffen West - -Release Date: July 18, 2017 [EBook #55146] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK COMMON OBJECTS OF THE MICROSCOPE *** - - - - -Produced by Thiers Halliwell, Chris Curnow and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive) - - - - - - -</pre> - - -<div class="transnote"> - -<p><b>Transcriber’s notes</b>:</p> - -<p>Minor punctuation errors have been corrected silently (e.g. missing -full stops after abbreviated words such as Fig), as have the following -misspellings: Bretahing → Breathing, Pedicillaria → Pedicellaria, -Pedicelaria → Pedicellaria, Chœtonotus → Chætonotus, Spurganium -→ Sparganium, veiw → view. Unorthodox spelling and inconsistent -hyphenation has not been altered. Several wrongly numbered -cross-references to Plates and Figures have been corrected.</p> - -<p>Plate VIII (and its accompanying key) was originally displayed -at the beginning of the book, before the Title Page, but has been -repositioned in the body of the text in correct numerical sequence.</p> - -<p>A black underline indicates a hyperlink to a page or illustration -(hyperlinks are also highlighted when the mouse pointer hovers over -them).<span class="htmlonly"> Page numbers are shown in the right -margin.</span></p> - -<p class="epubonly">The cover image of the book was created by the -transcriber and is placed in the public domain.</p> -</div> - - -<div class="figcenter" style="width: 563px;"> - <img id="coverpage" src="images/cover.jpg" width="563" height="700" alt="Book cover" /> -</div> - - -<div class="titlepage"> - -<h1>COMMON OBJECTS OF<br /> -THE MICROSCOPE</h1> - - -<div class="tp1">BY THE LATE</div> - -<div class="tp2"><span class="smcap">Rev.</span> J. G. WOOD, M.A., F.L.S., <span class="smcap">Etc.</span></div> - -<div class="tp3">AUTHOR OF<br /> -“COMMON OBJECTS OF THE COUNTRY” “COMMON OBJECTS OF THE SEA-SHORE”<br /> -“MY FEATHERED FRIENDS” ETC. ETC.</div> - - -<div class="tp1 mtb4em">WITH ILLUSTRATIONS BY TUFFEN WEST</div> - - -<div class="tp1"><i>SECOND EDITION, REVISED AND RE-WRITTEN, BY</i></div> - -<div class="tp4">E. C. BOUSFIELD, L.R.C.P.(<span class="smcap">Lond.</span>)</div> - -<div class="tp3">AUTHOR OF<br /> -“A GUIDE TO THE SCIENCE OF PHOTO-MICROGRAPHY”</div> - -<div class="tp1 mtb4em">WITH ADDITIONAL ILLUSTRATIONS BY THE REVISER</div> - - -<div class="tp4">LONDON<br /> -GEORGE ROUTLEDGE AND SONS, <span class="smcap">Limited</span></div> - -<div class="tp1">BROADWAY HOUSE, LUDGATE HILL</div> - -<div class="tp4">1900</div> -</div> - - - -<hr class="chap" /> -<p><span class="pagenum" title="v"><a name="Page_v" id="Page_v"></a></span></p> - -<h2>PREFACE TO THE SECOND EDITION</h2> - - -<p>The task of revising and bringing up to date a work -which has been the guide, philosopher, and friend -of thousands of commencing microscopists has been, -in the present case, one of no small difficulty. -On the one hand, there was the natural desire to -interfere as little as possible with the original work; -and on the other, the necessity of rendering available, -to some extent at least, the enormous advance -in every department which has taken place in the -thirty-six years which have elapsed since the work -was first offered to the public. The reviser has -done his best not only to fulfil these two objects, -but to keep in view the original purpose of the -book.</p> - -<p>In the popular department of pond-life especially, -about fifty new illustrations have been added, mostly -from the reviser’s own notebook sketches. The -whole of the botanical part has been revised by one<span class="pagenum" title="vi"><a name="Page_vi" id="Page_vi"></a></span> -of our first English authorities, and, in short, no -effort has been spared to make the work as accurate -as its necessarily condensed form permits of. It is -hoped, therefore, that it may be found not less -useful than its predecessor by those for whom it is -alone intended.</p> - -<hr class="chap" /> - -<div class="chapter"> -<p><span class="pagenum" title="vii"><a name="Page_vii" id="Page_vii"></a></span></p> - - - - -<h2>PREFACE TO THE FIRST EDITION</h2> -</div> - - -<p>In my two previous handbooks, the “Common -Objects” of the Sea-shore and Country, I could -but slightly glance at the minute beings which -swarm in every locality, or at the wonderful -structures which are discovered by the Microscope -within or upon the creatures therein described. -Since that time a general demand has arisen for -an elementary handbook upon the Microscope and -its practical appliance to the study of nature, and -in order to supply that want this little volume has -been produced.</p> - -<p>I must warn the reader that he is not to expect -a work that will figure and describe every object -which may be found on the sea-shore or in the -fields, but merely one by which he will be enabled -to guide himself in microscopical research, and -avoid the loss of time and patience which is almost -invariably the lot of the novice in these interesting -studies. Upwards of four hundred objects have -been figured, including many representatives of -the animal, vegetable, and, mineral kingdoms, and<span class="pagenum" title="viii"><a name="Page_viii" id="Page_viii"></a></span> -among them the reader will find types sufficient for -his early guidance.</p> - -<p>Neither must he expect that any drawings can -fully render the lovely structures which are revealed -by the microscope. Their form can be given faithfully -enough, and their colour can be indicated; -but no pen, pencil, or brush, however skilfully -wielded, can reproduce the soft, glowing radiance, -the delicate pearly translucency, or the flashing -effulgence of living and ever-changing light with -which God wills to imbue even the smallest of His -creatures, whose very existence has been hidden for -countless ages from the inquisitive research of man, -and whose wondrous beauty astonishes and delights -the eye, and fills the heart with awe and adoration.</p> - -<p>Owing to the many claims on my time, I left the -selection of the objects to Mr. Tuffen West, who -employed the greater part of a year in collecting -specimens for the express purpose, and whose well-known -fidelity and wide experience are the best -guarantees that can be offered to the public. To -him I also owe many thanks for his kind revision -of the proof-sheets. My thanks are also due to -Messrs. G. and H. Brady, who lent many beautiful -objects, and to Messrs. Baker, the well-known -opticians of Holborn, who liberally placed their -whole stock of slides and instruments at my disposal.</p> - -<hr class="chap" /> - -<div class="chapter"> -<p><span class="pagenum" title="ix"><a name="Page_ix" id="Page_ix"></a></span></p> - - -<h2>CONTENTS</h2> -</div> - -<hr class="r5" /> - -<div class="center"> -<table class="toc" border="0" cellpadding="0" cellspacing="0" summary="table of contents"> -<tr><td class="tac fs110 pt1" colspan="2"><div>CHAPTER I</div></td></tr> -<tr><td></td><td class="tar vab fs80 lh05em">PAGE</td></tr> -<tr><td class="tal pr1 plhi22">Pleasures and Uses of Microscopy—Development of the -Microscope—Extemporised Apparatus</td><td class="tar vab"><div><a href="#Page_1">1</a></div></td></tr> - -<tr><td class="tac fs110 pt1" colspan="2"><div>CHAPTER II</div></td></tr> -<tr><td class="tal pr1 plhi22">Elementary Principles of Optics—Simple Microscopes—Compound -Microscope—Accessory Apparatus—Cover-glasses—Troughs— -Condensers—Dissection—Dipping-tubes—Drawing—Measurement</td><td class="tar vab"><div><a href="#Page_7">7</a></div></td></tr> - -<tr><td class="tac fs110 pt1" colspan="2"><div>CHAPTER III</div></td></tr> -<tr><td class="tal pr1 plhi22">Examination of Objects—Principles of Illumination—Mirror -and its Action—Substage Condenser—Use of Bull’s-eye—Opaque -Objects—Photography of Microscopic Objects</td><td class="tar vab"><div><a href="#Page_28">28</a></div></td></tr> - -<tr><td class="tac fs110 pt1" colspan="2"><div>CHAPTER IV</div></td></tr> -<tr><td class="tal pr1 plhi22">Vegetable Cells and their Structure—Stellate Tissues—Secondary -Deposit—Ducts and Vessels—Wood-Cells—Stomata, -or Mouths of Plants—The Camera Lucida, and -Mode of Using—Spiral and Ringed Vessels—Hairs of -Plants—Resins, Scents, and Oils—Bark Cells</td><td class="tar vab"><div><a href="#Page_37">37</a></div></td></tr> - -<tr><td class="tac fs110 pt1" colspan="2"><div>CHAPTER V</div></td></tr> -<tr><td class="tal pr1 plhi22">Starch, its Growth and Properties—Surface Cells of Petals—Pollen -and its Functions—Seeds</td><td class="tar vab"><div><a href="#Page_63">63</a></div><span class="pagenum" title="x"><a name="Page_x" id="Page_x"></a></span></td></tr> - -<tr><td class="tac fs110 pt1" colspan="2"><div>CHAPTER VI</div></td></tr> -<tr><td class="tal pr1 plhi22">Algæ and their Growth—Desmidiaceæ, where found—Diatoms, -their Flinty Deposit—Volvox—Mould, Blight, -and Mildew—Mosses and Ferns—Mare’s-Tail and the -Spores—Common Sea-weeds and their Growth</td><td class="tar vab"><div><a href="#Page_78">78</a></div></td></tr> - -<tr><td class="tac fs110 pt1" colspan="2"><div>CHAPTER VII</div></td></tr> -<tr><td class="tal pr1 plhi22">Antennæ, their Structure and Use—Eyes, Compound and -Simple—Breathing Organs—Jaws and their Appendages—Legs, -Feet, and Suckers—Digestive Organs—Wings, -Scales, and Hairs—Eggs of Insects—Hair, Wool, Linen, -Silk, and Cotton—Scales of Fish—Feathers—Skin and -its Structure—Epithelium—Nails, Bone, and Teeth—Blood -Corpuscles and Circulation—Elastic Tissues—Muscle -and Nerve</td><td class="tar vab"><div><a href="#Page_96">96</a></div></td></tr> - -<tr><td class="tac fs110 pt1" colspan="2"><div>CHAPTER VIII</div></td></tr> -<tr><td class="tal pr1 plhi22">Pond-Life—Apparatus and Instructions for Collecting Objects—Methods -of Examination—Sponge—Infusoria</td><td class="tar vab"><div><a href="#Page_132">132</a></div></td></tr> - -<tr><td class="tac fs110 pt1" colspan="2"><div>CHAPTER IX</div></td></tr> -<tr><td class="tal pr1 plhi22">Fresh-water Worms—Planarians—Hydra—Polyzoa—Rotifers -Chætonotus—Water-Bears</td><td class="tar vab"><div><a href="#Page_144">144</a></div></td></tr> - -<tr><td class="tac fs110 pt1" colspan="2"><div>CHAPTER X</div></td></tr> -<tr><td class="tal pr1 plhi22">Marine Life—Sponges—Infusoria—Foraminifera—Radiolaria—Hydroid -Zoophytes—Polyzoa—Worms—Lingual Ribbons and Gills of Mollusca— -Star-Fishes and Sea-Urchins—Cuttle-Fish—Corallines—Miscellaneous -Objects</td><td class="tar vab"><div><a href="#Page_154">154</a></div></td></tr> - -<tr><td class="tac fs110 pt1" colspan="2"><div>CHAPTER XI</div></td></tr> -<tr><td class="tal pr1 plhi22">Hints on the Preparation of Objects—Preservative Fluids—Mounting -Media—Treatment of Special Objects</td><td class="tar vab"><div><a href="#Page_168">168</a></div></td></tr> - -<tr><td class="tac fs110 pt1" colspan="2"><div>CHAPTER XII</div></td></tr> -<tr><td class="tal pr1 plhi22">Section-Cutting—Staining</td><td class="tar vab"><div><a href="#Page_179">179</a></div></td></tr> -</table></div> - -<hr class="chap" /> - -<div class="chapter"> -<p><span class="pagenum" title="1"><a name="Page_1" id="Page_1"></a></span></p> - -<p class="fs200 tac">COMMON OBJECTS OF THE<br />MICROSCOPE</p> - - -<hr class="r5" /> -<h2>CHAPTER I</h2> -</div> - -<p class="subhead">Pleasures and Uses of Microscopy—Development of the -Microscope—Extemporised Apparatus.</p> - - -<p>Within the last half-century the use of the -microscope, not only as an instrument of scientific -research, a tool in the hands of the investigator -of the finer organisation of the world of nature, -nor even as an adjunct to the apparatus of the -chemist or the manufacturer, but as a means of -innocent and instructive recreation, has become -so firmly rooted amongst us that it seems hardly -necessary to advocate its claims to attention on -any of these grounds.</p> - -<p>So wonderful is the information which it affords, -so indispensable is it in many, if not in all, -branches of scientific research, that not only would -the lover of nature be deprived of one of his most -valued sources of information and enjoyment, but<span class="pagenum" title="2"><a name="Page_2" id="Page_2"></a></span> -some sciences would be brought absolutely to a -standstill if by any conceivable means the -microscope were to be withdrawn from their -followers.</p> - -<p>On the other hand, from every improvement in -the construction of the latter, a corresponding enlargement -and enlightenment of the fields reviewed -by these sciences has taken place, and the beauty -and interest of the revelations made by its means -has attracted an ever-increasing host of earnest -and intelligent volunteers, who have rendered -yeoman service to the cause of knowledge.</p> - -<p>Moreover, so vast is the scope of the instrument, -that whilst discoveries in other fields of research -are few and far between, comparatively speaking, -in microscopic science they are of everyday -occurrence, and the number of problems calling -for solution by means of the instrument in question -is so vast that even the humblest worker may be -of the greatest assistance.</p> - -<p>In the following pages we propose to carry out, -as far as possible with reference to the microscope, -the system followed in the “Common Objects of -the Seashore and of the Country,” and to treat in -as simple a manner as may be of the marvellous -structures which are found so profusely in our -fields, woods, streams, shores, and gardens. Moreover, -our observations will be restricted to an -instrument of such a class as to be inexpensively -purchased and easily handled, and to those pieces -of supplementary apparatus which can be extemporised -at small cost of money and ingenuity by<span class="pagenum" title="3"><a name="Page_3" id="Page_3"></a></span> -the observer himself, or obtained of the opticians -for a few shillings.</p> - -<p>With the same view, the descriptions will be -given in language as simple and as free from -technicalities as possible, though it must be -remembered that for many of the organisms and -structures which we shall have to describe there -are none but scientific names; and since, moreover, -this little work is intended to furnish a stepping-stone -between the very elements of microscopic -science, and those higher developments of it which -should be the aim of every worker, it would be -unwise to attempt to invent commonplace appellations -for the purpose of this book, and leave him -to discover, when he came to consult works of -reference in any particular subject, that his -“simplified” knowledge had all to be unlearnt, -and a new vocabulary acquired. Rather will it be -our purpose to use correct terms, and explain them, -as far as necessary, as we introduce them.</p> - -<p>The commencing microscopist is strongly recommended, -whilst not confining his interest entirely -to one branch of research or observation, to adopt -some one as his particular province.</p> - -<p>The opportunities for discovery and original -work, which are afforded by all alike, will be more -readily appreciated and utilised by adopting such -a plan than by a general and purposeless distribution -of effort. To mention one or two. The -student of the fascinating field of pond-life will find -new organisms awaiting description by the hundred, -and of the old ones, life-histories to make out; if<span class="pagenum" title="4"><a name="Page_4" id="Page_4"></a></span> -he be attracted rather to the vegetable inhabitants -of the same realm, the diatoms will furnish him -with the opportunity of studying, and perhaps -solving, the enigma of their spontaneous movement, -and of watching their development. The smaller -fungi, and indeed the larger ones too, will amply -repay the closest and most laborious study of their -habits of life and processes of development. Since -the first edition of this work was published, the -whole subject has been practically revolutionised, -and more remains to be done than has yet been -accomplished.</p> - -<p>In short, there is scarcely an organism, even of -those best known and most studied, which is so -completely exhausted that persevering investigation -would reveal nothing new concerning it.</p> - -<p>There can be little doubt but that if any worker, -with moderate instrumental means, but with an -observant mind, were to set determinately to work -at the study of the commonest weed or the most -familiar insect, he, or she, would by patient labour -accomplish work which would not only be of value -to science, but would redound to the credit of the -worker.</p> - -<p>Something like finality appears to have been -reached, at least for the present, in the development -of the microscope; and whilst it is beyond -the scope of this work to treat of the refined and -costly apparatus which is essential to useful work -in certain departments of research, the result has, -on the whole, been highly favourable to the worker -of moderate means and ambitions, since lenses are<span class="pagenum" title="5"><a name="Page_5" id="Page_5"></a></span> -now accessible, at the cost of a few shillings, comparatively -speaking, which could not have been -purchased at all when this work first appeared. -It is with such appliances that we have here to -deal. The worker whose finances are restricted -must be contented to extemporise for himself many -pieces of apparatus, and will find pleasure and -occupation in doing so. And let him remember, -for his encouragement, that many such home-made -appliances will fulfil their purpose quite as well as -the imposing paraphernalia of glittering brass and -glass which decorates the table of the wealthy -amateur. It is not the man who possesses the -best or most costly apparatus, but the one who -best understands the use of that which he possesses, -that will make the most successful microscopist. -A good observer will discover, with only the aid of -a pocket-magnifier, secrets of Nature which have -escaped the notice of a whole army of dilettante -microscopists, in spite of the advantages which, as -regards instruments, the latter may enjoy.</p> - -<p>It is for those who desire to be of the former -class that this book is written, and in the course -of the following pages instances will be given in -which the exercise of a small amount of ingenuity -and the expenditure of a few pence will be found -equivalent to the purchase of costly and complicated -apparatus.</p> - -<p>An enormous amount of valuable work was done -in the earliest days of microscopy, when the best -apparatus available was a single lens, composed of -the bead formed by fusing the drawn-out end of a<span class="pagenum" title="6"><a name="Page_6" id="Page_6"></a></span> -rod of glass. Inserted into a plate of metal, or a -piece of card, such a primitive instrument was -capable of affording a large amount of information. -Similar instruments are to be purchased for a few -pence at the present day, and are not without their -use for purposes of immediate examination of -material. A very common form is a glass marble, -ground flat on one side, and mounted in a tube. -The material to be examined is placed upon the -flat side, and is seen magnified to an extent -inversely proportional to the diameter of the sphere -of glass.</p> - -<hr class="chap" /> - -<div class="chapter"> -<p><span class="pagenum" title="7"><a name="Page_7" id="Page_7"></a></span></p> - - - - -<h2>CHAPTER II</h2> -</div> - -<p class="subhead">Elementary Principles of Optics—Simple Microscopes—Compound Microscope—Accessory Apparatus—Cover-glasses—Troughs—Condensers—Dissection—Dipping-tubes—Drawing—Measurement.</p> - - -<p>Before proceeding to deal with the microscope -itself, it may be useful to give a short summary of -the optical laws upon which its working depends.</p> - -<p>To go into the minutiæ of the matter here would -be out of place, but it will be found very helpful, -especially in the matter of illumination, to acquire -some knowledge of, and facility in applying, these -elementary principles. We shall confine our -remarks to convex lenses, as being the form to -which all the combinations in the microscope may -be ultimately reduced.</p> - -<p>Every convex lens has one “principal” focus, -and an infinite number of “conjugate” foci. The -principal focus is the distance at which it brings -together in one point the rays which fall upon it -parallel to its axis, as shown in Fig. <a href="#Fig_1">1</a>, in which <i>A</i> -is the axis of the lens <i>L</i>, and the rays <i>RR</i> are -brought together in the principal focus <i>P</i>. Thus -a ready means of finding the focal length of any -lens is to see at what distance it forms an image<span class="pagenum" title="8"><a name="Page_8" id="Page_8"></a></span> -of the sun, or of any other distant object, upon a -screen, such as a piece of smooth white cardboard. -In the figure this distance will be <i>PL</i>. Conversely, -if the source of light be at <i>P</i>, a parallel beam of -light will be emitted from the lens.</p> - -<div class="figcenter" style="width: 465px;"> -<a id="Fig_1"></a> -<img src="images/i_008.jpg" width="465" height="206" alt="" /> -<div class="caption"><p><span class="smcap">Fig. 1.</span></p></div> -</div> - -<p>The focal length may, however, be found in -another way. When an object is placed at a -distance from a lens equal to twice the principal -focal length of the latter, an image of the object is -formed at the same distance upon the other side of -the lens, inverted in position, but of the same -dimensions as the original object. The object and -image then occupy the equal conjugate foci of the -lens, so that by causing them to assume these -relative positions, and halving the distance at -which either of them is from the lens, the focal -length of the latter is known.</p> - -<p>These points will be seen on reference to Fig. <a href="#Fig_2">2</a>, -in which <i>L</i> being the lens, and <i>P</i> the principal -focus, as before, rays from the point <i>C</i> are brought -together at the conjugate focus <i>C'</i>, at the same<span class="pagenum" title="9"><a name="Page_9" id="Page_9"></a></span> -distance on the other side of <i>L</i>. In this case it -manifestly does not matter whether the object be -at one or the other of these points.</p> - -<div class="figcenter" style="width: 480px;"> -<a id="Fig_2"></a> -<img src="images/i_009.jpg" width="480" height="192" alt="" /> -<div class="caption"><p><span class="smcap">Fig. 2.</span></p></div> -</div> - -<p>So far we have been dealing with points on the -line of the axis of the lens. The facts mentioned -apply equally, however, to rays entering the lens -at an angle to the axis, only that in this case they -diverge or converge, correspondingly, upon the -other side. It is evident, from Fig. <a href="#Fig_1">1</a>, that no -image is formed of a point situated at the distance -of the principal focus; but Fig. <a href="#Fig_3">3</a>, which is really -an extension of Fig. <a href="#Fig_2">2</a>, shows how the rays passing -along secondary axes form an inverted image of the -same size as the object, when the latter is situated -at twice the focal length of the lens from this last. -To avoid confusion, the bounding lines only are -shown, but similar lines might be drawn from each -and every point of the object; and if the lines -<i>ALA'</i>, <i>BL'B'</i> be supposed to be balanced at <i>L</i> and -<i>L'</i> respectively, they will indicate the points at -which the corresponding parts of the object and<span class="pagenum" title="10"><a name="Page_10" id="Page_10"></a></span> -image will be situated along the lines <i>AB</i>, <i>B'A'</i> -respectively. Moreover, rays pass from every part -of the object to every part of the lens, so that we -must imagine the cones <i>LAL'</i>, <i>LA'L'</i> to be filled -with rays diverging on one side of the lens and -converging on the other.</p> - -<p>The image so formed is a “real” image,—that is -to say, it can be thrown upon a screen.</p> - -<div class="figcenter" style="width: 510px;"> -<a id="Fig_3"></a> -<img src="images/i_010.jpg" width="510" height="196" alt="" /> -<div class="caption"><p><span class="smcap">Fig. 3.</span></p></div> -</div> - -<p>The microscopic image, on the other hand, is -a virtual image, which can be viewed by the eye -but cannot be thus projected, for it is formed by an -object placed nearer to the lens than the principal -focal length of the latter, so that the rays diverge, -instead of converging, as they leave the lens, and the -eye looks, as it were, back along the path in which -the rays appear to travel, and so sees an enlarged -image situated in the air, farther away than the -object, as shown in Fig. <a href="#Fig_4">4</a>. In this case, as the -diagram shows, the image is upright, not inverted.</p> - -<p>Images of the latter class are those formed by -simple microscopes, of the kind described in the -previous chapter. In the compound microscope<span class="pagenum" title="11"><a name="Page_11" id="Page_11"></a></span> -the initial image, formed by the object-glass, is -further magnified by another set of lenses, forming -the eye-piece, by which the diverging rays of the -virtual image are brought together to a focus at -the eye-point; and when viewed directly, the eye -sees an imaginary image, as in a simple microscope, -whilst, when the rays are allowed to fall upon a -screen, they form a real image of the object, larger -or smaller, as the screen is farther from or nearer -to the eye-point.</p> - -<div class="figcenter" style="width: 470px;"> -<a id="Fig_4"></a> -<img src="images/i_011.jpg" width="470" height="288" alt="" /> -<div class="caption"><p><span class="smcap">Fig. 4.</span></p></div> -</div> - -<p>These remarks must suffice for our present -purpose. Those who are sufficiently interested in -the subject to desire to know more of the delicate -corrections to which these broad principles are -subjected in practice, that objectives may give -images which are clear and free from colour, to say -nothing of other faults, will do well to consult some<span class="pagenum" title="12"><a name="Page_12" id="Page_12"></a></span> -such work as Lommel’s <i>Optics</i>, in the International -Science Series.</p> - -<p>In following a work such as the present one, the -simple microscope, in some form or other, will be -found almost indispensable. It will be required -for examining raw material, such as leaves or other -parts of plants, for gatherings of life in fresh or -salt water, for dissections. With such powers as -those with which we shall have to deal, it will -rarely happen that, for example, a bottle of water -in which no life is visible will be worth the -carrying-home; whilst, on the other hand, a few -months’ practice will render it not only possible, -but easy, not only to recognise the presence, but to -identify the genus, and often even the species, of -the forms of life present. Moreover, these low -powers, affording a general view of the object, -allow the relation to each other of the details -revealed by the power of the compound microscope -to be much more easily grasped. A rough example -may suffice to illustrate this. A penny is a sufficiently -evident object to the naked eye, but it will -require a sharp one to follow the details in -Britannia’s shield, whilst the minute scratches -or the bloom upon the surface would be invisible in -detail without optical aid. Conversely, however, -it would be rash to conclude from an examination -of a portion of the surface with the microscope -alone that the portion in view was a sample of the -whole surface. The more the surface is magnified, -the less are the details grasped as a whole, and for -this reason the observer is strongly recommended<span class="pagenum" title="13"><a name="Page_13" id="Page_13"></a></span> -to make out all that he can of an object with a -simple magnifier before resorting to the microscope.</p> - -<p>For general purposes, the intending observer -cannot do better than supply himself with a -common pocket-magnifier, with one, two, or three -lenses, preferably the last, as although the absolute -performance is not so accurate, the very considerable -range of power available by using the lenses -singly, or in various combinations, is of great -advantage. Such a magnifier may be obtained -from Baker for about three-and-sixpence, -or, with the addition -of a powerful Coddington lens -(Fig. <a href="#Fig_5">5</a>) in the same mount, for -nine shillings more. Aplanatic -lenses, such as the one shown in -section in Fig. <a href="#Fig_6">6</a>, with a much -flatter field of vision, but of one -power only each, cost about -fifteen shillings, and a simple -stand, which adapts them for -dissecting purposes, may be obtained -of the same maker for half a crown, or may -easily be extemporised from a cork sliding stiffly -on an iron rod set in a heavy foot, the cork carrying -a loop of wire terminating in a ring which -carries the lens.</p> - -<div class="figcenter" style="width: 150px;"> -<a id="Fig_5"></a> -<img src="images/i_013a.jpg" width="150" height="98" alt="" /> -<div class="caption"><p><span class="smcap">Fig. 5.</span></p></div> -</div> - -<div class="figcenter" style="width: 120px;"> -<a id="Fig_6"></a> -<img src="images/i_013b.jpg" width="120" height="99" alt="" /> -<div class="caption"><p><span class="smcap">Fig. 6.</span></p></div> -</div> - -<p>So much may suffice for the simple microscope. -We pass on now to the consideration of the instrument -which forms the subject of the present work, -an instrument which, whilst moderate in price, is -yet capable of doing a large amount of useful and<span class="pagenum" title="14"><a name="Page_14" id="Page_14"></a></span> -valuable work in the hands of a careful owner, and -of affording him a vast amount of pleasure and recreation, -even if these be his only objects in the -purchase, though it is difficult to understand that, -an insight being once attained into the revelations -effected by the instrument, without a desire being -excited in any intelligent -mind to pursue -the subject as a study -as well as a delightful -relaxation. The microscope -described, and -adopted as his text -by the author of this -work, is still made, -and has shared to a -very considerable extent -in the general -improvement of optical -apparatus which has -taken place during the -last thirty years. It -is to be obtained from -Baker, 244 High Holborn, -and is provided -with most of the apparatus which will be found -indispensable by the beginner, costing, with a case -in which to keep it, the modest sum of three -guineas.</p> - -<div class="figcenter" style="width: 250px;"> -<a id="Fig_7"></a> -<img src="images/i_014.jpg" width="250" height="411" alt="" /> -<div class="caption"><p><span class="smcap">Fig. 7.</span></p></div> -</div> - -<p>If this instrument represent the limit of the -purchaser’s power of purse, he may very well make -it answer his purpose for a considerable time. The<span class="pagenum" title="15"><a name="Page_15" id="Page_15"></a></span> -same instrument, however, with separate objectives -of good quality, together with a bull’s-eye condenser -(an almost indispensable adjunct), a plane mirror in -addition to a concave one, and a simple but efficient -form of substage condenser, may be obtained for -£5, 12s. 6d., -and the extra -outlay will be -well repaid by -the advantage -in working -which is -gained by the -possession of -the additional -apparatus.</p> - -<div class="figcenter" style="width: 330px;"> -<a id="Fig_8"></a> -<img src="images/i_015.jpg" width="330" height="451" alt="" /> -<div class="caption"><p><span class="smcap">Fig. 8.</span></p></div> -</div> - -<p>A still -better stand, -and one -which is good -enough for -almost any -class of work, -is that shown -in Fig. <a href="#Fig_8">8</a>, -which is -known as the “Portable” microscope. In this -instrument the body is made up of two tubes, so -that the length may be varied at will, and this -gives a very considerable range of magnification -without changing the object-glass, a great convenience -in practice; whilst the legs fold up<span class="pagenum" title="16"><a name="Page_16" id="Page_16"></a></span> -for convenience of carriage, so that the whole -instrument, with all necessary appliances, may -be readily packed in a corner of a portmanteau for -transport to the country or seaside.</p> - -<p>The objectives supplied with the simplest form of -microscope above referred to are combinations of -three powers in one, and the power is varied by -using one, two, or three of these in combination. -This form of objective is very good, as far as it -goes, though it is impossible to correct such a combination -with the accuracy which is possible in -manufacturing one of a fixed focal length.</p> - -<p>Perhaps the best thing for the beginner to do -would be to purchase the combination first, and, -later on, to dispose of it and buy separate objectives -of, say, one-inch, half-inch, and quarter-inch focal -lengths. It may be explained here, that when a -lens is spoken of as having a certain focal length, -it is meant that the magnification obtained by its -use is the same, at a distance of ten inches from the<span class="pagenum" title="17"><a name="Page_17" id="Page_17"></a></span> -eye, as would be obtained by using a simple sphere -of glass of the same focal length at the same -distance. This, of course, is simply a matter of -theory, for such lenses are never used actually.</p> - -<div class="figcenter" style="width: 350px;"> -<a id="Fig_9"></a> -<img src="images/i_016.jpg" width="350" height="234" alt="" /> -<div class="caption"><p><span class="smcap">Fig. 9.</span></p></div> -</div> - -<p>Of accessory apparatus, we may mention first the -stage forceps (Fig. <a href="#Fig_9">9</a>, <i>a</i>). These are made to fit into -a hole upon the stage, so as to be capable of being -turned about in any direction, with an object in -their grasp, and for some purposes, especially such -as the examination of a thin object, say the edge of -a leaf, they are extremely -useful.</p> - -<div class="figcenter" style="width: 280px;"> -<a id="Fig_10"></a> -<img src="images/i_017.jpg" width="280" height="187" alt="" /> -<div class="caption"><p><span class="smcap">Fig. 10.</span></p></div> -</div> - -<p>The live box, -in which drops of -water or portions -of water-plants, or -the like, may be -examined, will be -found of great -service. By adjustment -of the -cap upon the cylinder, with proper attention to the -thickness of the cover-glass in the cap, any required -amount of pressure, from that merely sufficient to -fix a restless object to an amount sufficient to crush -a resistent tissue, may easily be applied, whilst the -result of the operation is watched through the -microscope. This proceeding is greatly facilitated -if the cap of the live-box be slotted spirally, with a -stud on the cylinder, so that a half-turn of the cap -brings the glasses into contact. By this means the -pressure may be adjusted with the greatest nicety.</p> - -<p><span class="pagenum" title="18"><a name="Page_18" id="Page_18"></a></span></p> - -<p>In examining delicate objects, such as large infusoria, -which invariably commit suicide when -pressure is applied, a good plan is to restrict their -movements by placing a few threads of cotton-wool, -well pulled out, in the live-box with the drop of -water.</p> - -<p>A variety of instruments has been invented for -the same purpose, of which Beck’s parallel compressorium -may be mentioned as the most efficient, -though it is somewhat complicated, and consequently -expensive, costing about twenty-five shillings.</p> - -<p>A few glass slips and cover-glasses will also be -required. The latter had better be those known as -“No. 2,” since the beginner will find it almost -impossible to clean the thinner ones satisfactorily -without a large percentage of fractures. The safest -way is to boil the thin glass circles in dilute nitric -acid (half acid, half water) for a few minutes, wash -well in several waters, first tap-water and then distilled, -and finally to place the covers in methylated -spirit. When required for use, the spirit may be -burnt off by applying a light, the cover-glass, held -in a pair of forceps, being in no way injured by the -process.</p> - -<p>In addition to the glass slides, the observer will -find it advisable to be provided with a few glass -troughs, of various thicknesses, in which portions of -water-plants, having organisms attached to them, -may be examined. Confined in the live-box, many -of the organisms ordinarily found under such circumstances -can rarely be induced to unfold their beauties, -whilst in the comparative freedom of the trough<span class="pagenum" title="19"><a name="Page_19" id="Page_19"></a></span> -they do so readily. The troughs may be purchased, -or may be made of any desired shape or size by -cutting strips of glass of a thickness corresponding -to the depth desired, cementing these to a glass -slide somewhat larger than the ordinary one, and -cementing over the frame so formed a piece of thin -glass, No. 3; the best material to use as cement -being marine glue of the best quality, or, failing -this, Prout’s elastic glue, which is much cheaper, -but also less satisfactory. The glass surface must -be made, in either case, sufficiently hot to ensure -thorough adhesion of the cement, as the use of any -solvent entails long waiting, and considerable risk -of poisoning the organisms. A useful practical -hint in the use of these troughs is that the corners, -at the top, should be greased slightly, otherwise the -water finds its way out by capillary attraction, -to the detriment of the stage of the microscope.</p> - -<p>Of optical accessories, the bull’s-eye is almost the -most valuable. So much may be effected by its -means alone, in practised hands, that it is well -worth the while of the beginner to master its use -thoroughly, and the methods of doing so will be -explained in the succeeding chapter.</p> - -<p>The substage condenser, too, even in its most -simple form, is an invaluable adjunct, even though -it be only a hemisphere of glass, half an inch or so -in diameter, mounted in a rough sliding jacket to fit -underneath the stage. Such an instrument, properly -fitted, will cost about fifteen shillings, but the ingenious -worker will easily extemporise one for -himself.</p> - -<p><span class="pagenum" title="20"><a name="Page_20" id="Page_20"></a></span></p> - -<div class="figcenter" style="width: 430px;"> -<a id="Fig_11"></a> -<img src="images/i_020.jpg" width="430" height="285" alt="" /> -<div class="caption"><p><span class="smcap">Fig. 11.</span></p></div> -</div> - -<p>Many plants and animals require to be dissected -to a certain extent before the details of their structure -can be made out, and for this purpose the -naked eye alone will rarely serve. The ordinary -pocket magnifier, however, if mounted as described -in a preceding chapter, will greatly facilitate matters, -and the light may be focused upon the object by -means of the bull’s-eye condenser, as shown in -Fig. <a href="#Fig_11">11</a>. In the figure the latter is represented -as used in conjunction with the lamp, but daylight -is preferable if it be available, the strain upon the -eyes being very much less than with artificial light. -Two blocks of wood, about four inches high, will -form convenient rests for the hands, a plate of glass -being placed upon the blocks to support the dish, -and a mirror being put in the interspace at an angle -of 45° or so if required. A piece of black paper<span class="pagenum" title="21"><a name="Page_21" id="Page_21"></a></span> -may be laid upon the mirror if reflected light alone -is to be used.</p> - -<p>As all delicate structures are dissected under fluid, -a shallow dish is required. For this purpose nothing -is better than one of the dishes used for developing -photographic negatives. The bottom of the dish -is occupied by a flat cork, to which a piece of flat -lead is attached below, and the object having been -pinned on to the cork in the required position, the -fluid is carefully run in. This fluid will naturally -vary according to the results desired to be obtained, -but it must not be plain water, which so alters all -cellular structures as to practically make them unrecognisable -under the microscope. Nothing could -be better than a 5 per cent. solution of formalin, -were it not for the somewhat irritating odour of -this fluid, since it at once fixes the cells and preserves -the figure. For many purposes a solution of -salt, in the proportion of a saltspoonful of the -latter to a pint of water, will answer well for short -dissections. For more prolonged ones, a mixture of -spirit-and-water, one part of the former to two of -the latter, answers well, especially for vegetable -structures. When the dilution is first made, the -fluid becomes milky, unless pure spirit be used, but -with a little trouble the Revenue authorities may -be induced to give permission for the use of pure -methylated spirit, which answers every purpose. The -trouble then is that not less than five gallons can be -purchased, an <i>embarras de richesses</i> for the average -microscopist, but, after all, the spirit is extremely -cheap, and does not deteriorate by keeping.</p> - -<p><span class="pagenum" title="22"><a name="Page_22" id="Page_22"></a></span></p> - -<p>When the dissection in either of these media is -completed, spirit should be gradually added to -bring the strength up to 50 per cent., in which -the preparation may remain for a day or two, after -which it is gradually brought into pure spirit, or -into water again, according to the medium in which -it is to be mounted.</p> - -<div class="figcenter" style="width: 380px;"> -<a id="Fig_12"></a> -<img src="images/i_023.jpg" width="380" height="438" alt="" /> -<div class="caption"><p><span class="smcap">Fig. 12.</span></p></div> -</div> - -<p>As to the tools required, they are neither -numerous nor expensive. Fine-pointed but strong -forceps (Fig. <a href="#Fig_9">9</a>, <i>c</i>), curved and straight; a couple of -pairs of scissors, one strong and straight, the other -more delicate, and having curved blades, and a few -needles of various thicknesses and curves, are the -chief ones. The latter may be made by inserting -ordinary needles, for three-fourths of their length, -into sticks of straight-grained deal (ordinary firewood -answers best), and thereafter bending them -as required. A better plan, however, is to be -provided with a few of the needle-holders shown -in Fig. <a href="#Fig_9">9</a>, <i>b</i>. These are very simple and inexpensive, -and in them broken needles are readily -replaced by others. Dipping-tubes, such as are -shown in Fig. <a href="#Fig_12">12</a>, will also be extremely useful -for many purposes. These are very easily made -by heating the centre of a piece of soft glass -tubing of the required size, and, when it is quite -red-hot, drawing the ends apart. The fine tube -in the centre should now be divided by scratching -it with a fine triangular file, and the scratch may -of course be made at such a point as to afford a -tube of the required fineness. The edges should -be smoothed by holding them in the flame until<span class="pagenum" title="23"><a name="Page_23" id="Page_23"></a></span> -they just run (not melt, or the tube will close). -These tubes can often be made to supply the place -of a glass syringe. They may be used either for -sucking up fluid or for transferring it, placing the -finger over the wide end, allowing the tube to fill -by displacement of air, and then re-closing it with -the finger. This last method is especially useful -for transferring small objects from one receptacle -to another. In speaking of the dissection of -objects, it should have been mentioned that the -microscope itself may, under careful handling, be<span class="pagenum" title="24"><a name="Page_24" id="Page_24"></a></span> -made to serve very well, only, as the image is -reversed, it is almost impossible to work without -using a prism to re-erect the image. Such a -prism is shown in Fig. <a href="#Fig_13">13</a>. The microscope is -placed vertically, and the observer, looking straight -into the prism, sees all the parts of the image -in their natural positions. This appliance is -extremely useful for the purpose of selecting -small objects, and arranging them on slides in -any desired manner. A few words may be added -as to the reproduction of the images of objects.</p> - -<div class="figcenter" style="width: 400px;"> -<a id="Fig_13"></a> -<img src="images/i_024.jpg" width="400" height="239" alt="" /> -<div class="caption"><p><span class="smcap">Fig. 13.</span></p></div> -</div> - -<p>The beginner is strongly recommended to -practise himself in this from the outset. Even -a rough sketch is worth pages of description, -especially if the magnification used be appended; -and even though the worker may be devoid of -artistic talent, he will find that with practice he -will acquire a very considerable amount of facility -in giving truthful outlines at least of the objects<span class="pagenum" title="25"><a name="Page_25" id="Page_25"></a></span> -which he views. Various aids have been devised -for the purpose of assisting in the process. The -simplest and cheapest of these consists of a cork -cut so as to fit round the eye-piece. Into the -cork are stuck two pins, at an angle of 45° to -the plane of the cork, and, the microscope being -placed horizontally, a thin cover-glass is placed -upon the two pins, the light being arranged and -the object focused after the microscope is inclined. -On looking vertically down upon the cover-glass, -a bright spot of light will be seen, and as the eye -is brought down into close proximity with it the -spot will expand and allow the observer to see -the whole of the image without looking into the -microscope. If a sheet of paper be now placed -upon the table at the place occupied by the image -so projected, the whole of the details will be -clearly seen, as will also the point of a pencil -placed upon the paper in the centre of the field -of view; and, after a little practice, it will be -found easy to trace round the chief details of the -object. Two points require attention. The first -is that if the light upon the paper be stronger -than that in the apparent field of the microscope, -the image will not be well seen, or if the paper be -too feebly lighted, it will be difficult to keep the -point of the pencil in view. The light from the -microscope is thrown into the eye, and the view -of the image upon the paper is the effect of a -mental act, the eye looking out in the direction -from which the rays appear to come. The paper -has therefore to be illuminated independently, and<span class="pagenum" title="26"><a name="Page_26" id="Page_26"></a></span> -half the battle lies in the adjustment of the -relative brightness of image and paper. The -second point is, that it is essential to fix one -particular point in the image as the starting-point -of the drawing, and this being first depicted, the -image and drawing of this point must be kept -always coincident, or the drawing will be distorted, -since the smallest movement of the eye alters the -relations of the whole. The reflector must be -placed at an angle of 45°, or the field will be -oval instead of circular. The simple form of -apparatus just described has one drawback, inasmuch -as the reflection is double, the front and -back of the cover-glass both acting as reflectors. -The image from the latter being much the more -feeble of the two, care in illumination will do -much to eliminate this difficulty; but there are -various other forms in which the defect in -question is got rid of. The present writer has -worked with all of them, from the simple neutral -tint reflector of Beale to the elaborate and costly -apparatus of Zeiss, and, upon the whole, thinks -that he prefers the cover-glass to them all.</p> - -<p>A very simple plan, not so mechanical as the -last-named, consists in the use of “drawing-squares,” -which are delicate lines ruled upon a -piece of thin glass, and dropped into the eye-piece -so that the lines rest upon the diaphragm -of the eye-piece, and therefore are in focus at the -same time as the object. By the use of these, -in combination with paper similarly ruled, a -diagram of any required size can be drawn with<span class="pagenum" title="27"><a name="Page_27" id="Page_27"></a></span> -very great facility. The squares, if compared with -a micrometer, will furnish an exact standard of -magnitude for each object-glass employed. The -micrometer is a piece of thin glass upon which -are ruled minute divisions of an inch or a millimeter. -Suppose the micrometer to be placed -under the microscope when the squares are in -the eye-piece, and it be found that each division -corresponds with one square of the latter, then, -if the micrometric division be one one-hundredth -of an inch, and the squares upon the paper -measure one inch, it is clear that the drawing -will represent the object magnified a hundred -“diameters”; if two divisions of the micrometer -correspond to three squares, the amplification will -be a hundred and fifty diameters; if three divisions -correspond to two squares, sixty-six diameters, and -so on. If a draw-tube be used, it will be necessary -to know the value of the squares at each inch of -the length, if they are to be used for measuring -magnification.</p> - -<hr class="chap" /> - -<div class="chapter"> -<p><span class="pagenum" title="28"><a name="Page_28" id="Page_28"></a></span></p> - - - - -<h2>CHAPTER III</h2> -</div> - -<p class="subhead">Examination of Objects—Principles of Illumination—Mirror -and its Action—Substage Condenser—Use of Bull’s-eye—Opaque -Objects—Photography of Microscopic Objects.</p> - - -<p>So much depends upon a right method of employing -the microscope, as regards both comfort and -accuracy, that we propose to devote a little space -to the consideration of the subject.</p> - -<p>Let us first warn the intending observer against -the use of powers higher than are required to -bring out the details of the object. Mere magnification -is of very little use: it increases the -difficulties both of illumination and of manipulation, -and, as already said, interferes with that -grasp of the object which it is most desirable -to obtain. Rather let the beginner lay himself -out to get the very most he can out of his -lowest powers, and he will find that, by so doing, -he will be able far better to avail himself of the -higher ones when their use is indispensable.</p> - -<p>The essential means to this end is a mastery of -the principles of illumination, which we now proceed -to describe.</p> - -<p>We suppose the microscope to be inclined at -an angle of about 70° to the horizontal, with a<span class="pagenum" title="29"><a name="Page_29" id="Page_29"></a></span> -low-power objective attached to it, a one-inch by -preference. Opposite to the microscope, and about -a foot away from it, is a lamp with the edge of -the flame presented to the microscope, the concave -mirror of which is so arranged as to receive the -rays from the flame and direct them up the tube -of the microscope. Upon the stage is placed a -piece of ground-glass, and the mirror-arm is now -to be moved up or down upon its support until the -ground-glass receives the maximum of illumination, -which it will do when the lamp-flame is at one -conjugate focus of the mirror and the ground-glass -at the other. The focus will not be an image of -the flame, but a bar of light.</p> - -<p>If an object be now placed upon the stage, -instead of the ground-glass, and the objective -focused upon it, it will, if the mirror be properly -adjusted, be brilliantly illuminated.</p> - -<p>It will be understood that every concave mirror -has a focus, and converges the rays which fall upon -it to this focus, behaving exactly like a convex -lens. The principal focus of a concave mirror is -its radius of curvature, and this is not difficult to -determine. Place side by side a deep cardboard -box and the lamp, so that the concave mirror may -send the rays back, along a path only slightly -inclined to that by which they reached it, to the -bottom of the box. The lamp and box being -equidistant from the mirror, it is evident that -when the mirror forms an image of the former -upon the latter equal to the flame in size, we -have the equivalent of the equal conjugate foci<span class="pagenum" title="30"><a name="Page_30" id="Page_30"></a></span> -shown in Fig. <a href="#Fig_2">2</a>. Now move the box to the -distance from the mirror which corresponds to -the distance of the stage of the microscope from -the mirror when the latter is in position upon -the microscope, and then move the lamp to or -fro until the mirror casts a sharp image of the -flame upon the bottom of the box, which is not -to be moved. The lamp distance so found will be -the correct one for working with the concave -mirror. The writer is led to lay special stress -upon this matter, from the fact that he almost -invariably finds that the mirror is arranged to be -used for parallel rays, <i>i.e.</i> for daylight, and is -therefore fixed far too close to the stage to be -available for correct or advantageous working with -the lamp, unless, indeed, the bull’s-eye condenser -be used, as hereinafter described, to parallelise the -rays from the lamp.</p> - -<p>Work done with the concave mirror can, however, -under the most favourable conditions, only -be looked upon as a <i>pis aller</i>. The advantages -gained by the use of some substage condenser, -even the most simple, in conjunction with the plane -mirror, or even without any mirror at all, are so -manifold that the beginner is strongly urged to -provide himself with some form or other of it, -and we now proceed to describe the way in which -this should be used to produce the best effect.</p> - -<p>To reduce the problem to its most simple -elements, turn the mirror altogether out of the -way, and place the microscope upon a block at -such a height as shall be convenient for observa<span class="pagenum" title="31"><a name="Page_31" id="Page_31"></a></span>tion, -and shall allow the rays from the lamp, -placed in a line with it on the table, to shine -directly into the tube of the microscope. Ascertain -that this is so by removing both objective and -eye-piece and looking down the tube, when the -flame should be seen in the centre, edgewise. -Now replace the eye-piece, and screw on to the -tube the one-inch combination or objective. Place -upon the stage an object, preferably a round diatom -or an echinus-spine, and focus it as sharply as -possible. Now place the substage condenser in its -jacket, and slide it up and down until the image of -the object is bisected by the image of the flame.</p> - -<p>The centre of the object will now be brilliantly -illuminated by rays travelling in the proper direction -for yielding the best results. The object is -situated at the common focus of the microscope and -the condenser, and, whatever means of illumination -be adopted, this is the result which should always -be aimed at.</p> - -<p>Satisfactory as this critical arrangement is, however, -from a scientific point of view, it has its -drawbacks from an artistic and æsthetic one. It -is not pleasant, for most purposes, to have merely -the centre of an object lighted up, and we have -now to consider how the image of the edge of -the flame may be so expanded as to fill the field -without sacrificing more than a very small fraction -of the accuracy of the arrangement just attained.</p> - -<p>Referring to Fig. <a href="#Fig_1">1</a>, we see that if we place -the lamp at the principal focus of a lens, it will -emit a bundle of parallel rays equal in diameter<span class="pagenum" title="32"><a name="Page_32" id="Page_32"></a></span> -to the diameter of the lens. This is the key of -the position. We cannot place the lamp at an -infinite distance from the substage condenser, but -we can supply the latter with rays approximately -parallel, so that it shall bring them to a focus upon -the object at very nearly its own principal focus. -This we do by means of the bull’s-eye condenser. -Place the latter, with its flat side toward the edge -of the flame, and at its principal focal distance -(the method of determining which has already -been described) from the latter, so that the bundle -of parallel rays which issue from it may pass up -to the substage condenser. On examining the -object again, it will be found that, after slight -adjustments of the position of the bull’s-eye have -been made, the object lies in the centre of an -evenly and brilliantly lighted field.</p> - -<p>It may be necessary to place the bull’s-eye a -little farther from or nearer to the lamp, or to -move it a little to one side or the other, but when -it is at the correct distance, and on the central -line between the lamp and the substage condenser, -at right angles to this line, the effects will be as -described. It may help in securing this result if -we mention that when the bull’s-eye is too far -from the lamp, the image of the flame is a spindle-shaped -one; whilst, when the distance between the -two is too short, <i>i.e.</i> less than the principal focal -length of the lens, the field is crossed by a bar -or light, the ends of which are joined by a ring, -whilst on either side of the bar there is a semi-circular -dark space.</p> - -<p><span class="pagenum" title="33"><a name="Page_33" id="Page_33"></a></span></p> - -<p>We have hitherto supposed the objects viewed -to be transparent, but there are many, of great -interest, which are opaque, and call for other -means of illumination. Of these there are several. -The simplest and, in many ways, the best is to -use the bull’s-eye condenser to bring to a focus -upon the object the rays of light from some source -placed above the stage of the microscope. If light -can be obtained from the sun itself, no lens will -be needed to concentrate it; and indeed, if this -were done, there would be considerable risk of -burning the object. The light from a white -cloud, however, with the help of the bull’s-eye, -answers admirably. At night-time an artificial -source of light, the more intense and the more -distant the better, is required. For most cases, -and with powers not higher than one inch, a good -paraffin lamp, placed about two feet away from the -stage, and on one side of it, so as to be about a -foot above the level of the object, will give all -that is needed. Such a lamp is shown in Fig. <a href="#Fig_14">14</a>. -Low magnifications are, as a rule, all that is called -for in this method.</p> - -<p>Lieberkuhn’s condensers are useful aids, but are -somewhat expensive. They are concave mirrors, -which are so adjusted to the objective that the -latter and the reflector come into focus together, -the light being sent in from below, or from one side.</p> - -<p>One other method of illumination must be mentioned -before leaving the topic, and this is the -illumination of objects upon a “dark field.” With -suitable subjects, and when carefully managed,<span class="pagenum" title="34"><a name="Page_34" id="Page_34"></a></span> -there is no method which gives more beautiful -effects, and it has the great advantage of allowing -the object to be brilliantly lighted, without the -strain to the eyes which is involved in such lighting -by the usual method of direct illumination.</p> - -<div class="figcenter" style="width: 590px;"> -<a id="Fig_14"></a> -<img src="images/i_034.jpg" width="590" height="432" alt="" /> -<div class="caption"><p><span class="smcap">Fig. 14.</span></p></div> -</div> - -<p>It consists essentially in allowing the light to -fall upon the object from below, at such an angle -that none of it can enter the objective directly. -Thus the concave mirror, turned as far as possible -to one side, and reflecting on to the object the rays -from the lamp placed upon the opposite side, will<span class="pagenum" title="35"><a name="Page_35" id="Page_35"></a></span> -give very fair results with low powers; this plan, -however, is capable of but very limited application. -Again, a disc of black paper may be stuck on to -the middle of the bull’s-eye, and the latter be -placed below the stage between it and the mirror. -In this case everything depends upon the size of -the disc, which, if too small, will not give a black -ground, and if too large will cut off all light from -the object.</p> - -<p>The best and only really satisfactory plan is to -arrange the illumination with the substage condenser, -as previously described, and then to place -below the lens of the latter a central stop of a -suitable size, which can only be determined by -trial. When this has been done the object will -be seen brilliantly illuminated upon a field of -velvety blackness. Such stops are supplied with -the condenser.</p> - -<p>We have devoted a considerable portion of space -to this question, since it is, of all others, the most -important to a successful, satisfactory, and reliable -manipulation of the microscope; but even now, only -the main points of the subject have been touched -upon, and the worker will find it necessary to -supplement the information given by actual experiment. -A few failures, rightly considered, will -afford a great amount of information, but those -who desire to go thoroughly into the matter are -recommended to consult the present writer’s <i>Guide -to the Science of Photomicrography</i>, where it is -treated at much greater length, as an essential -part of the subject-matter of the book.</p> - -<p><span class="pagenum" title="36"><a name="Page_36" id="Page_36"></a></span></p> - -<p>It may be added here, that no method of reproducing -the images of objects is on the whole so -satisfactory as the photographic one; and whilst a -lengthened reference to the topic would be out of -place in a work of the character of the present one, -the one just mentioned will be found to contain all -that is necessary to enable the beginner to produce -results which, for faithfulness and beauty, far excel -any drawing, whilst they have the additional advantage -that they can, if required, be exhibited to -hundreds simultaneously.</p> - -<hr class="chap" /> - -<div class="chapter"> -<p><span class="pagenum" title="37"><a name="Page_37" id="Page_37"></a></span></p> - - - - -<h2>CHAPTER IV</h2> -</div> - -<p class="subhead">Vegetable Cells and their Structure—Stellate Tissues—Secondary -Deposit—Ducts and Vessels—Wood-Cells—Stomata, -or Mouths of Plants—The Camera Lucida, and -Mode of Using—Spiral and Ringed Vessels—Hairs of -Plants—Resins, Scents, and Oils—Bark Cells.</p> - - -<p>We will now suppose the young observer to have -obtained a microscope and learned the use of its -various parts, and will proceed to work with it. -As with one or two exceptions, which are only -given for the purpose of further illustrating some -curious structure, the whole of the objects figured -in this work can be obtained without any difficulty, -the best plan will be for the reader to procure -the plants, insects, etc., from which the objects are -taken, and follow the book with the microscope at -hand. It is by far the best mode of obtaining a -systematic knowledge of the matter, as the quantity -of objects which can be placed under a microscope is -so vast that, without some guide, the tyro flounders -hopelessly in the sea of unknown mysteries, and -often becomes so bewildered that he gives up the -study in despair of ever gaining any true knowledge -of it. I would therefore recommend the reader to -work out the subjects which are here mentioned,<span class="pagenum" title="38"><a name="Page_38" id="Page_38"></a></span> -and then to launch out for himself on the voyage -of discovery. I speak from experience, having -myself known the difficulties under which a young -and inexperienced observer has to labour in so wide -a field, without any guide to help him to set about -his work in a systematic manner.</p> - -<p>The objects that can be most easily obtained are -those of a vegetable nature, as even in London -there is not a square, an old wall, a greenhouse, a -florist’s window, or even a greengrocer’s shop, that -will not afford an exhaustless supply of microscopic -employment. Even the humble vegetables that -make their daily appearance on the dinner-table -are highly interesting; and in a crumb of potato, a -morsel of greens, or a fragment of carrot, the enthusiastic -observer will find occupation for many hours.</p> - -<p>Following the best examples, we will commence at -the beginning, and see how the vegetable structure is -built up of tiny particles, technically called “cells.”</p> - -<p>That the various portions of every vegetable -should be referred to the simple cell is a matter of -some surprise to one who has had no opportunity -of examining the vegetable structure, and indeed it -does seem more than remarkable that the tough, -coarse bark, the hard wood, the soft pith, the green -leaves, the delicate flowers, the almost invisible -hairs, and the pulpy fruit, should all start from -the same point, and owe their origin to the simple -vegetable cell. This, however, is the case; and by -means of a few objects chosen from different -portions of the vegetable kingdom, we shall obtain -some definite idea of this curious phenomenon.</p> - - -<p class="tac">I.</p> - -<div class="center"> -<table border="0" cellpadding="0" cellspacing="0" summary="Key to Plate I"> -<tr><td class="tar pr05 fs70">FIG.</td></tr> -<tr><td class="tar pr05">1.</td><td class="tal">Strawberry, cellular tissue</td><td class="tar prl05 bl">15.</td><td class="tal">Wood-cells, Elder</td></tr> -<tr><td class="tar pr05">2.</td><td class="tal">Buttercup leaf, internal layer</td><td class="tar prl05 bl">16.</td><td class="tal">Glandular markings and resin, “Cedar” pencil</td></tr> -<tr><td class="tar pr05">3.</td><td class="tal">Privet, Seed Coat, showing star-shaped cells </td><td class="tar prl05 bl">17.</td><td class="tal"> Do.  Yew</td></tr> -<tr><td class="tar pr05">4.</td><td class="tal">Rush, Star-shaped cells</td><td class="tar prl05 bl">18.</td><td class="tal">Scalariform tissue, Stalk of Fern</td></tr> -<tr><td class="tar pr05">5.</td><td class="tal">Mistletoe, cells with ringed fibre</td><td class="tar prl05 bl">19.</td><td class="tal">Dotted Duct, Willow</td></tr> -<tr><td class="tar pr05">6.</td><td class="tal">Cells from interior of Lilac bud</td><td class="tar prl05 bl">20.</td><td class="tal"> Do.  Stalk of Wheat</td></tr> -<tr><td class="tar pr05">7.</td><td class="tal">Bur-reed (<i>Sparganium</i>), square cells from leaf </td><td class="tar prl05 bl">21.</td><td class="tal">Wood-cell, Chrysanthemum</td></tr> -<tr><td class="tar pr05">8.</td><td class="tal">Six-sided cells, from stem of Lily</td><td class="tar prl05 bl">22.</td><td class="tal"> Do.  Lime-tree</td></tr> -<tr><td class="tar pr05">9.</td><td class="tal">Angular dotted cells, rind of Gourd</td><td class="tar prl05 bl">23.</td><td class="tal">Dotted Duct, Carrot</td></tr> -<tr><td class="tar pr05">10.</td><td class="tal">Elongated ringed cells, anther of Narcissus </td><td class="tar prl05 bl">24.</td><td class="tal">Cone-bearing wood, Deal</td></tr> -<tr><td class="tar pr05">11.</td><td class="tal">Irregular star-like tissue, pith of Bulrush</td><td class="tar prl05 bl">25.</td><td class="tal">Cells, outer coat, Gourd</td></tr> -<tr><td class="tar pr05">12.</td><td class="tal">Six-sided cells, pith of elder</td><td class="tar prl05 bl">26.</td><td class="tal">Ducts, Elm</td></tr> -<tr><td class="tar pr05">13.</td><td class="tal">Young cells from Wheat</td><td class="tar prl05 bl">27.</td><td class="tal">Cellular tissue, Stalk of Chickweed</td></tr> -<tr><td class="tar pr05">14.</td><td class="tal"> Do.  rootlets of Wheat</td><td class="tar prl05 bl">28.</td><td class="tal">Holly-berry, outer coat</td></tr> -</table></div> - - -<div class="figcenter" style="width: 441px;"> -<a id="Pl_I"></a> -<img src="images/i_p_001.jpg" width="441" height="700" alt="" /> -<div class="caption"><p>I.</p></div> -</div> - -<p><span class="pagenum" title="39"><a name="Page_39" id="Page_39"></a></span></p> - -<p>On Plate I. Fig. <a href="#Pl_I">1</a>, may be seen three cells of a -somewhat globular form, taken from the common -strawberry. Any one wishing to examine these -cells for himself may readily do so by cutting a -very thin slice from the fruit, putting it on a slide, -covering it with a piece of thin glass (which may -be cheaply bought at the optician’s, together with -the glass slides on which the objects are laid), and -placing it under a power of two hundred diameters. -Should the slice be rather too thick, it may be -placed in the live-box and well squeezed, when the -cells will exhibit their forms very distinctly. In -their primary form the cells seem to be spherical; -but as in many cases they are pressed together, and -in others are formed simply by the process of subdivision, -the spherical form is not very often seen. -The strawberry, being a soft and pulpy fruit, -permits the cells to assume a tolerably regular -form, and they consequently are more or less -globular.</p> - -<p>Where the cells are of nearly equal size, and are -subjected to equal pressure in every direction, they -force each other into twelve-sided figures, having -the appearance under the microscope of flat six-sided -forms. Fig. <a href="#Pl_I">8</a>, in the same Plate, taken from -the stem of a lily, is a good example of this form -of cell, and many others may be found in various -familiar objects.</p> - -<p>We must here pause for a moment to define a -cell before we proceed further.</p> - -<p>The cell is a close sac or bag formed of a -substance called from its function “cellulose,” and<span class="pagenum" title="40"><a name="Page_40" id="Page_40"></a></span> -containing certain semi-fluid contents as long as it -retains its life. In the interior of the cell may -generally be found a little dark spot, termed the -“núcleus,” and which may be seen in Fig. <a href="#Pl_I">1</a>, to -which we have already referred. The object of the -nucleus is rather a bone of contention among the -learned, but the best authorities on this subject -consider it to be the vital centre of the cells, to and -from which tends the circulation of the protoplasm, -and which is intimately connected with the growth -and reproduction of the cell. On looking a little -more closely at the nucleus, we shall find it marked -with several small light spots, which are termed -“nucléoli.”</p> - -<p>On the same Plate (Fig. <a href="#Pl_I">2</a>) is a pretty group of -cells taken from the internal layer of the buttercup -leaf, and chosen because they exhibit the series of -tiny and brilliant green dots to which the colour -of the leaf is due. The technical name for this -substance is “chlorophyll,” or “leaf-green,” and it -may always be found thus dotted in the leaves of -different plants, the dots being very variable in size, -number, and arrangement. A very fine object for -the exhibition of this point is the leaf of <i>Anácharis</i>, -the “Canadian timber-weed,” to be found in almost -every brook and river. It also shows admirably -the circulation of the protoplasm in the cell.</p> - -<p>In the centre of the same Plate (Fig. <a href="#Pl_I">12</a>) is a -group of cells from the pith of the elder-tree. -This specimen is notable for the number of little -“pits” which may be seen scattered across the -walls of the cells, and which resemble holes when<span class="pagenum" title="41"><a name="Page_41" id="Page_41"></a></span> -placed under the microscope. In order to test the -truth of this appearance, the specimen was coloured -blue by the action of iodine and dilute sulphuric -acid, when it was found that the blue tint spread -over the pits as well as the cell-walls, showing -that the membrane is continuous over the pits.</p> - -<p>Fig. <a href="#Pl_I">7</a> exhibits another form of cell, taken from -the Spargánium, or bur-reed. These cells are -tolerably equal in size, and have assumed a square -shape. They are obtained from the lower part of -the leaf. The reader who has any knowledge of -entomology will not fail to observe the similarity -in form between the six-sided and square cells of -plants and the hexagonal and square facets of the -compound eyes of insects and crustaceans. In a -future page these will be separately described.</p> - -<p>Sometimes the cells take most singular and unexpected -shapes, several examples of which will be -briefly noticed.</p> - -<p>In certain loosely made tissues, such as are -found in the rushes and similar plants, the walls of -the cells grow very irregularly, so that they push -out a number of arms which meet each other in -every direction, and assume the peculiar form which -is termed “stellate,” or star-shaped tissue. Fig. <a href="#Pl_I">3</a> -shows a specimen of stellate tissue taken from the -seed-coat of the privet, and rather deeply coloured, -exhibiting clearly the beautiful manner in which -the arms of the various stars meet each other. A -smaller group of stellate cells taken from the stem -of a large rush, and exemplifying the peculiarities -of the structure, are seen in Fig. <a href="#Pl_I">4</a>.</p> - -<p><span class="pagenum" title="42"><a name="Page_42" id="Page_42"></a></span></p> - -<p>The reader will at once see that this mode of -formation leaves a vast number of interstices, and -gives great strength with little expenditure of -material. In water-plants, such as the reeds, this -property is extremely valuable, as they must be -greatly lighter than the water in which they live, -and at the same time must be endowed with -considerable strength in order to resist its -pressure.</p> - -<p>A less marked example of stellate tissue is -given in Fig. <a href="#Pl_I">11</a>, where the cells are extremely -irregular, in their form, and do not coalesce -throughout. This specimen is taken from the -pithy part of a bulrush. There are very many -other plants from which the stellate cells may -be obtained, among which the orange affords very -good examples, in the so-called “white” that lies -under the yellow rind, a section of which may -be made with a very sharp razor, and placed in -the field of the microscope.</p> - -<p>Looking toward the bottom of the Plate, and -referring to Fig. <a href="#Pl_I">27</a>, the reader will observe a -series of nine elongated cells, placed end to end, -and dotted profusely with chlorophyll. These -are obtained from the stalk of the common -chickweed. Another example of the elongated -cell is seen in Fig. <a href="#Pl_I">14</a>, which is a magnified -representation of the rootlets of wheat. Here -the cells will be seen set end to end, and each -containing its nucleus. On the left hand of the -rootlet (Fig. <a href="#Pl_I">13</a>) is a group of cells taken from -the lowest part of the stem of a wheat plant<span class="pagenum" title="43"><a name="Page_43" id="Page_43"></a></span> -which had been watered with a solution of -carmine, and had taken up a considerable amount -of the colouring substance. Many experiments -on this subject were made by the Rev. Lord -S. G. Osborne, and may be seen at full length -in the pages of the <i>Microscopical Journal</i>, the -subject being too large to receive proper treatment -in the very limited space which can here be -given to it. It must be added that later -researches have caused the results here described -to be gravely disputed.</p> - -<p>Fig. <a href="#Pl_I">9</a> on the same Plate exhibits two notable -peculiarities—the irregularity of the cells and -the copiously pitted deposit with which they are -covered. The irregularity of the cells is mostly -produced by the way in which the multiplication -takes place, namely, by division of the original -cell into two or more new ones, so that each of -these takes the shape which it assumed when a -component part of the parent cell. In this case -the cells are necessarily very irregular, and when -they are compressed from all sides they form -solid figures of many sides, which, when cut -through, present a flat surface marked with a -variety of irregular outlines. This specimen is -taken from the rind of a gourd.</p> - -<p>The “pitted” structure which is so well shown -in this figure is caused by a layer of matter -which is deposited in the cell and thickens its -walls, and which is perforated with a number of -very minute holes called “pits.” This substance -is called “secondary deposit.” That these pits do<span class="pagenum" title="44"><a name="Page_44" id="Page_44"></a></span> -not extend through the real cell-wall has already -been shown in Fig. <a href="#Pl_I">12</a>.</p> - -<p>This secondary deposit assumes various forms. -In some cases it is deposited in rings round the -cell, and is clearly placed there for the purpose of -strengthening the general structure. Such an -example may be found in the mistletoe (Fig. <a href="#Pl_I">5</a>), -where the secondary deposit has formed itself -into clear and bold rings that evidently give -considerable strength to the delicate walls which -they support. Fig. <a href="#Pl_I">10</a> shows another good instance -of similar structure; differing from the preceding -specimen in being much longer and containing a -greater number of rings. This object is taken -from an anther of the narcissus. Among the -many plants from which similar objects may be -obtained, the yew is perhaps one of the most -prolific, as ringed wood-cells are abundant in its -formation, and probably aid greatly in giving to -the wood the strength and elasticity which have -long made it so valuable in the manufacture of -bows.</p> - -<p>Before taking leave of the cells and their -remarkable forms, we will just notice one example -which has been drawn in Fig. <a href="#Pl_I">6</a>. This is a -congeries of cells, containing their nuclei, starting -originally end to end, but swelling and dividing -at the top. This is a very young group of cells -(a young hair, in fact) from the inner part of a -lilac bud, and is here introduced for the purpose -of showing the great similarity of all vegetable -cells in their earliest stages of existence.</p> - -<p><span class="pagenum" title="45"><a name="Page_45" id="Page_45"></a></span></p> - -<p>Having now examined the principal forms of -cells, we arrive at the “vessels,” a term which is -applied to those long and delicate tubes which are -formed of a number of cells set end to end, their -walls of separation being absorbed.</p> - -<p>In Fig. <a href="#Pl_I">19</a> the reader will find a curious -example of the “pitted vessel,” so called from the -multitude of little markings which cover its walls, -and are arranged in a spiral order. Like the pits -and rings already mentioned, the dots are composed -of secondary deposit in the interior of the tube, -and vary very greatly in number, function, and -dimensions. This example is taken from the wood -of the willow, and is remarkable for the extreme -closeness with which the dots are packed together.</p> - -<p>Immediately on the right hand of the preceding -figure may be seen another example of a dotted -vessel (Fig. <a href="#Pl_I">20</a>), taken from a wheat stem. In -this instance the cells are not nearly so long, but -are wider than in the preceding example, and are -marked in much the same way with a spiral series -of dots. About the middle of the topmost cell is -shown the short branch by which it communicates -with the neighbouring vessel.</p> - -<p>Fig. <a href="#Pl_I">23</a> exhibits a vessel taken from the common -carrot, in which the secondary deposit is placed in -such a manner as to resemble a net of irregular -meshes wrapped tightly round the vessel. For -this reason it is termed a “netted vessel.” A very -curious instance of these structures is given in -Fig. <a href="#Pl_I">26</a>, at the bottom of the Plate, where are -represented two small vessels from the wood of the<span class="pagenum" title="46"><a name="Page_46" id="Page_46"></a></span> -elm. One of them—that on the left hand—is -wholly marked with spiral deposit, the turns being -complete; while, in the other instance, the spiral -is comparatively imperfect, and the cell-walls are -marked with pits. If the reader would like to -examine these structures more attentively, he will -find plenty of them in many familiar garden -vegetables, such as the common radish, which is -very prolific in these interesting portions of vegetable -nature.</p> - -<p>There is another remarkable form in which this -secondary deposit is sometimes arranged that is -well worthy of our notice. An example of this -structure is given in Fig. <a href="#Pl_I">18</a>, taken from the stalk -of the common fern or brake. It is also found -in very great perfection in the vine. On inspecting -the illustration, the reader will observe -that the deposit is arranged in successive bars -or steps, like those of a winding staircase. In -allusion to the ladder-like appearance of this -formation, it is called “scalariform” (Latin, <i>scala</i>, -a ladder).</p> - -<p>In the wood of the yew, to which allusion has -already been made, there is a very peculiar structure, -a series of pits found only in those trees that -bear cones, and therefore termed the coniferous -pitted structure. Fig. <a href="#Pl_I">16</a> is a section of a common -cedar pencil, the wood, however, not being that of -the true cedar, but of a species of fragrant Juniper. -This specimen shows the peculiar formation which -has just been mentioned.</p> - -<p>Any piece of deal or pine will exhibit the same<span class="pagenum" title="47"><a name="Page_47" id="Page_47"></a></span> -peculiarities in a very marked manner, as is seen in -Fig. <a href="#Pl_I">24</a>. A specimen may be readily obtained by -making a very thin shaving with a sharp plane. -In this example the deposit has taken a partially -spiral form, and the numerous circular pits with -which it is marked are only in single rows. In -several other specimens of coniferous woods, such -as the Araucaria, or Norfolk Island pine, there are -two or three rows of pits.</p> - -<p>A peculiarly elegant example of this spiral deposit -may be seen in the wood of the common yew (Fig. <a href="#Pl_I">17</a>). -If an exceedingly thin section of this wood be made, -the very remarkable appearance will be shown which -is exhibited in the illustration. The deposit has not -only assumed the perfectly spiral form, but there -are two complete spirals, arranged at some little -distance from each other, and producing a very -pretty effect when seen through a good lens.</p> - -<p>The pointed, elongated shape of the wood-cells -is very well shown in the common elder-tree (see -Fig. <a href="#Pl_I">15</a>). In this instance the cells are without -markings, but in general they are dotted like Fig. <a href="#Pl_I">21</a>, -an example cut from the woody part of the chrysanthemum -stalk. This affords a very good instance of -the wood-cell, as its length is considerable, and both -ends are perfect in shape. On the right hand of -the figure is a drawing of the wood-cell found in the -lime-tree (Fig. <a href="#Pl_I">22</a>), remarkable for the extremely -delicate spiral markings with which it is adorned. -In these wood-cells the secondary deposit is so -plentiful that the original membranous character of -the cell-walls is entirely lost, and they become elongated<span class="pagenum" title="48"><a name="Page_48" id="Page_48"></a></span> -and nearly solid cases, having but a very small -cavity in their centre. It is to this deposit that the -hardness of wood is owing, and the reader will easily -see the reason why the old wood is so much harder -than the young and new shoots. In order to permit -the passage of the fluids which maintain the life of -the part, it is needful that the cell-wall be left thin -and permeable in certain places, and this object is -attained either by the “pits” described on page <a href="#Page_43">43</a>, -or by the intervals between the spiral deposit.</p> - -<p>At the right-hand bottom corner of Plate I. (Fig. <a href="#Pl_I">28</a>) -may be seen a prettily marked object, which is -of some interest. It is a slice stripped from the -outer coat of the holly-berry, and is given for the -purpose of illustrating the method by which plants -are enabled to breathe the atmospheric air on which -they depend as much as ourselves, though their -respiration is slower. Among the mass of net-like -cells may be seen three curious objects, bearing a -rather close resemblance to split kidneys. These -are the mouths, or “stómata,” as they are scientifically -called.</p> - -<p>In the centre of the mouths may be seen a dark -spot, which is the aperture through which the air -communicates with the passages between the cells -in the interior of the structure. In the flowering -plants their shape is generally rounded, though they -sometimes take a squared form, and they regularly -occur at the meeting of several surface cells. The -two kidney-shaped cells which form the “mouth” -are the “guard-cells,” so called from their function, -since, by their change of form, they cause the mouth<span class="pagenum" title="49"><a name="Page_49" id="Page_49"></a></span> -to open or shut, according to the needs of the plant. -In young plants these guard-cells are very little below -the surface of the leaf or skin, but in others they -are sunk quite beneath the layer of cells forming -the outer coat of the tissue. There are other -cases where they are slightly elevated above the -surface.</p> - -<p>Stomata are found chiefly in the green portions -of plants, and are most plentiful on the under side of -leaves. It is, however, worthy of notice, that when -an aquatic leaf floats on the water, the mouths are -only to be found on the upper surface. These -curious and interesting objects are to be seen in -many structures where we should hardly think of -looking for them; for instance, they may be found -existing on the delicate skin which envelops the -kernel of the common walnut. As might be expected, -their dimensions vary with the character of -the leaf on which they exist, being large upon the -soft and pulpy leaves, and smaller upon those of a -hard and leathery consistence. The reader will find -ample amusement, and will gain great practical -knowledge of the subject, by taking a plant, say a -tuft of groundsel, and stripping off portions of the -external skin or “epidermis” from the leaf or stem, -etc., so as to note the different sizes and shapes of -the stomata.</p> - -<p>On the opposite bottom corner of Plate I. Fig. <a href="#Pl_I">25</a>, -is an example of a stoma taken from the outer skin -of a gourd, and here given for the purpose of showing -the curious manner in which the cells are -arranged about the mouth, no less than seven cells<span class="pagenum" title="50"><a name="Page_50" id="Page_50"></a></span> -being placed round the single mouth, and the -others arranged in a partially circular form around -them.</p> - -<p>Turning to Plate II., we find several other examples -of stomata, the first of which (Fig. <a href="#Pl_II">1</a>) is -obtained from the under surface of the buttercup -leaf, by stripping off the external skin, or “epidermis,” -as it is scientifically termed. The reader will -here notice the slightly waved outlines of the cell-walls, -together with the abundant spots of chlorophyll -with which the leaf is coloured. In this -example the stomata appear open. Their closure -or expansion depends chiefly on the state of the -weather; and, as a general rule, they are open by -day and closed at night.</p> - -<p>A remarkably pretty example of stomata and -elongated cells is to be obtained from the leaf of the -common iris, and may be prepared for the microscope -by simply tearing off a strip of the epidermis -from the under side of the leaf, laying it on a slide, -putting a little water on it, and covering it with a -piece of thin glass. (See Plate II. Fig. <a href="#Pl_II">2</a>.) There -are a number of longitudinal bands running along -the leaf where these cells and stomata appear. -The latter are not placed at regular intervals, for it -often happens that the whole field of the microscope -will be filled with cells without a single stoma, whilst -elsewhere a group of three or four may be seen -clustered closely together.</p> - -<p>Fig. <a href="#Pl_II">3</a> on the same Plate exhibits a specimen of -the beautifully waved cells, without mouths, which -are found on the upper surface of the ivy leaf.<span class="pagenum" title="51"><a name="Page_51" id="Page_51"></a></span> -These are difficult to arrange from the fresh leaf, -but are easily shown by steeping the leaf in water -for some time, and then tearing away the cuticle. -The same process may be adopted with many leaves -and cuticles, and in some cases the immersion must -be continued for many days, and the process of -decomposition aided by a very little nitric acid in -the water, or by boiling.</p> - -<p>On the same Plate are three examples of spiral -and ringed vessels, types of an endless variety of -these beautiful and interesting structures. Fig. <a href="#Pl_II">4</a> -is a specimen of a spiral vessel taken from the lily, -and is a beautiful example of a double spire. The -deposit which forms this spiral is very strong, and -it is to the vast number of these vessels that the -stalk owes its well-known elasticity. In many cases -the spiral vessels are sufficiently strong to be visible -to the naked eye, and to bear uncoiling. For -example, if a leaf-stalk of geranium be broken -across, and the two fragments gently drawn asunder, -a great number of threads, drawn from the spiral -vessels, will be seen connecting the broken ends. -In this case the delicate membranous walls of the -vessel are torn apart, and the stronger fibre which -is coiled spirally within it unrolls itself in proportion -to the force employed. In many cases these -fibres are so strong that they will sustain the weight -of an inch or so of the stalk.</p> - -<p>In Fig. <a href="#Pl_II">5</a> is seen a still more bold and complex -form of this curious structure; being a coil of five -threads, laid closely against each other, and forming, -while remaining in their natural position, an almost<span class="pagenum" title="52"><a name="Page_52" id="Page_52"></a></span> -continuous tube. This specimen is taken from the -root of the water lily, and requires some little care -to exhibit its structure properly.</p> - -<p>Every student of nature must be greatly struck -with the analogies between different portions of the -visible creation. These spiral structures which we -have just examined are almost identical in appearance, -and to some extent in their function, with -the threads that are coiled within the breathing -tubes of insects. This is in both cases twofold, -namely, to give support and elasticity to a delicate -membrane, and to preserve the tube in its proper -form, despite the bending to which it may be -subjected. When we come to the anatomy of the -insect in a future page we shall see this structure -further exemplified.</p> - -<p>In some cases the deposit, instead of forming a -spiral coil, is arranged in a series of rings, and the -vessel is then termed “annulated.” A very good -example of this formation is given in Fig. <a href="#Pl_II">6</a>, which -is a sketch of such a vessel, taken from a stalk of -the common rhubarb. To see these ringed vessels -properly, the simplest plan is to boil the rhubarb -until it is quite soft, then to break down the pulpy -mass until it is flattened, to take some of the most -promising portions with the forceps, lay them on -the slide and press them down with a thin glass -cover. They will not be found scattered at random -through the fibres, which elsewhere present only -a congeries of elongated cells, but are seen grouped -together in bundles, and with a little trouble may -be well isolated, and the pulpy mass worked away -so as to show them in their full beauty. As may -be seen in the illustration, the number of the rings -and their arrangement is extremely variable. A -better, but somewhat more troublesome, plan is to -cut longitudinal sections of the stem, as described -in our concluding chapter, when not only the -various forms of cells and vessels, but their -relations to each other, will be well shown. The -numerous crystals of oxalate of lime, which make -rhubarb so injurious a food for certain persons, -will also be well seen. These crystals are called -“raphides,” and are to be found in very many -plants in different forms.</p> - - -<p class="tac">II.</p> - -<div class="center"> -<table border="0" cellpadding="0" cellspacing="0" summary="Key to Plate II"> -<tr><td class="tar pr05 fs70">FIG.</td></tr> -<tr><td class="tar pr05">1.</td><td class="tal">Cuticle, Buttercup leaf</td><td class="tar prl05 bl">24.</td><td class="tal"> Do.  Pine cone</td></tr> -<tr><td class="tar pr05">2.</td><td class="tal"> Do.  Iris</td><td class="tar prl05 bl">25.</td><td class="tal">Vitta, Caraway Seed</td></tr> -<tr><td class="tar pr05">3.</td><td class="tal"> Do.  Ivy leaf</td><td class="tar prl05 bl">26.</td><td class="tal">Cork</td></tr> -<tr><td class="tar pr05">4.</td><td class="tal">Spiral vessel, Lily</td><td class="tar prl05 bl">27.</td><td class="tal">Hair, Flower of Garden Verbena</td></tr> -<tr><td class="tar pr05">5.</td><td class="tal"> Do.  root, (rhizome) Water Lily </td><td class="tar prl05 bl">28.</td><td class="tal"> Do.  fruit of Plane</td></tr> -<tr><td class="tar pr05">6.</td><td class="tal">Ringed vessel, Rhubarb</td><td class="tar prl05 bl">29.</td><td class="tal"> Do.  do.</td></tr> -<tr><td class="tar pr05">7.</td><td class="tal">Chaff, after burning</td><td class="tar prl05 bl">30.</td><td class="tal"> Do.  do.</td></tr> -<tr><td class="tar pr05">8.</td><td class="tal">Bifid hair, Arabis</td><td class="tar prl05 bl">31.</td><td class="tal"> Do.  Lobelia</td></tr> -<tr><td class="tar pr05">9.</td><td class="tal">Hair, Marvel of Peru</td><td class="tar prl05 bl">32.</td><td class="tal"> Do.  Cabbage</td></tr> -<tr><td class="tar pr05">10.</td><td class="tal">End of hair, leaf of Hollyhock</td><td class="tar prl05 bl">33.</td><td class="tal"> Do.  Dead-nettle flower</td></tr> -<tr><td class="tar pr05">11.</td><td class="tal">Hair, Sowthistle leaf</td><td class="tar prl05 bl">34.</td><td class="tal"> Do.  Garden Verbena flower</td></tr> -<tr><td class="tar pr05">12.</td><td class="tal"> Do.  Tobacco</td><td class="tar prl05 bl">35.</td><td class="tal">Fruit-hair, Dandelion</td></tr> -<tr><td class="tar pr05">13.</td><td class="tal"> Do.  Southernwood</td><td class="tar prl05 bl">36.</td><td class="tal">Hair, Thistle leaf</td></tr> -<tr><td class="tar pr05">14.</td><td class="tal">Group of hairs, Hollyhock leaf</td><td class="tar prl05 bl">37.</td><td class="tal"> Do.  Cactus</td></tr> -<tr><td class="tar pr05">15.</td><td class="tal">Hair, Yellow Snapdragon</td><td class="tar prl05 bl">38.</td><td class="tal"> Do.  do.</td></tr> -<tr><td class="tar pr05">16.</td><td class="tal"> Do.  Moneywort</td><td class="tar prl05 bl">39.</td><td class="tal"> Do.  Virginian Spider-wort</td></tr> -<tr><td class="tar pr05">17.</td><td class="tal">Hair, Geum</td><td class="tar prl05 bl">40.</td><td class="tal"> Do.  Lavender</td></tr> -<tr><td class="tar pr05">18.</td><td class="tal"> Do.  Flower of Heartsease</td><td class="tar prl05 bl">41.</td><td class="tal">Section, Lavender leaf, Hairs</td></tr> -<tr><td class="tar pr05">19.</td><td class="tal"> Do.  Dockleaf</td><td class="tar prl05 bl"></td><td class="tal">   and perfume-gland</td></tr> -<tr><td class="tar pr05">20.</td><td class="tal"> Do.  Throat of Pansy</td><td class="tar prl05 bl">42.</td><td class="tal">Section, Orange Peel</td></tr> -<tr><td class="tar pr05">21.</td><td class="tal"> Do.  Dead-nettle Flower</td><td class="tar prl05 bl">43.</td><td class="tal">Sting of Nettle</td></tr> -<tr><td class="tar pr05">22.</td><td class="tal"> Do.  Groundsel</td><td class="tar prl05 bl">44.</td><td class="tal">Hair, Marigold flower</td></tr> -<tr><td class="tar pr05">23.</td><td class="tal">Cell, Beech-nut</td><td class="tar prl05 bl">45.</td><td class="tal"> Do.  Ivy</td></tr> -</table></div> - - -<div class="figcenter" style="width: 447px;"> -<a id="Pl_II"></a> -<img src="images/i_p_002.jpg" width="447" height="700" alt="" /> -<div class="caption"><p>II.</p></div> -</div> - -<p><span class="pagenum" title="53"><a name="Page_53" id="Page_53"></a></span></p> - -<p>The hairs of plants form very interesting -objects, and are instructive to the student, as they -afford valuable indications of the mode in which -plants grow. They are all appendages of and arise -from the skin or epidermis; and although their -simplest form is that of a projecting and elongated -cell, the variety of shapes which are assumed by -these organs is inexhaustible. On Plate <a href="#Pl_II">II</a>. are -examples of some of the more striking forms, -which will be briefly described.</p> - -<p>The simple hair is well shown in Figs. 18, 19, -and 32, the first being from the flower of the -heartsease, the second from a dock-leaf, and the -third from a cabbage. In Fig. <a href="#Pl_II">18</a> the hair is seen -to be but a single projecting cell, consisting only of -a wall and the contents. In Fig. <a href="#Pl_II">19</a> the hair has -become more decided in shape, having assumed a -somewhat dome-like form; and in Fig. <a href="#Pl_II">32</a> it has<span class="pagenum" title="54"><a name="Page_54" id="Page_54"></a></span> -become considerably elongated, and may at once be -recognised as a true hair.</p> - -<p>In Fig. <a href="#Pl_II">8</a> is a curious example of a hair taken -from the white Arabis, one of the cruciferous -flowers, which is remarkable for the manner in -which it divides into two branches, each spreading -in opposite directions. Another example of a -forked hair is seen in Fig. <a href="#Pl_II">13</a>, but in this instance -the hair is composed of a chain of cells, the three -lower forming the stem of the hair, and the two -upper being lengthened into the lateral branches. -This hair is taken from the common southernwood.</p> - -<p>In most cases of long hairs, the peculiar elongation -is formed by a chain of cells, varying greatly -in length and development. Several examples of -these hairs will be seen on the same Plate.</p> - -<p>Fig. <a href="#Pl_II">9</a> is a beaded hair from the Marvel of Peru, -which is composed of a number of separate cells -placed end to end, and connected by slender threads -in a manner that strongly reminds the observer of -a chain of beads strung loosely together, so as to -show the thread by which they are connected with -each other. Another good example is seen at -Fig. <a href="#Pl_II">11</a>, in a hair taken from the leaf of the sowthistle. -In this case the beads are strung closely -together, and when placed under a rather high -power of the microscope have a beautifully white -and pearly aspect. The leaf must be dry and quite -fresh, and the hairs seen against the green of the -leaf. Fig. <a href="#Pl_II">39</a> represents another beaded hair taken -from the Virginian Spiderwort, or Tradescantia. -This hair is found upon the stamens, and is<span class="pagenum" title="55"><a name="Page_55" id="Page_55"></a></span> -remarkable for the beautifully beaded outline, the -fine colouring, and the spiral markings with which -each cell is adorned.</p> - -<p>A still further modification of these many-celled -hairs is found in several plants, where the hairs -are formed by a row of ordinarily shaped cells, -with the exception of the topmost cell, which is -suddenly elongated into a whip-like form. Fig. <a href="#Pl_II">22</a> -represents a hair of this kind, taken from the -common groundsel; and Fig. <a href="#Pl_II">36</a> is a still more -curious instance, found upon the leaf of the thistle. -The reader may have noticed the peculiar white -“fluffy” appearance of the thistle leaf when it is -wet after a shower of rain. This appearance is -produced by the long lash-like ends of the hairs, -which are bent down by the weight of the moisture, -and lie almost at right angles with the thicker -portions of the hair.</p> - -<p>An interesting form of hair is seen in the -“sting” of the common nettle. This may readily -be examined by holding a leaf edgewise in the -stage forceps, and laying it under the field of the -microscope. In order to get the proper focus -throughout the hair, the finger should be kept -upon the screw movement, and the hair brought -gradually into focus from its top to its base. The -general structure of this hair is not unlike that -which characterises the fang of a venomous serpent. -The acrid fluid which causes the pain is situated in -the enlarged base of the hair, and is forced through -the long straight tubular extremity by means of -the pressure exerted when the sting enters the<span class="pagenum" title="56"><a name="Page_56" id="Page_56"></a></span> -skin. At the very extremity of the perfect sting -is a slight bulb-like swelling, which serves to -confine the acrid juice, and which is broken -off on the least pressure. The sting is seen in -Fig. <a href="#Pl_II">43</a>.</p> - -<p>The extremities of many hairs present very -curious forms, some being long and slender, as in -the examples already mentioned, while others are -tipped with knobs, bulbs, clubs, or rosettes in -endless variety.</p> - -<p>Fig. <a href="#Pl_II">12</a> is a hair of the tobacco leaf, exhibiting -the two-celled gland at the tip, containing the -peculiar principle of the plant, known by the name -of “nicotine.” The reader will see how easy it is -to detect adulteration of tobacco by means of the -microscope. The leaves most generally used for -this purpose are the dock and the cabbage, so that -if a very little portion of leaf be examined the -character of the hairs will at once inform the -observer whether he is looking at the real article -or its substitute.</p> - -<p>Fig. <a href="#Pl_II">15</a> is a hair from the flower of the common -yellow snapdragon, which is remarkable for the -peculiar shape of the enlarged extremity, and for -the spiral markings with which it is decorated. -Fig. <a href="#Pl_II">16</a> is a curious little knobbed hair found -upon the moneywort, and Fig. <a href="#Pl_II">17</a> is an example -of a double-knobbed hair taken from the Geum. -Fig. <a href="#Pl_II">34</a> affords a very curious instance of a -glandular hair, the stem being built up of cells -disposed in a very peculiar fashion, and the -extremity being developed into a beautiful rosette-<span class="pagenum" title="57"><a name="Page_57" id="Page_57"></a></span>shaped -head. This hair came from the Garden -Verbena.</p> - -<p>Curiously branched hairs are not at all uncommon, -and some very good and easily obtained -examples are given on Plate II.</p> - -<p>Fig. <a href="#Pl_II">28</a> is one of the multitude of branched hairs -that surround the well-known fruit of the plane-tree, -the branches being formed by some of the -cells pointing outward. These hairs do not assume -precisely the same shape; for Fig. <a href="#Pl_II">29</a> exhibits -another hair from the same locality, on which the -spikes are differently arranged, and Fig. <a href="#Pl_II">30</a> is a -sketch of another such hair, where the branches -have become so numerous and so well developed -that they are quite as conspicuous as the parent -stem.</p> - -<p>One of the most curious and interesting forms -of hair is that which is found upon the lavender -leaf, and which gives it the peculiar bloom-like -appearance on the surface.</p> - -<p>This hair is represented in Figs. 40 and 41. -On Fig. <a href="#Pl_II">40</a> the hair is shown as it appears when -looking directly upon the leaf, and in Fig. <a href="#Pl_II">41</a> -a section of the leaf is given, showing the mode in -which the hairs grow into an upright stem, and -then throw out horizontal branches in every -direction. Between the two upright hairs, and -sheltered under their branches, may be seen a -glandular appendage not unlike that which is -shown in Fig. <a href="#Pl_II">16</a>. This is the reservoir containing -the perfume, and it is evidently placed under the -spreading branches for the benefit of their shelter.<span class="pagenum" title="58"><a name="Page_58" id="Page_58"></a></span> -On looking upon the leaf by reflected light the -hairs are beautifully shown, extending their arms -on all sides; and the globular perfume cells may -be seen scattered plentifully about, gleaming like -pearls through the hair-branches under which they -repose. They will be found more numerous on the -under side of the leaf.</p> - -<p>This object will serve to answer a question which -the reader has probably put to himself ere this, -namely, Where are the fragrant resins, scents, and -oils stored? On Plate I. Fig. <a href="#Pl_I">16</a>, will be seen the -reply to the first question; Fig. <a href="#Pl_II">41</a> of the present -Plate has answered the second question, and Fig. <a href="#Pl_II">42</a> -will answer the third. This figure represents a -section of the rind of an orange, the flattened cells -above constituting the delicate yellow skin, and the -great spherical object in the centre being the reservoir -in which the fragrant essential oil is stored. -The covering is so delicate that it is easily broken, -so that even by handling an orange some of the -scent is sure to come off on the hands, and when -the peel is stripped off and bent double, the reservoirs -burst in myriads, and fling their contents -to a wonderful distance. This may be easily seen -by squeezing a piece of orange peel opposite a lighted -candle, and noting the distance over which the oil -will pass before reaching the flame, and bursting -into little flashes of light. Other examples are -given on the same plate.</p> - -<p>Returning to the barbed hairs, we may see in -Fig. <a href="#Pl_II">35</a> a highly magnified view of the “pappus” -hair of a dandelion, <i>i.e.</i> the hairs which fringe the<span class="pagenum" title="59"><a name="Page_59" id="Page_59"></a></span> -arms of the parachute-like appendage which is -attached to the seed. The whole apparatus will -be seen more fully on Plate III. Figs. <a href="#Pl_III">44</a>, 45, 46. -This hair is composed of a double layer of elongated -cells lying closely against each other, and having -the ends of each cell jutting out from the original -line. A simpler form of a double-celled, or more -properly a “duplex” hair, will be seen in Fig. <a href="#Pl_II">44</a>. -This is one of the hairs from the flower of the -marigold and has none of the projecting ends to -the cells.</p> - -<p>In some instances the cell-walls of the hairs -become greatly hardened by secondary deposit, and -the hairs are then known as spines. Two examples -of these are seen in Figs. <a href="#Pl_II">37</a> and 38, the former -being picked from the Indian fig-cactus, and well -known to those persons who have been foolish -enough to handle the fig roughly before feeling it. -The wounds which these spines will inflict are said -to be very painful, and have been compared to -those produced by the sting of the wasp. The -latter hair is taken from the Opuntia. These spines -must not be confounded with thorns; which latter -are modified branches.</p> - -<p>Fig. <a href="#Pl_II">10</a> represents the extreme tip of a hair from -the hollyhock leaf, subjected to a lens of very high -power.</p> - -<p>Many hairs assume a star-like appearance, an -aspect which may be produced in different ways. -Sometimes a number of simple hairs start from the -same base, and by radiating in different directions -produce the stellate effect. An example of this<span class="pagenum" title="60"><a name="Page_60" id="Page_60"></a></span> -kind of hair may be seen in Fig. <a href="#Pl_II">14</a>, which is a -group of hairs from the hollyhock leaf. There is -another mode of producing the star-shape which -may be seen in Fig. <a href="#Pl_II">45</a>, a hair taken from the leaf -of the ivy. Very fine examples may also be found -upon the leaf of Deutzia scabra.</p> - -<p>Hairs are often covered with curious little -branches or protuberances, and present many other -peculiarities of form which throw a considerable -light upon certain problems in scientific microscopy.</p> - -<p>Fig. <a href="#Pl_II">33</a> represents a hair of two cells taken -from the flower of the well-known dead-nettle, -which is remarkable for the number of knobs -scattered over its surface. A similar mode of -marking is seen in Fig. <a href="#Pl_II">31</a>, a club-shaped hair -covered with external projections, found in the -flower of the Lobelia. In order to exhibit these -markings well, a power of two hundred diameters -is needed. Fig. <a href="#Pl_II">21</a> shows this dotting in another -hair from the dead-nettle, where the cell is drawn -out to a great length, but is still covered with these -markings.</p> - -<p>Fig. <a href="#Pl_II">20</a> is an example of a very curious hair -taken from the throat of the pansy. This hair -may readily be obtained by pulling out one of the -petals, when the hairs will be seen at its base. -Under the microscope it has a particularly beautiful -appearance, looking just like a glass walking-stick -covered with knobs, not unlike those huge, knobby -club-like sticks in which some farmers delight, -where the projections have been formed by the -pressure of a honeysuckle or other climbing plant.</p> - -<p><span class="pagenum" title="61"><a name="Page_61" id="Page_61"></a></span></p> - -<p>A hair of a similar character, but even more -curious, is found in the same part of the flower of -the Garden Verbena (see Fig. <a href="#Pl_II">27</a>), and is not only -beautifully translucent, but is coloured according to -the tint of the flower from which it is taken. Its -whole length is covered with large projections, the -joints much resembling the antennæ of certain -insects; and each projection is profusely spotted -with little dots, formed by elevation of the outer -skin or cuticle. These are of some value in determining -the structure of certain appearances upon -petals and other portions of the flowers, and may be -compared with Figs. 33 to 35 on Plate <a href="#Pl_III">III</a>.</p> - -<p>Fig. <a href="#Pl_II">26</a> offers an example of the square cells -which usually form the bark of trees. This is a -transverse section of cork, and perfectly exhibits -the form of bark cells. The reader is very strongly -advised to cut a delicate section of the bark of -various trees, a matter very easily accomplished -with the aid of a sharp razor and a steady hand.</p> - -<p>Fig. <a href="#Pl_II">24</a> is a transverse section through one of the -scales of a pine-cone, and is here given for the -purpose of showing the numerous resin-filled cells -which it displays. This may be compared with -Fig. <a href="#Pl_I">16</a> of Plate I. Fig. <a href="#Pl_II">25</a> is a part of one of -the “vittæ,” or oil reservoirs, from the fruit of the -caraway, showing the cells containing the globules -of caraway oil. This is rather a curious object, -because the specimen from which it was taken was -boiled in nitric acid, and yet retained some of the -oil globules. Immediately above it may be seen -(Fig. <a href="#Pl_II">23</a>) a transverse section of the beechnut,<span class="pagenum" title="62"><a name="Page_62" id="Page_62"></a></span> -showing a cell with its layers of secondary -deposit.</p> - -<p>In the cuticle of the grasses and the mare’s-tails -is deposited a large amount of pure flint. So -plentiful is this substance, and so equally is it -distributed, that it can be separated by heat or -acids from the vegetable parts of the plant, and -will still preserve the form of the original cuticle, -with its cell-walls, stomata, and hairs perfectly well -defined.</p> - -<p>Fig. <a href="#Pl_II">7</a>, Plate II., represents a piece of wheat -chaff, or “bran,” that has been kept at a white heat -for some time, and then mounted in Canada balsam. -I prepared the specimen from which the drawing -was made by laying the chaff on a piece of -platinum, and holding it over the spirit-lamp. A -good example of the silex or flint in wheat is often -given by the remains of a straw fire, where the -stems may be seen still retaining their tubular form -but fused together into a hard glassy mass. It is -this substance that cuts the fingers of those who -handle the wild grasses too roughly, the edges of -the blades being serrated with flinty teeth, just like -the obsidian swords of the ancient Mexicans, or the -shark’s-tooth falchion of the New Zealander.</p> - -<p>These are but short and meagre accounts of a -very few objects, but space will not permit of -further elucidation, and the purpose of this little -work is not to exhaust the subjects of which it -treats, but to incite the reader to undertake investigation -on his own account, and to make his -task easier than if he had done it unaided.</p> - -<hr class="chap" /> - -<div class="chapter"> -<p><span class="pagenum" title="63"><a name="Page_63" id="Page_63"></a></span></p> - - - - -<h2>CHAPTER V</h2> -</div> - -<p class="tac">Starch, its Growth and Properties—Surface Cells of Petals—Pollen -and its Functions—Seeds.</p> - - -<p>The white substance so dear to the laundries under -the name of starch is found in a vast variety of -plants, being distributed more widely than most of -the products which are found in the interior of -vegetable cells.</p> - -<p>The starch grains are of very variable size even -in the same plant, and their form is as variable as -their size, though there is a general resemblance in -those of the same plant which allows of their being -fairly easily identified after a moderate amount of -practice. Sometimes the grains are found loosely -packed in the interior of the cells, and are then -easily recognised as starch grains by their peculiar -form and the delicate lines with which they are -marked; but in many places they are pressed so -closely together that they assume an hexagonal -shape under the microscope, and bear a close resemblance -to ordinary twelve-sided cells. In other -plants, again, the grains never advance beyond the -very minute form in which they seem to commence -their existence; and in some, such as the common -oat, a great number of very little granules are<span class="pagenum" title="64"><a name="Page_64" id="Page_64"></a></span> -compacted together so as to resemble one large -grain.</p> - -<p>There are several methods of detecting starch in -those cases where its presence is doubtful; and the -two modes that are usually employed are polarised -light and the iodide of potassium. When polarised -light is employed—a subject on which we shall -have something to say presently—the starch grains -assume the characteristic “black-cross,” and when -a plate of selenite is placed immediately beneath -the slide containing the starch grains, they glow -with all the colours of the rainbow. The second -plan is to treat them with a very weak solution of -iodine and iodide of potassium, and in this case the -iodine has the effect on the starch granules of -staining them blue. They are so susceptible of -this reaction that when the liquid is too strong the -grains actually become black from the amount of -iodine which they imbibe.</p> - -<p>Nothing is easier than to procure starch granules -in the highest perfection. Take a raw potato, and -with a razor cut a very thin slice from its interior, -the direction of the cut not being of the slightest -importance. Put this delicate slice upon a slide, -drop a little water upon it, cover it with a piece of -thin glass, give it a good squeeze, and place it -under a power of a hundred or a hundred and fifty -diameters. Any part of the slice, provided that it -be very thin, will then present the appearance -shown in Plate III. Fig. <a href="#Pl_III">9</a>, where an ordinary cell -of potato is seen filled loosely with starch grains -of different sizes. Around the edges of the slice a -vast number of starch granules will be seen, which -have been squeezed out of their cells by pressure, -and are now floating freely in the water. As cold -water has no perceptible effect upon starch, the -grains are not altered in form by the moisture, and -can be examined at leisure.</p> - - -<p class="tac">III.</p> - -<div class="center"> -<table border="0" cellpadding="0" cellspacing="0" summary="Key to Plate III"> -<tr><td class="tar pr05 fs70">FIG.</td></tr> -<tr><td class="tar pr05">1.</td><td class="tal">Laurel leaf, transverse section</td><td class="tar prl05 bl">27.</td><td class="tal"> Do.  Heath, another species</td></tr> -<tr><td class="tar pr05">2.</td><td class="tal">Starch, Wheat</td><td class="tar prl05 bl">28.</td><td class="tal">Pollen, Furze</td></tr> -<tr><td class="tar pr05">3.</td><td class="tal"> Do.  from Pudding</td><td class="tar prl05 bl">29.</td><td class="tal"> Do.  Tulip</td></tr> -<tr><td class="tar pr05">4.</td><td class="tal"> Do.  Potato</td><td class="tar prl05 bl">30.</td><td class="tal">Petal, Pelargonium</td></tr> -<tr><td class="tar pr05">5.</td><td class="tal">Outer Skin, Capsicum pod</td><td class="tar prl05 bl">31.</td><td class="tal"> Do.  Periwinkle</td></tr> -<tr><td class="tar pr05">6.</td><td class="tal">Starch, Parsnip</td><td class="tar prl05 bl">32.</td><td class="tal"> Do.  Golden Balsam</td></tr> -<tr><td class="tar pr05">7.</td><td class="tal"> Do.  Arrow Root, West Indian</td><td class="tar prl05 bl">33.</td><td class="tal"> Do.  Snapdragon</td></tr> -<tr><td class="tar pr05">8.</td><td class="tal"> Do.  “Tousles Mois”</td><td class="tar prl05 bl">34.</td><td class="tal"> Do.  Primrose</td></tr> -<tr><td class="tar pr05">9.</td><td class="tal"> Do.  in cell of Potato</td><td class="tar prl05 bl">35.</td><td class="tal"> Do.  Scarlet Geranium</td></tr> -<tr><td class="tar pr05">10.</td><td class="tal"> Do.  Indian Corn </td><td class="tar prl05 bl">36.</td><td class="tal">Pollen, Crocus</td></tr> -<tr><td class="tar pr05">11.</td><td class="tal"> Do.  Sago</td><td class="tar prl05 bl">37.</td><td class="tal"> Do.  Hollyhock</td></tr> -<tr><td class="tar pr05">12.</td><td class="tal"> Do.  Tapioca</td><td class="tar prl05 bl">38.</td><td class="tal">Fruit, Galium, Goosegrass</td></tr> -<tr><td class="tar pr05">13.</td><td class="tal">Root, Yellow Water-Lily</td><td class="tar prl05 bl">39.</td><td class="tal">A hook of ditto more magnified</td></tr> -<tr><td class="tar pr05">14.</td><td class="tal">Starch, Rice</td><td class="tar prl05 bl">40.</td><td class="tal">Seed, Red Valerian</td></tr> -<tr><td class="tar pr05">15.</td><td class="tal"> Do.  Horsebean</td><td class="tar prl05 bl">41.</td><td class="tal">Portion of Parachute of same, more magnified</td></tr> -<tr><td class="tar pr05">16.</td><td class="tal"> Do.  Oat</td><td class="tar prl05 bl">42.</td><td class="tal">Seed, Foxglove</td></tr> -<tr><td class="tar pr05">17.</td><td class="tal">Pollen, Snowdrop</td><td class="tar prl05 bl">43.</td><td class="tal"> Do.  Sunspurge</td></tr> -<tr><td class="tar pr05">18.</td><td class="tal"> Do.  Wallflower</td><td class="tar prl05 bl">44.</td><td class="tal">Parachute, Dandelion seed</td></tr> -<tr><td class="tar pr05">19.</td><td class="tal"> Do.  Willow Herb, a pollen tube </td><td class="tar prl05 bl">45.</td><td class="tal">Seed, Dandelion</td></tr> -<tr><td class="tar pr05">20.</td><td class="tal"> Do.  Violet</td><td class="tar prl05 bl">46.</td><td class="tal"> Do.  Hair of Parachute</td></tr> -<tr><td class="tar pr05">21.</td><td class="tal"> Do.  Musk Plant</td><td class="tar prl05 bl">47.</td><td class="tal"> Do.  Yellow Snapdragon</td></tr> -<tr><td class="tar pr05">22.</td><td class="tal"> Do.  Apple</td><td class="tar prl05 bl">48.</td><td class="tal"> Do.  Mullein</td></tr> -<tr><td class="tar pr05">23.</td><td class="tal"> Do.  Dandelion</td><td class="tar prl05 bl">49.</td><td class="tal"> Do.  Robin Hood</td></tr> -<tr><td class="tar pr05">24.</td><td class="tal"> Do.  Sowthistle</td><td class="tar prl05 bl">50.</td><td class="tal"> Do.  Bur-reed</td></tr> -<tr><td class="tar pr05">25.</td><td class="tal"> Do.  Lily</td><td class="tar prl05 bl">51.</td><td class="tal"> Do.  Willow Herb</td></tr> -<tr><td class="tar pr05">26.</td><td class="tal"> Do.  Heath</td><td class="tar prl05 bl">52.</td><td class="tal"> Do.  Musk Mallow</td></tr> -</table></div> - - -<div class="figcenter" style="width: 447px;"> -<a id="Pl_III"></a> -<img src="images/i_p_003.jpg" width="447" height="700" alt="" /> -<div class="caption"><p>III.</p></div> -</div> - -<p><span class="pagenum" title="65"><a name="Page_65" id="Page_65"></a></span></p> - -<p>On focusing with great care, the surface of each -granule will be seen to be covered with very minute -dark lines, arranged in a manner which can be -readily comprehended from Fig. <a href="#Pl_III">4</a>, which represents -two granules of potato starch as they appear when -removed from the cell in which they took their -origin. All the lines evidently refer to the little -dark spots at the end of the granule, called -technically the “hilum,” and represent the limits of -successive layers of material deposited one after -another. The lines in question are very much -better seen if the substage condenser be used with -a small central stop, so as to obtain partial dark-field -illumination. Otherwise they are often very -difficult of detection.</p> - -<p>In the earliest stages of their growth the starch -granules appear to be destitute of these markings, -or at all events they are so few and so delicate as -not to be visible even with the most perfect instruments, -and it is not until the granules assume -a comparatively large size that the external markings -become distinctly perceptible.</p> - -<p>We will now glance at the examples of starch -which are given in the Plate, and which are a very -few out of the many that might be figured. Fig. <a href="#Pl_III">2</a> -represents the starch of wheat, the upper grain<span class="pagenum" title="66"><a name="Page_66" id="Page_66"></a></span> -being seen in front, the one immediately below it -in profile, and the two others being examples of -smaller grains. Fig. <a href="#Pl_III">6</a> is a specimen of a very -minute form of starch, where the granules do not -seem to advance beyond their earliest stage. This -specimen is obtained from the parsnip; and although -the magnifying power is very great, the -dimensions of the granules are exceedingly small, -and except by a very practised eye they would not -be recognisable as starch grains.</p> - -<p>Fig. <a href="#Pl_III">3</a> is a good example of a starch grain of -wheat, exemplifying the change that takes place -by the combined effects of heat and moisture. It -has already been observed that cold water exercises -little, if any, perceptible influence upon starch; but -it will be seen from the illustration that hot water -has a very powerful effect. When subjected to the -action of water at a temperature over 140° Fahr., -the granule swells rapidly, and at last bursts, the -contents escaping in a gelatinous mass, and the -external membrane collapsing into the form which -is shown in Fig. <a href="#Pl_III">3</a>, which was taken out of a piece -of hot pudding. A similar form of wheat starch -may also be detected in bread, accompanied, unfortunately, -by several other substances not generally -presumed to be component parts of the “staff of life.”</p> - -<p>In Fig. <a href="#Pl_III">7</a> are represented some grains of starch -from West Indian arrowroot, and Fig. <a href="#Pl_III">8</a> exhibits -the largest kind of starch grain known, obtained -from the tuber of a species of canna, supposed to -be <i>C. edúlis</i>, a plant similar in characteristics to -the arrowroot. The popular name of this starch is<span class="pagenum" title="67"><a name="Page_67" id="Page_67"></a></span> -“Tous les Mois,” and under that title it may be -obtained from the opticians, or chemists.</p> - -<p>Fig. <a href="#Pl_III">10</a> shows the starch granules from Indian -corn, as they appear before they are compressed -into the honeycomb-like structure which has -already been mentioned. Even in that state, -however, if they are treated with iodine, they -exhibit the characteristics of starch in a very -perfect manner. Fig. <a href="#Pl_III">11</a> is starch from sago, and -Fig. <a href="#Pl_III">12</a> from tapioca, and in both these instances -the several grains have been injured by the heat -employed in preparing the respective substances -for the market.</p> - -<p>Fig. <a href="#Pl_III">13</a> exhibits the granules obtained from the -root of the water-lily, and Fig. <a href="#Pl_III">14</a> is a good -example of the manner in which the starch granules -of rice are pressed together so as to alter the -shape and puzzle a novice. Fig. <a href="#Pl_III">16</a> is the compound -granule of the oat, which has already been -mentioned, together with some of the simple -granules separated from the mass; and Fig. <a href="#Pl_III">15</a> -is an example of the starch grains obtained from -the underground stem of the horse-bean. It is -worthy of mention that the close adhesion of the -rice starch into those masses is the cause of the -peculiar grittiness which distinguishes rice flour to -the touch.</p> - -<p>Whilst very easily acted on by heat, starch-granules -are very resistent to certain other -reagents. Weak alkalies, in watery solution, -readily attack them, but by treating portions of -plants with caustic potash dissolved in strong<span class="pagenum" title="68"><a name="Page_68" id="Page_68"></a></span> -spirit, the woody and other parts may be dissolved -away; and after repeated washing with spirit the -starch may be mounted. This, however, must -never be in any glycerine medium, except that -given on p. <a href="#Page_172">172</a>.</p> - -<p class="mt2em">In Plate III. Fig. <a href="#Pl_III">1</a>, may be seen a curious little -drawing, which is a sketch of the laurel-leaf cut -transversely, and showing the entire thickness of -the leaf. Along the top may be seen the delicate -layer of “varnish” with which the surface of the -leaf is covered, and which serves to give to the -foliage its peculiar polish. This varnish is nothing -more than the translucent matter which binds all -the cells together, and which is poured out very -liberally upon the surface of the leaf. The lower -part of this section exhibits the cells of which the -leaf is built, and towards the left hand may be seen -a cut end of one of the veins of the leaf, more -rightly called a wood-cell.</p> - -<p>We will now examine a few examples of surface -cells.</p> - -<p>Fig. <a href="#Pl_III">5</a> is a portion of epidermis stripped from a -Capsicum pod, exhibiting the remains of the nuclei -in the centre of each cell, together with the great -thickening of the wall-cells and the numerous pores -for the transmission of fluid. This is a very pretty -specimen for the microscope, as it retains its bright -red colour, and even in old and dried pods exhibits -the characteristic markings.</p> - -<p>In the centre of the Plate may be seen a wheel-like -arrangement of the peculiar cells found on the<span class="pagenum" title="69"><a name="Page_69" id="Page_69"></a></span> -petals of six different flowers, all easily obtainable, -and mounted without difficulty.</p> - -<p>Fig. <a href="#Pl_III">30</a> is the petal of a geranium (Pelargonium), -a very common object on purchased slides. It is -a most lovely subject for the microscope, whether -it be examined with a low or a high power,—in -the former instance exhibiting a most beautiful -“stippling” of pink, white, and black, and in the -latter showing the six-sided cells with their curious -markings.</p> - -<p>In the centre of each cell is seen a radiating -arrangement of dark lines with a light spot in the -middle, looking very like the mountains on a map. -These lines were long thought to be hairs; but -Mr. Tuffen West, in an interesting and elaborate -paper on the subject, has shown their true nature. -From his observations it seems that the beautiful -velvety aspect of flower petals is owing to these -arrangements of the surface cells, and that their -rich brilliancy of colour is due to the same cause. -The centre of each cell-wall is elevated as if pushed -up by a pointed instrument from the under side of -the wall, and in different flowers this elevation -assumes different forms. Sometimes it is merely -a slight wart on the surface, sometimes it becomes -a dome, while in other instances it is so developed -as to resemble a hair. Indeed, Mr. West has concluded -that these elevations are nothing more than -rudimentary hairs.</p> - -<p>The dark radiating lines are shown by the same -authority to be formed by wrinkling of the -membrane forming the walls of the elevated<span class="pagenum" title="70"><a name="Page_70" id="Page_70"></a></span> -centre, and not to be composed of “secondary -deposit,” as has generally been supposed.</p> - -<p>Fig. <a href="#Pl_III">31</a> represents the petal of the common -periwinkle, differing from that of the geranium by -the straight sides of the cell-walls, which do not -present the toothed appearance so conspicuous in -the former flower. A number of little tooth-like -projections may be seen on the interior of the cells, -their bases affixed to the walls and their points -tending toward the centre, and these teeth are, -according to Mr. West, formed of secondary -deposit.</p> - -<p>In Fig. <a href="#Pl_III">32</a> is shown the petal of the common -garden balsam, where the cells are elegantly -waved on their outlines, and have plain walls. -The petal of the primrose is seen in Fig. <a href="#Pl_III">34</a>, and -that of the yellow snapdragon in Fig. <a href="#Pl_III">33</a>; in the -latter instance the surface cells assume a most -remarkable shape, running out into a variety of -zigzag outlines that quite bewilders the eye when -the object is first placed under the microscope. -Fig. <a href="#Pl_III">35</a> is the petal of the common scarlet -geranium.</p> - -<p>In several instances these petals are too thick -to be examined without some preparation, and -glycerine will be found well adapted for that -purpose. The young microscopist must, however, -beware of forming his ideas from preparations of -dried leaves, petals, or hairs, and should always -procure them in their fresh state whenever he -desires to make out their structure. Even a fading -petal should not be used, and if the flowers are<span class="pagenum" title="71"><a name="Page_71" id="Page_71"></a></span> -gathered for the occasion, their stalks should be -placed in water, so as to give a series of leaves and -petals as fresh as possible.</p> - -<p class="mt2em">We now pass from the petal of the flower to the -pollen, that coloured dust, generally yellow or -white, which is found upon the stamens, and which -is very plentiful in many flowers, such as the lily -and the hollyhock.</p> - -<p>This substance is found only upon the stamens -or anthers of full-blown flowers (the anthers being -the male organs), and is intended for the purpose -of enabling the female portion of the flower to -produce fertile seeds. In form the pollen grains -are wonderfully diverse, affording an endless variety -of beautiful shapes. In some cases the exterior is -smooth and marked only with minute dots, but in -many instances the outer wall of the pollen grain -is covered with spikes, or decorated with stripes or -belts. A few examples of the commonest forms of -pollen will be found on Plate III.</p> - -<p>Fig. <a href="#Pl_III">17</a> is the pollen of the snowdrop, which, as -will be seen, is covered with dots and marked with -a definite slit along its length. The dots are -simply tubercles in the outer coat of the grain, and -are presumed to be formed for the purpose of -strengthening the membrane, otherwise too delicate, -upon the same principle which gives to “corrugated” -iron such strength in proportion to the amount of -material. Fig. <a href="#Pl_III">18</a> is the pollen of the wall-flower, -shown in two views, and having many of the same -characteristics as that of the snowdrop. <span class="pagenum" title="72"><a name="Page_72" id="Page_72"></a></span>Fig. <a href="#Pl_III">19</a> -is the pollen of the willow-herb, and is here given -as an illustration of the manner in which the -pollen aids in the germination of plants.</p> - -<p>In order to understand its action, we must first -examine its structure.</p> - -<p>All pollen-grains are furnished with some means -by which their contents when thoroughly ripened -can be expelled. In some cases this end is accomplished -by sundry little holes called pores; in -others, certain tiny lids are pushed up by the -contained matter; and in some, as in the present -instance, the walls are thinned in certain places so -as to yield to the internal pressure.</p> - -<p>When a ripe pollen-grain falls upon the stigma -of a flower, it immediately begins to swell, and -seems to “sprout” like a potato in a damp cellar, -sending out a slender “pollen-tube” from one or -other of the apertures already mentioned. In -Fig. <a href="#Pl_III">19</a> a pollen-tube is seen issuing from one -of the projections, and illustrates the process better -than can be achieved by mere verbal description. -The pollen-tubes insinuate themselves between the -cells of the stigmas, and, continually elongating, -worm their way down the “style” until they come -in contact with the “ovules.” By very careful -dissection of a fertilised stigma, the beautiful sight -of the pollen-tubes winding along the tissues of the -style may be observed under a high power of the -microscope.</p> - -<p>The pollen-tube is nothing more than the interior -coat of the grain, very much developed, and filled -with a substance technically named “fovilla,” composed<span class="pagenum" title="73"><a name="Page_73" id="Page_73"></a></span> -of “protoplasm” (the semi-liquid substance -which is found in the interior of cells), very minute -starch grains, and some apparently oily globules.</p> - -<p>In order to examine the structure of the pollen-grains -properly, they should be examined under -various circumstances—some dry, others placed in -water to which a little sugar has been added, others -in oil, and it will often be found useful to try the -effect of different acids upon them.</p> - -<p>Fig. <a href="#Pl_III">20</a> is the pollen of the common violet, and -is easily recognisable by its peculiar shape and -markings. Fig. <a href="#Pl_III">21</a> is the pollen of the musk-plant, -and is notable for the curious mode in which its -surface is belted with wide and deep bands, running -spirally round the circumference. Fig. <a href="#Pl_III">22</a> -exhibits the pollen of the apple, and Fig. <a href="#Pl_III">23</a> -affords a very curious example of the raised -markings upon the surface of the dandelion pollen. -In Fig. <a href="#Pl_III">24</a> there are also some very wonderful -markings, but they are disposed after a different -fashion, forming a sort of network upon the surface, -and leaving several large free spaces between -the meshes. The pollen of the lily is shown in -Fig. <a href="#Pl_III">25</a>, and is a good example of a pollen-grain -covered with the minute dottings which have -already been described.</p> - -<p>Figs. <a href="#Pl_III">26</a> and 27 show two varieties of compound -pollen, found in two species of heath. These -compound pollen-grains are not of unfrequent occurrence, -and are accounted for in the following manner.</p> - -<p>The pollen is formed in certain cavities within the -anthers, by means of the continual subdivision of<span class="pagenum" title="74"><a name="Page_74" id="Page_74"></a></span> -the “parent-cells” from which it is developed. In -many cases the form of the grain is clearly owing -to the direction in which these cells have divided, -but there is no great certainty on this subject. -It will be seen, therefore, that if the process of -subdivision be suddenly arrested, the grains will -be found adhering to each other in groups of -greater or smaller size, according to the character -of the species and the amount of subdivision that -has taken place. The reader must, however, bear -in mind that the whole subject is as yet rather -obscure, and that further discovery may throw -doubt on many theories which at present are -accepted as established.</p> - -<p>Fig. <a href="#Pl_III">28</a> shows the pollen of the furze, in which -are seen the longitudinal slits and the numerous dots -on the surface; and Fig. <a href="#Pl_III">29</a> is the curiously shaped -pollen of the tulip. The two large yellow globular -figures at each side of the Plate represent the pollen -of two common flowers; Fig. <a href="#Pl_III">36</a> being that of the -crocus, and Fig. <a href="#Pl_III">37</a> a pollen-grain of the hollyhock. -As may be seen from the illustration, the latter -is of considerable size, and is covered with very -numerous projections. These serve to raise the -grain from a level surface, over which it rolls -with a surprising ease of motion, so much so indeed -that if a little of this substance be placed on -a slide and a piece of thin glass laid over it, the -glass slips off as soon as it is in the least inclined, -and forces the observer to fix it with paper or -cement before he can place it on the inclined -stage of the microscope. The little projections<span class="pagenum" title="75"><a name="Page_75" id="Page_75"></a></span> -have a very curious effect under a high power, -and require careful focusing to observe them -properly; for the diameter of the grain is so large -that the focus must be altered to suit each individual -projection. Their office is, probably, to aid -in fertilisation.</p> - -<p class="mt2em">The seeds of plants are even easier of examination -than the pollen, and in most cases require -nothing but a pocket lens and a needle for making -out their general structure. The smaller seeds, -however, must be placed under the microscope, -many of them exhibiting very curious forms. The -external coat of seeds is often of great interest, -and needs to be dissected off before it can be -rightly examined. The simplest plan in such a -case is to boil the seed well, press it while still -warm into a plate of wax, and then dissect with a -pair of needles, forceps, and scissors under water. -Many seeds may also be mounted in cells as dry -objects, after being thoroughly dried themselves.</p> - -<p>A few examples of the seeds of common plants -are given at the bottom of Plate III.</p> - -<p>Fig. <a href="#Pl_III">38</a> exhibits the fruit, popularly called the -seed, of the common goosegrass, or Galium, which -is remarkable for the array of hooklets with which -it is covered. Immediately above the figure may -be seen a drawing of one of the hooks much -magnified, showing its sharp curve (Fig. <a href="#Pl_III">39</a>). It -is worthy of remark that the hook is not a simple -curved hair, but a structure composed of a number -of cells terminating in a hook.</p> - -<p><span class="pagenum" title="76"><a name="Page_76" id="Page_76"></a></span></p> - -<p>Fig. <a href="#Pl_III">40</a> shows the seed, or rather the fruit, of -the common red valerian, and is introduced for the -purpose of showing its plumed extremity, which -acts as a parachute, and causes it to be carried -about by the wind until it meets with a proper -resting-place. It is also notable for the series of -strong longitudinal ribs which support its external -structure. On Fig. <a href="#Pl_III">41</a> is shown a portion of one -of the parachute hairs much more magnified.</p> - -<p>The seed of the common dandelion, so dear to -children in their play-hours, when they amuse -themselves by puffing at the white plumy globes -which tip the ripe dandelion flower-stalks, is a very -interesting object even to their parents, on account -of its beautiful structure, and the wonderful way -in which it is adapted to the place which it fills. -Fig. <a href="#Pl_III">45</a> represents the seed portion of one of these -objects, together with a part of the parachute -stem, the remainder of that appendage being shown -lying across the broken stem.</p> - -<p>The shape of the seed is not unlike that of the -valerian, but it is easily distinguished from that -object by the series of sharp spikes which fringe -its upper end, and which serve to anchor the seed -firmly as soon as it touches the ground. From -this end of the seed proceeds a long slender shaft, -crowned at its summit by a radiating plume of -delicate hairs, each of which is plentifully jagged -on its surface, as may be seen in Fig. <a href="#Pl_III">46</a>, which -shows a small portion of one of these hairs greatly -magnified. These jagged points are evidently intended -to serve the same purpose as the spikes<span class="pagenum" title="77"><a name="Page_77" id="Page_77"></a></span> -below, and to arrest the progress of the seed as -soon as it has found a convenient spot.</p> - -<p>Fig. <a href="#Pl_III">42</a> is the seed of the foxglove, and Fig. <a href="#Pl_III">43</a> -the seed of the sunspurge, or milkwort. Fig. <a href="#Pl_III">47</a> -shows the seed of the yellow snapdragon; remarkable -for the membranous wing with which the seed -is surrounded, and which is composed of cells with -partially spiral markings. When viewed edgewise, -it looks something like Saturn with his ring, or, to -use a more homely but perhaps a more intelligible -simile, like a marble set in the middle of a penny. -Fig. <a href="#Pl_III">48</a> is a seed of mullein, covered with net-like -markings on its external surface. These are probably -to increase the strength of the external coat, -and are generally found in the more minute seeds.</p> - -<p>On Fig. <a href="#Pl_III">50</a> is shown a seed of the burr-reed; a -structure which is remarkable for the extraordinary -projection of the four outer ribs, and their powerful -armature of reverted barbs. Fig. <a href="#Pl_III">51</a> shows another -form of parachute seed, found in the willow-herb, -where the parachute is not expanded nearly so -widely as that of the valerian; neither is it set -upon a long slender stem like that of the dandelion, -but proceeds at once from the top of the seed, -widening towards the extremity, and having a very -comet-like appearance. Two more seeds only remain, -Fig. <a href="#Pl_III">49</a> being the seed of Robin Hood, and -the other, Fig. <a href="#Pl_III">52</a>, that of the muskmallow, being -given in consequence of the thick coat of hairs with -which it is covered.</p> - -<p>Many seeds can be well examined when mounted -in Canada balsam.</p> - -<hr class="chap" /> - -<div class="chapter"> -<p><span class="pagenum" title="78"><a name="Page_78" id="Page_78"></a></span></p> - - - - -<h2>CHAPTER VI</h2> -</div> - -<p class="subhead">Algæ and their Growth—Desmidiaceæ, where found—Diatoms, -their Flinty Deposit—Volvox—Mould, Blight, -and Mildew—Mosses and Ferns—Mare’s-Tail and the -Spores—Common Sea-weeds and their Growth.</p> - - -<p>On Plate <a href="#Pl_IV">IV</a>. will be seen many examples of the -curious vegetables called respectively algæ and -fungi, which exhibit some of the lowest forms of -vegetable life, and are remarkable for their almost -universal presence in all parts of this globe, and -also almost all conditions of cold, heat, or climate. -Many of them are well known under the popular -name of sea-weeds, others are equally familiar -under the titles of “mould,” “blight,” or “mildew,” -while many of the minuter kinds exhibit such -capability of motion, and such apparent symptoms -of volition, that they have long been described as -microscopic animalcules, and thought to belong to -the animal rather than to the vegetable kingdoms.</p> - -<p>Fig. <a href="#Pl_IV">1</a> represents one of the very lowest forms -of vegetable life, being known to the man of science -as the Palmella, and to the general public as -“gory dew.” It may be seen on almost any damp -wall, extending in red patches of various sizes, -looking just as if some blood had been dashed on<span class="pagenum" title="79"><a name="Page_79" id="Page_79"></a></span> -the wall, and allowed to dry there. With a -tolerably powerful lens this substance can be -resolved into the exceedingly minute cells depicted -in the figure. Generally, these cells are single, but -in many instances they are double, owing to the -process of subdivision by which the plant grows, if -such a term may be used.</p> - -<p>Fig. <a href="#Pl_IV">2</a> affords an example of another very low -form of vegetable, the Palmoglæa, that green slimy -substance which is so common on damp stones. -When placed under the microscope, this plant is -resolvable into a multitude of green cells, each -being surrounded with a kind of gelatinous substance. -The mode of growth of this plant is very -simple. A line appears across one of the cells, and -after a while it assumes a kind of hour-glass aspect, -as if a string had been tied tightly round its middle. -By degrees the cell fairly divides into two parts, -and then each part becomes surrounded with its -own layer of gelatine, so as to form two separate -cells, placed end to end.</p> - -<p>One of the figures, that on the right hand, -represents the various processes of “conjugation,” -<i>i.e.</i> the union and fusion together of two cells. -Each cell throws out a little projection; these meet -together, and then uniting, form a sort of isthmus -connecting the two main bodies. This rapidly -widens, until the two cells become fused into one -large body. The whole subject of conjugation is -very interesting, and is treated at great length in the -<i>Micrographic Dictionary</i> of Messrs. Griffith and -Henfrey, a work to which the reader is referred<span class="pagenum" title="80"><a name="Page_80" id="Page_80"></a></span> -for further information on many of the subjects -that, in this small work, can receive but a very -hasty treatment.</p> - -<p>Few persons would suppose that the slug-like -object on Fig. <a href="#Pl_IV">3</a>, the little rounded globules with a -pair of hair-like appendages, and the round disc -with a dark centre, are only different forms of the -same organism. Such, however, is the case, and -these are three of the modifications which the -Protococcus undergoes. This vegetable may be -seen floating like green froth on the surface of -rain-water.</p> - -<p>On collecting some of this froth and putting it -under the microscope, it is seen to consist of a vast -number of little green bodies, moving briskly about -in all directions, and guiding their course with such -apparent exercise of volition that they might very -readily be taken for animals. It may be noticed -that the colour of the plant is sometimes red, and -in that state it has been called the Hæmatococcus.</p> - -<p>The “still” state of this plant is shown in the -round disc. After a while the interior substance -splits into two portions; these again subdivide, and -the process is repeated until sixteen or thirty-two -cells become developed out of the single parent-cell. -These little ones then escape, and, being furnished -with two long “cilia” or thread-like appendages, -whirl themselves merrily through the water. -When they have spent some time in this state, -growing all the while, they lose their cilia, become -clothed with a strong envelope, and pass into the -still stage from which they had previously emerged. -This curious process is repeated in endless succession, -and causes a very rapid growth of the plant. The -moving bodies are technically called zoospores, or -living spores, and are found in many other plants -besides those of the lowest order.</p> - - -<p class="tac">IV.</p> - -<div class="center"> -<table border="0" cellpadding="0" cellspacing="0" summary="Key to Plate IV"> -<tr><td class="tar pr05 fs70">FIG.</td></tr> -<tr><td class="tar pr05">1.</td><td class="tal">Gory Dew, Palmella cruenta</td><td class="tar prl05 bl"></td><td class="tal"> Do.  single green body, above</td></tr> -<tr><td class="tar pr05">2.</td><td class="tal">Palmoglæa macrococca</td><td class="tar prl05 bl">23.</td><td class="tal">Synedra</td></tr> -<tr><td class="tar pr05">3.</td><td class="tal">Protococcus pluvialis,</td><td class="tar prl05 bl">24.</td><td class="tal">Gomphonema acuminatum</td></tr> -<tr><td class="tar pr05"></td><td class="tal"> <i>a</i>, in its motile,</td><td class="tar prl05 bl"></td><td class="tal">  Do.  larger frustules, below</td></tr> -<tr><td class="tar pr05"></td><td class="tal"> <i>b</i>, in its fixed state,</td><td class="tar prl05 bl">25.</td><td class="tal">Yeast</td></tr> -<tr><td class="tar pr05"></td><td class="tal"> <i>c</i>, zoospores</td><td class="tar prl05 bl">26.</td><td class="tal">Sarcina ventriculi</td></tr> -<tr><td class="tar pr05">4.</td><td class="tal">Closterium</td><td class="tar prl05 bl">27.</td><td class="tal">Eunotia diadema</td></tr> -<tr><td class="tar pr05">5.</td><td class="tal">Ditto, end more magnified</td><td class="tar prl05 bl">28.</td><td class="tal">Melosira varians</td></tr> -<tr><td class="tar pr05">6.</td><td class="tal">Pediastrum</td><td class="tar prl05 bl"></td><td class="tal">  Do.  two bleached frustules</td></tr> -<tr><td class="tar pr05">7.</td><td class="tal">Scenedesmus</td><td class="tar prl05 bl">29.</td><td class="tal">Cocconeis pediculus</td></tr> -<tr><td class="tar pr05">8.</td><td class="tal">Oscillatoria</td><td class="tar prl05 bl">30.</td><td class="tal">Achnanthes exilis</td></tr> -<tr><td class="tar pr05">9.</td><td class="tal">Spirogyra</td><td class="tar prl05 bl">31.</td><td class="tal">Navicula amphisbœna</td></tr> -<tr><td class="tar pr05">10.</td><td class="tal">Tyndaridea</td><td class="tar prl05 bl">32.</td><td class="tal">Uredo, “Red-rust” of corn</td></tr> -<tr><td class="tar pr05">11.</td><td class="tal"> Do.  spore</td><td class="tar prl05 bl">33.</td><td class="tal">Puccinea, Mildew of corn</td></tr> -<tr><td class="tar pr05">12.</td><td class="tal">Sphærozosma</td><td class="tar prl05 bl">34.</td><td class="tal">Botrytis, mould on grapes</td></tr> -<tr><td class="tar pr05">13.</td><td class="tal">Chlorococcus</td><td class="tar prl05 bl"></td><td class="tal">  Do.  Sporules, beside it</td></tr> -<tr><td class="tar pr05">14.</td><td class="tal">Scenedesmus</td><td class="tar prl05 bl">35.</td><td class="tal">  Do.  parasitica, Potato blight</td></tr> -<tr><td class="tar pr05">15.</td><td class="tal">Pediastrum, to show cells</td><td class="tar prl05 bl">36.</td><td class="tal">Ectocarpus siliculosus</td></tr> -<tr><td class="tar pr05">16.</td><td class="tal">Ankistrodesmus</td><td class="tar prl05 bl">37.</td><td class="tal">Ulva latissima</td></tr> -<tr><td class="tar pr05">17.</td><td class="tal">Cosmarium</td><td class="tar prl05 bl">38.</td><td class="tal">Polypodium</td></tr> -<tr><td class="tar pr05">18.</td><td class="tal">Desmidium</td><td class="tar prl05 bl"></td><td class="tal">  Do.  single spore, below</td></tr> -<tr><td class="tar pr05">19.</td><td class="tal">Cosmarium, formation of Resting Spore </td><td class="tar prl05 bl">39.</td><td class="tal">Moss capsule, Hypnum</td></tr> -<tr><td class="tar pr05">20.</td><td class="tal">Cocconema lanceolatum</td><td class="tar prl05 bl">40.</td><td class="tal">Mare’s tail, Equisetum, <i>a</i></td></tr> -<tr><td class="tar pr05">21.</td><td class="tal">Diatoma vulgare</td><td class="tar prl05 bl"></td><td class="tal"> Do.  do.  <i>b</i> and <i>c</i></td></tr> -<tr><td class="tar pr05"></td><td class="tal">  Do.  larger frustules, at the side </td><td class="tar prl05 bl">41.</td><td class="tal">Porphyra laciniata</td></tr> -<tr><td class="tar pr05">22.</td><td class="tal">Volvox globator</td><td class="tar prl05 bl"></td><td class="tal"></td></tr> -</table></div> - -<div class="figcenter" style="width: 438px;"> -<a id="Pl_IV"></a> -<img src="images/i_p_004.jpg" width="438" height="700" alt="" /> -<div class="caption"><p>IV.</p></div> -</div> - -<p><span class="pagenum" title="81"><a name="Page_81" id="Page_81"></a></span></p> - -<p>On Fig. <a href="#Pl_IV">13</a> is delineated a very minute plant, -called from its colour Chlorococcus. It may be -found upon tree-trunks, walls, etc., in the form of -green dust, and has recently been found to take -part in forming the first stage of lichens.</p> - -<p>A large and interesting family of the “confervoid -algæ,” as these low forms of vegetable life are -termed, is the Desmidiaceæ, called in more common -parlance desmids. A few examples of this family -are given in Plate <a href="#Pl_IV">IV</a>.</p> - -<p>They may be found in water, always preferring -the cleanest and the brightest pools, mostly congregating -in masses of green film at the bottom of -the water, or investing the stems of plants. Their -removal is not very easy, but is best accomplished -by very carefully taking up this green slippery -substance in a spoon, and straining the water away -through fine muslin. They may also be separated -by allowing a ring, covered with muslin, to float -upon the surface of the water collected in a jar, -for, being great lovers of light, they assemble where -it is most abundant. An opaque jar should be -used. For preservation, glycerine-gelatine seems -to be the best fluid. A very full and accurate -description of these plants may be found in Ralfs’ -<i>British Desmidieæ</i>.</p> - -<p>Fig. <a href="#Pl_IV">4</a> represents one of the species of Closterium,<span class="pagenum" title="82"><a name="Page_82" id="Page_82"></a></span> -more than twenty of which are known. These -beautiful objects can be obtained from the bottom -of almost every clear pool, and are of some interest -on account of the circulating currents that may be -seen within the living plants. A high power is -required to see this phenomenon clearly. The -Closteria are reproduced in various ways. Mostly -they divide across the centre, being joined for a -while by two half-cells. Sometimes they reproduce -by means of conjugation, the process being -almost entirely conducted on the convex sides. -Fig. <a href="#Pl_IV">5</a> represents the end of a Closterium, much -magnified in order to show the actively moving -bodies contained within it.</p> - -<p>Fig. <a href="#Pl_IV">16</a> is a supposed desmid, called Ankistrodesmus, -and presumed to be an earlier stage of -Closterium.</p> - -<p>Fig. <a href="#Pl_IV">6</a> is a very pretty desmid called the -Pediastrum, and valuable to the microscopist as -exhibiting a curious mode of reproduction. The -figure shows a perfect plant composed of a number -of cells arranged systematically in a star-like shape; -Fig. <a href="#Pl_IV">15</a> is the same species without the colouring -matter, in order to show the shape of the cells. -The Pediastrum reproduces by continual subdivision -of the contents of each cell into a number of -smaller cells, termed “gonidia” on account of their -function on the perpetuation of the species. When -a sufficient number has been formed, they burst -through the envelope of the original cell, taking -with them a portion of its internal layer, so as to -form a vesicle, in which they move actively. In a<span class="pagenum" title="83"><a name="Page_83" id="Page_83"></a></span> -few minutes they arrange themselves in a circle, -and after a while they gradually assume the perfect -form, the whole process occupying about two days. -Fig. <a href="#Pl_IV">18</a> exhibits an example of the genus Desmidium. -In this genus the cells are either square -or triangular in their form, having two teeth at -their angles, and twisted regularly throughout their -length, causing the wavy or oblique lines which -distinguish them. The plants of this genus are -common, and may be found almost in any water. -I may as well mention that I have obtained nearly -all the preceding species, together with many others, -from a little pond on Blackheath.</p> - -<p>Fig. <a href="#Pl_IV">7</a> is another desmid called Scenedesmus, in -which the cells are arranged in rows of from two -to ten in number, the cell at each extremity being -often furnished with a pair of bristle-like appendages. -Fig. <a href="#Pl_IV">14</a> is another species of the same -plant, and both may be found in the water supplied -for drinking in London, as well as in any pond.</p> - -<p>A common species of desmid is seen at Fig. <a href="#Pl_IV">12</a>, -called Sphærozosma, looking much like a row of -stomata set chainwise together. It multiplies by -self-division.</p> - -<p>Fig. <a href="#Pl_IV">17</a> is a specimen of desmid named Cosmarium, -plentifully found in ponds on heaths and -commons, and having a very pretty appearance -in the microscope, with its glittering green centre -and beautifully transparent envelope. The manner -in which the Cosmarium conjugates is very remarkable, -and is shown at Fig. <a href="#Pl_IV">19</a>.</p> - -<p>The two conjugating cells become very deeply<span class="pagenum" title="84"><a name="Page_84" id="Page_84"></a></span> -cleft, and by degrees separate, suffering the contents -to pour out freely, and, as at present appears, without -any envelope to protect them. The mass, -however, soon acquires an envelope of its own, and -by degrees assumes a dark reddish-brown tint. It -is now termed a sporangium, and is covered with a -vast number of projections, which in this genus -are forked at their tip, but in others, which also -form sporangia, are simply pointed. The Closteria -conjugate after a somewhat similar manner, and it -is not unfrequent to find a pair in this condition, -but in their case the sporangium is quite smooth -on its surface.</p> - -<p>Another very remarkable family of confervoid -algæ is that which is known under the name of -Oscillatoriæ, from the oscillating movement of the -plant. They are always long and filamentous in -character, and may be seen moving up and down -with a curious irregularity of motion. Their -growth is extremely rapid, and may be watched -under a tolerably powerful lens, thus giving many -valuable hints as to the mode by which these -plants are reproduced. One of the commonest -species is represented at Fig. <a href="#Pl_IV">8</a>.</p> - -<p>Figs. 9, 10, and 11 are examples of another -family, called technically the Zygnemaceæ, because -they are so constantly yoked together by conjugation. -They all consist of a series of cylindrical -cells, set end to end, and having their green -contents arranged in similar patterns. Two of the -most common and typical species are here given.</p> - -<p>Fig. <a href="#Pl_IV">9</a> is the Spirogyra, so called from the<span class="pagenum" title="85"><a name="Page_85" id="Page_85"></a></span> -spiral arrangement of the chlorophyll; and Fig. <a href="#Pl_IV">10</a> -is the Tyndaridea, or Zygnema, as it is called by -some writers. A casual inspection will show how -easy it is to distinguish the one from the other. -Fig. <a href="#Pl_IV">11</a> represents a portion of the Tyndaridea -during the process of conjugation, showing the tube -of connection between the cells and one of the -spores.</p> - -<p class="mt2em">We now arrive at the diatoms, so called because -of their method of reproduction, in which it appears -as if a cut were made right along the original cell. -The commonest of these plants is the Diatóma -vulgáre, seen in Fig. <a href="#Pl_IV">21</a> as it appears while growing. -The reproduction of this plant is effected by splitting -down the centre, each half increasing to the -full size of the original cell; and in almost every -specimen of water taken from a pond, examples of -this diatom undergoing the process of division will -be distinguished. It also grows by conjugation. -The diatoms are remarkable for the delicate shell -or flinty matter which forms the cell skeleton, and -which will retain its shape even after intense heat -and the action of nitric acid. While the diatoms -are alive, swimming through the water, their -beautiful markings are clearly distinct, glittering -as if the form were spun from crystalline glass. -Just above the figure, and to the right hand, are -two outlines of single cells of this diatom, the -one showing the front view and the other the -profile.</p> - -<p>Fig. <a href="#Pl_IV">20</a> is an example of a diatom—Cocconéma<span class="pagenum" title="86"><a name="Page_86" id="Page_86"></a></span> -lanceolátum—furnished with a stalk. The left-hand -branch sustains a “frustule” exhibiting the -front view, while the other is seen sideways.</p> - -<p>Another common diatom is shown in Fig. <a href="#Pl_IV">23</a>, -and is known by the name of Synedra. This -constitutes a very large genus, containing about -seventy known species. In this genus the frustules -are at first arranged upon a sort of cushion, but in -course of time they mostly break away from their -attachment. In some species they radiate in every -direction from the cushion, like the spikes of the -ancient cavalier’s mace.</p> - -<p>Fig. <a href="#Pl_IV">24</a> is another stalked diatom called Gomphonéma -acuminátum, found commonly in ponds and -ditches. There are nearly forty species belonging -to this genus. A pair of frustules are also shown -which exhibit the beautiful flinty outline without -the coloured contents (technically called endochrome).</p> - -<p>Fig. <a href="#Pl_IV">27</a> is a side view of a beautiful diatom, -called Eunótia diadéma from its diadem-like form. -There are many species of this genus. When seen -upon the upper surface, it looks at first sight like a -mere row of cells with a band running along them; -but by careful arrangement of the light its true -form may easily be made out.</p> - -<p>Fig. <a href="#Pl_IV">28</a> represents a very common fresh-water -diatom, named Melosíra várians. The plants of -this genus look like a cylindrical rod composed of -a variable number of segments, mostly cylindrical, -but sometimes disc-shaped or rounded. An end -view of one of the frustules is seen at the left hand,<span class="pagenum" title="87"><a name="Page_87" id="Page_87"></a></span> -still coloured with its dots of “endochrome,” and -showing the cylindrical shape. Immediately above -is a figure of another frustule seen under both -aspects with the endochrome removed.</p> - -<p>A rather curious species of diatom, called Cocconeïs -pedículus, is seen at Fig. <a href="#Pl_IV">29</a> as it appears -on the surface of common water-cress. Sometimes -the frustules, which in all cases are single, are -crowded very closely upon each other and almost -wholly hide the substance on which they repose. -Fig. <a href="#Pl_IV">30</a> is another diatom of a flag-like shape, -named Achnanthes, having a long slender filament -attached to one end of the lower frustule, representing -the flag-staff. There are many wonderful -species of such diatoms, some running almost end -to end like a bundle of sticks, and therefore called -Bacillária; others spreading out like a number of -fans, such as the genus Licmophora; while some -assume a beautiful wheel-like aspect, of which the -genus Meridion affords an excellent example.</p> - -<p>A very remarkable, and not uncommon, fresh-water -diatom is the Bacillária paradóxa. It -looks, when at rest, like a broad brown ribbon of -varying length. The diatoms lie across the ribbon, -on edge, and slide upon each other exactly like the -ladders of a fire-escape, so that the broad ribbon is -converted into a fine long thread, which speedily -closes up again into the original ribbon, and so <i>da -capo</i>. The reason for this movement, and how it -is effected, is absolutely unknown; indeed, nothing -certain is known as to the way in which diatoms -move, nor has ever a probable guess yet been made.</p> - -<p><span class="pagenum" title="88"><a name="Page_88" id="Page_88"></a></span></p> - -<p>The last of the diatoms which we shall be able -to mention in this work is that represented on -Fig. <a href="#Pl_IV">31</a>. The members of this genus have the -name of Navícula, on account of their boat-like -shape and their habit of gliding through the water -in a canoe-like fashion. There are many species of -this genus, all of which are notable for the graceful -and varied courses formed by their outlines, and -the extreme delicacy of their markings. In many -species the markings are so extremely minute that -they can only be made out with the highest powers -of the microscope and the most careful illumination, -so that they serve as test objects whereby the performance -of a microscope can be judged by a -practical man.</p> - -<p class="mt2em">The large spherical figure in the centre of Plate <a href="#Pl_IV">IV</a>. -represents an example of a family belonging to -the confervoid algæ, and known by the name of -Volvox globator. There seems to be but one -species known.</p> - -<p>This singular plant has been greatly bandied -about between the vegetable and animal kingdoms, -but seems now to be satisfactorily settled -among the vegetables. In the summer it may be -found in pools of water, sufficiently large to be -visible to the naked eye, like a little green speck -proceeding slowly through the water. When a -moderate power is used, it appears as shown in -the figure, and always contains within its body a -number of smaller individuals, which after a while -burst through the envelope of the parent and start<span class="pagenum" title="89"><a name="Page_89" id="Page_89"></a></span> -upon an independent existence. On a closer examination, -a further generation may be discovered -even within the bodies of the children. The whole -surface is profusely covered with little green bodies, -each being furnished with a pair of movable cilia, -by means of which the whole organism is moved -through the water. These bodies are analogous to -the zoospores already mentioned, and are connected -with each other by a network of filaments. Reproduction -also takes place by conjugation as in -other algæ. A more magnified representation of -one of the green bodies is shown immediately above -the larger figure. The volvox is apt to die soon -when confined in a bottle.</p> - -<p>Fig. <a href="#Pl_IV">25</a> is the common yeast-plant, consisting -simply of a chain of cells, which increase by -budding, and only form spores when they have -exhausted the nutriment in the fluid in which they -live. Fig. <a href="#Pl_IV">26</a> is a curious object, whose scientific -name is Sárcina ventrículi. It is found in the -human stomach. Similar forms are often to be -found in the air; for instance, a piece of cocoa-nut -will exhibit this, and many other kinds of Bacteria -and moulds, after a few days’ exposure to the air, -preferably in a dark cupboard.</p> - -<p>We now come upon a few of the blights and -mildews. A very interesting series of forms is -first to be alluded to. Upon the bramble-leaf may -often be found spots, at first red, then orange, -then reddish black. These are known as Œcidium -berberidis. Fig. <a href="#Pl_IV">32</a> shows the “red-rust” of -wheat, the Urédo; and Fig. <a href="#Pl_IV">33</a> is the mildew of<span class="pagenum" title="90"><a name="Page_90" id="Page_90"></a></span> -corn, known as Puccinia. The interest lies in the -fact that these three forms are successive stages in -the life-history of the same plant. Another species -of Urédo, together with a Phragmídium, once -thought to be another kind of fungus, is seen on -a rose-leaf on Plate V. Fig. <a href="#Pl_V">1</a>. On Fig. <a href="#Pl_V">10</a>, -however, of the same Plate, the Phragmídium may -be seen proceeding from Urédo, thus proving them -to be but two states of the same plant. There is -room for any amount of observation and work in -connection with the life-histories of many of these -fungi.</p> - -<p>Another species of Puccinia, found on the thistle, -is shown on Plate V. Fig. <a href="#Pl_V">7</a>. Fig. <a href="#Pl_IV">34</a> is the mould -found upon decaying grapes, and called therefrom, -or from the clustered spores, Botrýtis. Some of -the detached spores are seen by its side. Fig. <a href="#Pl_IV">35</a> -is another species of the same genus, termed -Botrýtis parasítica, and is the cause of the well-known -“potato-disease.”</p> - -<p>The mosses and ferns afford an endless variety -of interesting objects to the microscopist; but as -their numbers are so vast, and the details of their -structure so elaborate, they can only be casually -noticed in the present work. Fig. <a href="#Pl_IV">38</a> represents -a spore-case of the Polypodium, one of the ferns, -as it appears while in the act of bursting and -scattering the contents around. One of the spores -is seen more magnified below. The spore-cases of -many ferns may be seen bursting under the microscope, -and have a very curious appearance, writhing -and twisting like worms, and then suddenly filling<span class="pagenum" title="91"><a name="Page_91" id="Page_91"></a></span> -the field with a cloud of spores. Fig. <a href="#Pl_V">9</a>, Plate V., -is a piece of the brown, chaff-like, scaly structure -found at the base of the stalk of male fern cells, -showing the manner in which a flat membrane is -formed. Fig. <a href="#Pl_IV">39</a> is a capsule of the Hypnum, one -of the mosses, showing the beautiful double fringe -with which its edge is crowned. Fig. <a href="#Pl_V">2</a>, Plate V., -is the capsule of another moss, Polytríchum, to -show the toothed rim; on the right hand is one -of the teeth much more magnified.</p> - -<p>Fig. <a href="#Pl_V">3</a>, Plate V., is the capsule of the Jungermannia, -one of the liverworts, showing the -“elaters” bursting out on every side, and scattering -the spores. Fig. <a href="#Pl_V">4</a> is a single elater much -magnified, showing it to be a spirally coiled -filament, that, by sudden expansion, shoots out -the spores just as a child’s toy-gun discharges the -arrow. Fig. <a href="#Pl_V">5</a> is a part of the leaf of the Sphagnum -moss, common in fresh water, showing the -curious spiral arrangement of secondary fibre -which is found in the cells, as well as the circular -pores which are found in each cell at a certain -stage of growth. Just below, and to the left hand, -is a single cell greatly magnified, in order to show -these peculiarities more strongly. Fig. <a href="#Pl_V">8</a> is part -of a leaf of Jungermannia, showing the dotted -cells.</p> - -<p>Fig. <a href="#Pl_V">6</a>, Plate V., is a part of a rootlet of moss, -showing how it is formed of cells elongated and -joined end to end.</p> - -<p>On the common mare’s-tail, or Equisétum, may -be seen a very remarkable arrangement for scattering<span class="pagenum" title="92"><a name="Page_92" id="Page_92"></a></span> -the spores. On the last joint of the stem is -a process called a fruit-spike, being a pointed head -around which are set a number of little bodies just -like garden-tables, with their tops outward. One -of these bodies is seen in Fig. <a href="#Pl_IV">40</a>. From the top -of the table depend a number of tiny pouches, -which are called sporangia; these lie closely against -each other, and contain the spores. At the proper -moment these pouches burst from the inside, and -fling out the spores, which then look like round -balls with irregular surfaces, as shown in Fig. <a href="#Pl_IV">40</a>, <i>c</i>. -This irregularity is caused by four elastic filaments, -knobbed at the end, which are originally coiled -tightly round the body of the spore, but by rapidly -untwisting themselves cause the spore to leap -about, and so aid in the distribution. A spore -with uncoiled filaments is seen at Fig. <a href="#Pl_IV">40</a>, <i>b</i>. By -breathing on them they may be made to repeat -this process at will.</p> - -<p>Fig. <a href="#Pl_IV">36</a> is a common little sea-weed, called -Ectocarpus siliculósus, that is found parasitically -adhering to large plants, and is figured in order -to show the manner in which the extremities of -the branches are developed into sporangia. Fig. <a href="#Pl_IV">37</a> -is a piece of the common green laver, Ulva latíssima, -showing the green masses that are ultimately -converted into zoospores, and by their extraordinary -fertility cause the plant to grow with such rapid -luxuriance wherever the conditions are favourable. -Every possessor of a marine aquarium knows how -rapidly the glass sides become covered with growing -masses of this plant. The smaller figure above is a<span class="pagenum" title="93"><a name="Page_93" id="Page_93"></a></span> -section of the same plant, showing that it is composed -of a double plate of cellular tissue.</p> - -<p>Fig. <a href="#Pl_IV">41</a> is a piece of purple laver or “sloke,” -Porphýra laciniáta, to show the manner in which -the cells are arranged in groups of four, technically -named “tetraspores.” This plant has only one -layer of cells.</p> - -<p>On Plate V. may be seen a number of curious -details of the higher algæ.</p> - -<p>Fig. <a href="#Pl_V">11</a> is the Sphacelária, so called from the -curious capsule cells found at the end of the -branches, and termed sphacelæ. This portion of -the plant is shown more magnified in Fig. <a href="#Pl_V">12</a>. -Another sea-weed is represented in Fig. <a href="#Pl_V">13</a>, in -order to show the manner in which the fruit is -arranged; and a portion of the same plant is given -on a larger scale at Fig. <a href="#Pl_V">14</a>.</p> - -<p>A very pretty little sea-weed called Cerámium -is shown at Fig. <a href="#Pl_V">15</a>; and a portion showing the -fruit much more magnified is drawn at Fig. <a href="#Pl_V">22</a>. -Fig. <a href="#Pl_V">23</a> is a little alga called Myrionéma, growing -parasitically on the preceding plant.</p> - -<p>Fig. <a href="#Pl_V">16</a> is a section of a capsule belonging to the -Hálydris siliquósa, showing the manner in which -the fruit is arranged; and Fig. <a href="#Pl_V">17</a> shows one of -the spores more magnified.</p> - -<p>Fig. <a href="#Pl_V">18</a> shows the Polysiphónia parasítica, a -rather common species of a very extensive genus of -sea-weeds, containing nearly three hundred species. -Fig. <a href="#Pl_V">19</a> is a portion of the stem of the same plant, -cut across in order to show the curious mode in -which it is built up of a number of longitudinal<span class="pagenum" title="94"><a name="Page_94" id="Page_94"></a></span> -cells, surrounding a central cell of large dimensions, -so that a section of this plant has the aspect of a -rosette when placed under the microscope. A -capsule or “ceramídium” of the same plant is -shown at Fig. <a href="#Pl_V">20</a>, for the purpose of exhibiting -the pear-shaped spores, and the mode of their -escape from the parent-cell previous to their own -development into fresh plants. The same plant -has another form of reproduction, shown in Fig. <a href="#Pl_V">21</a>, -where the “tetraspores” are seen imbedded in the -substance of the branches. There is yet a third -mode of reproduction by means of “antheridia,” or -elongated white tufts at the extremities of the -branches. The cells produced by these tufts -fertilise the rudimentary capsules, and so fulfil -the function of the pollen in flowering plants.</p> - -<p>Fig. <a href="#Pl_V">25</a> is the Cladóphora, a green alga, figured -to illustrate its mode of growth; and Fig. <a href="#Pl_V">26</a> -represents one of the red sea-weeds, Ptilóta élegans, -beautifully feathered, and with a small portion shown -also on a larger scale, in order to show its structure -more fully. A good contrast to this species is seen -on Fig. <a href="#Pl_V">27</a>, and the mode in which the long, slender, -filamentary fronds are built up of many-sided cells -is seen just to the left hand of the upper frond. -Fig. <a href="#Pl_V">24</a> is a portion of the lovely Delesséria sanguínea, -given in order to show the formation of -the cells, as also the arrangement by which the -indistinct nervures are formed.</p> - - -<p class="tac">V.</p> - -<div class="center"> -<table border="0" cellpadding="0" cellspacing="0" summary="Key to Plate V"> -<tr><td class="tar pr05 fs70">FIG.</td></tr> -<tr><td class="tar pr05">1.</td><td class="tal">Rose Leaf, with fungus</td><td class="tar prl05 bl">15.</td><td class="tal">Ceramium</td></tr> -<tr><td class="tar pr05">2.</td><td class="tal">Moss capsule, Polytrichum</td><td class="tar prl05 bl">16.</td><td class="tal">Capsule, Halidrys</td></tr> -<tr><td class="tar pr05">3.</td><td class="tal">Jungermannia, capsule</td><td class="tar prl05 bl">17.</td><td class="tal">Spore of do.</td></tr> -<tr><td class="tar pr05">4.</td><td class="tal"> Do.  an elater more magnified </td><td class="tar prl05 bl">18.</td><td class="tal">Polysiphonia parasitica</td></tr> -<tr><td class="tar pr05">5.</td><td class="tal">Leaf of Moss, Sphagnum</td><td class="tar prl05 bl">19.</td><td class="tal"> Do.  stem, more magnified</td></tr> -<tr><td class="tar pr05">6.</td><td class="tal">Rootlet, Moss</td><td class="tar prl05 bl">20.</td><td class="tal"> Do.  Capsule, tetraspores escaping</td></tr> -<tr><td class="tar pr05">7.</td><td class="tal">Puccinia, from Thistle</td><td class="tar prl05 bl">21.</td><td class="tal"> Do.  fruit, another form</td></tr> -<tr><td class="tar pr05">8.</td><td class="tal">Jungermannia, leaf</td><td class="tar prl05 bl">22.</td><td class="tal">Ceramium, fruit</td></tr> -<tr><td class="tar pr05">9.</td><td class="tal">Scale from stalk of male fern </td><td class="tar prl05 bl">23.</td><td class="tal">Myrionema, parasitic Seaweed</td></tr> -<tr><td class="tar pr05">10.</td><td class="tal">Uredo</td><td class="tar prl05 bl">24.</td><td class="tal">Delesseria sanguinea, Frond</td></tr> -<tr><td class="tar pr05">11.</td><td class="tal">Sphacelaria filicina</td><td class="tar prl05 bl">25.</td><td class="tal">Cladophora</td></tr> -<tr><td class="tar pr05">12.</td><td class="tal"> Do.  top, more magnified </td><td class="tar prl05 bl">26.</td><td class="tal">Ptilota elegans</td></tr> -<tr><td class="tar pr05">13.</td><td class="tal">Seaweed, showing fruit</td><td class="tar prl05 bl">27.</td><td class="tal">Enteromorpha clathrata</td></tr> -<tr><td class="tar pr05">14.</td><td class="tal"> Do.  fruit, more magnified</td><td class="tar prl05 bl">28.</td><td class="tal">Nitophyllum laceratum</td></tr> -</table></div> - -<div class="figcenter" style="width: 435px;"> -<a id="Pl_V"></a> -<img src="images/i_p_005.jpg" width="435" height="700" alt="" /> -<div class="caption"><p>V.</p></div> -</div> - -<p><span class="pagenum" title="95"><a name="Page_95" id="Page_95"></a></span></p> - -<p>The figure on the bottom left-hand corner of -Plate V. is a portion of the pretty Nitophyllum -lacerátum, a plant belonging to the same family -as the preceding one. The specimen here represented -has a gathering of spores upon the frond, -in which state the frond is said to be “in fruit.”</p> - -<p>Fig. <a href="#Pl_V">27</a> represents a portion of the common sea-grass -(<i>Enteromorpha</i>), so common on rocks and -stones between the range of high and low water. -On the left hand of the figure, and near the top, -is a small piece of the same plant much more -magnified, in order to show the form of its cells.</p> - -<hr class="chap" /> - -<div class="chapter"> -<p><span class="pagenum" title="96"><a name="Page_96" id="Page_96"></a></span></p> - - - - -<h2>CHAPTER VII</h2> -</div> - -<p class="subhead">Antennæ, their Structure and Use—Eyes, Compound and -Simple—Breathing Organs—Jaws and their Appendages—Legs, -Feet, and Suckers—Digestive Organs—Wings, -Scales, and Hairs—Eggs of Insects—Hair, Wool, Linen, -Silk, and Cotton—Scales of Fish—Feathers—Skin and -its Structure—Epithelium—Nails, Bone, and Teeth—Blood -Corpuscles and Circulation—Elastic Tissues—Muscle -and Nerve.</p> - - -<p>We now take leave of the vegetables for a time, -and turn our attention to the animal kingdom.</p> - -<p>On Plate <a href="#Pl_VI">VI</a>. may be seen many beautiful -examples of animal structures, most of them -being taken from the insect tribes. We will -begin with the antennæ, or horns, as they are -popularly termed, of the insect.</p> - -<p>The forms of these organs are as varied as those -of the insects to which they belong, and they are -so well defined that a single antenna will, in -almost every instance, enable a good entomologist -to designate the genus to which the insect belonged. -The functions of the antennæ are not satisfactorily -ascertained. They are certainly often used as -organs of speech, as may be seen when two ants -meet each other, cross their antennæ, and then -start off simultaneously to some task which is too<span class="pagenum" title="97"><a name="Page_97" id="Page_97"></a></span> -much for a single ant. This pretty scene may be -witnessed on any fine day in a wood, and a very -animated series of conversations may readily be -elicited by laying a stick across their paths, or -putting a dead mouse or large insect in their -way.</p> - -<p>I once saw a very curious scene of this kind -take place at an ant’s nest near Hastings. A -great daddy long-legs had, unfortunately for itself, -settled on the nest, and was immediately “pinned” -by an ant or two at each leg, so effectually that -all its struggles availed nothing. Help was, however, -needed, and away ran four or five ants in -different directions, intercepting every comrade -they met, and by a touch of the antennæ sending -them off in the proper direction. A large number -of the wise insects soon crowded round the poor -victim, whose fate was rapidly sealed. Every ant -took its proper place, just like a gang of labourers -under the orders of their foreman; and by dint of -pushing and pulling, the long-legged insect was -dragged to one of the entrances of the nest, and -speedily disappeared.</p> - -<p>Many of the ichneumon-flies may also be seen -quivering their antennæ with eager zeal, and evidently -using them as feelers, to ascertain the -presence of the insect in which they intend to lay -their eggs; and many other similar instances will -be familiar to anyone who has been in the habit of -watching insects and their ways.</p> - -<p>It is, however, most likely that the antennæ -serve other purposes than that which has just<span class="pagenum" title="98"><a name="Page_98" id="Page_98"></a></span> -been mentioned, and many entomologists are of -opinion that they serve as organs of hearing.</p> - -<p>Fig. <a href="#Pl_VI">15</a>, Plate VI., represents a part of one of -the joints belonging to the antennæ of the common -house-fly; it is seen to be covered with a multitude -of little depressions, some being small, and -others very much larger. A section of the same -antenna, but on a larger scale, is shown by Fig. <a href="#Pl_VI">16</a>, -in order to exhibit the real form of these depressions. -Nerves have been traced to these curious -cavities, which evidently serve some very useful -purpose, some authors thinking them to belong to -the sense of smell, and others to that of hearing. -Perhaps they may be the avenues of some sensation -not possessed by the human race, and of which we -are therefore ignorant. Fig. <a href="#Pl_VI">17</a> represents a section -of the antennæ of an ichneumon-fly, to show -the structure of these organs of sense.</p> - -<p>We will now glance cursorily at the forms of -antennæ which are depicted in the Plate.</p> - -<p>Fig. <a href="#Pl_VI">1</a> is the antenna of the common cricket, -which consists of a vast number of little joints, -each a trifle smaller than the preceding one, the -whole forming a long, thread-like organ. Fig. <a href="#Pl_VI">2</a> is -taken from the grasshopper, and shows that the -joints are larger in the middle than at either end.</p> - -<p>Figs. <a href="#Pl_VI">3</a> and 5 are from two minute species of -cocktailed beetles (<i>Staphylínidæ</i>), which swarm -throughout the summer months, and even in the -winter may be found in profusion under stones -and moss. The insect from which Fig. <a href="#Pl_VI">5</a> was -taken is so small that it is almost invisible to the<span class="pagenum" title="99"><a name="Page_99" id="Page_99"></a></span> -naked eye, and was captured on the wing by -waving a sheet of gummed paper under the shade -of a tree. These are the tiresome little insects -that so often get into the eye in the summer, and -cause such pain and inconvenience until they are -removed.</p> - -<p>Fig. <a href="#Pl_VI">4</a> shows the antenna of the tortoise beetle -(<i>Cássida</i>), so common on many leaves, and remarkable -for its likeness to the reptile from which it -derives its popular name. Fig. <a href="#Pl_VI">3</a> is from one of -the weevils, and shows the extremely long basal -joint of the antennæ of these beetles, as well as -the clubbed extremity. Fig. <a href="#Pl_VI">7</a> is the beautifully -notched antenna of the cardinal beetle (<i>Pyrochróa</i>), -and Fig. <a href="#Pl_VI">11</a> is the fan-like one of the common -cockchafer. This specimen is taken from a male -insect, and the reader will find his trouble repaid -on mounting one of these antennæ as a permanent -object.</p> - -<p>Fig. <a href="#Pl_VI">12</a> is an antenna from one of the common -ground beetles (<i>Cárabus</i>) looking like a string of -elongated pears, from the form of the joints. The -reader will see that in beetles he is sure to find -eleven joints in the antennæ.</p> - -<p>Fig. <a href="#Pl_VI">10</a> is the entire antenna of a fly (<i>Syrphus</i>), -one of those pretty flies which may be seen hovering -over one spot for a minute, and then darting off -like lightning to hang over another. The large -joint is the one on which are found those curious -depressions that have already been mentioned. -Fig. <a href="#Pl_VI">8</a> is one of the antennæ of a tortoise-shell -butterfly (<i>Vanessa</i>), showing the slender, knobbed<span class="pagenum" title="100"><a name="Page_100" id="Page_100"></a></span> -form which butterfly antennæ assume; and Figs. <a href="#Pl_VI">13</a> -and 14 are specimens of moths’ antennæ, -showing how they always terminate in a point. -Fig. <a href="#Pl_VI">13</a> is the beautiful feathery antenna of the -ermine moth (<i>Spilosóma</i>); and Fig. <a href="#Pl_VI">14</a> is the -toothed one of the tiger moth (<i>Arctia caja</i>). In -all these feathered and toothed antennæ of moths, -the male insects have them much more developed -than the female, probably for the purpose of -enabling them to detect the presence of their -mates, a property which some possess in wonderful -perfection. The male oak-egger moth, for example, -can be obtained in any number by putting a female -into a box with a perforated lid, placing the box -in a room, and opening the window. In the course -of the evening seven or eight males are seen to -make their appearance, and they are so anxious to -get at their intended mate that they will suffer -themselves to be taken by hand.</p> - -<p>Fig. <a href="#Pl_VI">9</a> is an antenna of the male gnat, a most -beautiful object, remarkable for the delicate transparency -of the joints, and the exquisitely fine -feathering with which they are adorned.</p> - -<p>We now arrive at the eyes of the insects, all of -which are very beautiful, and many singularly full -of interest.</p> - -<p>In the centre of Plate <a href="#Pl_VI">VI</a>. may be seen the front -view of the head of a bee, showing both kinds of -eyes, three simple eyes arranged triangularly in the -centre, and two large masses, compound eyes, at the -sides.</p> - -<p>The simple eyes, termed “ocelli,” are from one<span class="pagenum" title="101"><a name="Page_101" id="Page_101"></a></span> -to three in number, and usually arranged in a -triangular form between the two compound eyes. -Externally they look merely like shining rounded -projections, and can be seen to great advantage in -the dragon-flies. The compound eyes may be -considered as aggregations of simple eyes, set -closely together, and each assuming a more or -less perfect six-sided form. Their number varies -very greatly; in some insects, such as the common -fly, there are about four thousand of these simple -eyes in one compound one, in the ant only fifty, -in the dragon-fly about twelve thousand, and in -one of the beetles more than twenty-five thousand.</p> - -<p>Fig. <a href="#Pl_VI">18</a> shows a portion of the compound eye of -the Atalanta butterfly, and Fig. <a href="#Pl_VI">20</a> the same organ -of the death’s-head moth. A number of the protecting -hairs may be seen still adhering to the eye -of the butterfly. Fig. <a href="#Pl_VI">22</a> is a remarkably good -specimen of the eye of a fly (<i>Helióphilus</i>), showing -the facets, nearly square, the tubes to which they -are attached, and portions of the optic nerves. -Fig. <a href="#Pl_VI">23</a> is part of the compound eye of a lobster, -showing the facets quite square. All these drawings -were taken by the camera lucida from my -own preparations, so that I can answer for their -authenticity.</p> - -<p>On Plate VIII. Figs. 6 and 12, the reader will -find two more examples of eyes, these being taken -from the spiders. Fig. <a href="#Pl_VIII">6</a> is an example of the -eight eyes of the well-known zebra spider, so -common on our garden walls and similar situations, -hunting incessantly after flies and other prey,<span class="pagenum" title="102"><a name="Page_102" id="Page_102"></a></span> -and capturing them by a sudden pounce. The -eyes are like the ocelli of insects, and are simple -in their construction. The number, arrangement, -and situation of the eyes is extremely varied in -spiders, and serves as one of the readiest modes of -distinguishing the species. Fig. <a href="#Pl_VIII">12</a>, Plate VIII., -represents one of the curious eyes of the common -harvest spider, perched on a prominence or -“watch-tower” (as it has been aptly named), for -the purpose of enabling the creature to take a more -comprehensive view of surrounding objects.</p> - -<p class="mt2em">Returning to Plate VI., in Fig. <a href="#Pl_VI">21</a> we see a -curiously branched appearance, something like the -hollow root of a tree, and covered with delicate -spiral markings. This is part of the breathing -apparatus of the silkworm, extracted and prepared -by myself for the purpose of showing the manner -in which the tubes branch off from the “spiracle” -or external breathing-hole, a row of which may be -seen along the sides of insects, together with the -beautiful spiral filament which is wound round -each tube for the purpose of strengthening it. One -of these spiracles may be seen in the neck of the -gnat (Fig. <a href="#Pl_VI">27</a>). Another spiracle, more enlarged, -may be seen on Plate VII. Fig. <a href="#Pl_VII">34</a>, taken from -the wireworm, <i>i.e.</i> the larva of the skipjack beetle -(<i>Eláter</i>), to show the apparatus for excluding dust -and admitting air. The object of the spiral coil is -very evident, for as these breathing-tubes extend -throughout the whole body and limbs, they would -fail to perform their office when the limbs were<span class="pagenum" title="103"><a name="Page_103" id="Page_103"></a></span> -bent, unless for some especial provision. This is -achieved by the winding of a very strong but -slender filament between the membranes of which -the tube is composed, so that it always remains -open for the passage of air throughout all the -bends to which it may be subjected. Flexible -tubes for gas and similar purposes are made after -the same fashion, spiral metal wire being coiled -within the india-rubber pipe. A little piece of -this thread is seen unwound at the end of a small -branch towards the top, and this thread is so strong -that it retains its elasticity when pulled away from -the tube, and springs back into its spiral form. -I have succeeded in unwinding a considerable -length of this filament from the breathing-tube of a -humble bee.</p> - -<p>Fig. <a href="#Pl_VI">28</a> represents the two curious tubercles upon -the hinder quarters of the common green-blight, -or Aphis, so very common on our garden plants, as -well as on many trees and other vegetables. From -the tips of these tubercles exudes a sweet colourless -fluid, which, after it has fallen upon the leaves, is -popularly known by the name of honey-dew. Ants -are very fond of this substance, and are in the -habit of haunting the trees upon which the aphides -live, for the purpose of sucking the honey-dew as -it exudes from their bodies. A drop of this liquid -may be seen on the extremity of the lower tubercle.</p> - -<p>The head of the same insect may be seen in Fig. <a href="#Pl_VI">24</a>, -where the reader may observe the bright scarlet -eye, and the long beak with which the aphis -punctures the leaves and sucks the sap. <span class="pagenum" title="104"><a name="Page_104" id="Page_104"></a></span>Fig. <a href="#Pl_VI">29</a> -is the head of the sheep-tick, exhibiting the organ -by which it pierces the skin of the creature on -which it lives. Fig. <a href="#Pl_VI">25</a> is the head of another -curious parasite found upon the tortoise, and -remarkable for the powerful hooked apparatus -which projects in front of the head.</p> - -<p>Turning to Plate VII. Fig. <a href="#Pl_VII">4</a>, we find the head -of a ground beetle (<i>Cárabus</i>), valuable as exhibiting -the whole of the organs of the head and mouth.</p> - -<p>Immediately above the compound eyes are seen -the roots of the antennæ, those organs themselves -being cut away. Above there are two pairs of -similarly constructed organs termed the “maxillary -palpi,” because they belong to the lesser jaws or -maxillæ, seen just within the pair of great curved -jaws called the mandibles, which are extended in so -threatening a manner. The “labial palpi,” so called -because they belong to the “labium,” or under lip, -are seen just within the others; the tongue is seen -between the maxillæ, and the chin or “mentum” -forms a defence for the base of the maxillæ and -the palpi. A careful examination of a beetle’s -mouth with the aid of a pocket lens is very instructive -as well as interesting.</p> - -<p>Fig. <a href="#Pl_VII">1</a> on the same Plate shows the jaws of the -hive bee, where the same organs are seen modified -into many curious shapes. In the centre may be -seen the tongue, elongated into a flexible and hair-covered -instrument, used for licking the honey -from the interior of flowers. At each side of the -tongue are the labial palpi, having their outermost -joints very small, and the others extremely large, -the latter acting as a kind of sheath for the tongue. -Outside the labial palpi are the maxillæ, separated -in the specimen, but capable of being laid closely -upon each other, and outside all are the mandibles.</p> - - -<p class="tac">VI.</p> - -<div class="center"> -<table border="0" cellpadding="0" cellspacing="0" summary="Key to Plate VI"> -<tr><td class="tar pr05 fs70">FIG.</td></tr> -<tr><td class="tar pr05">1.</td><td class="tal">Antenna, Cricket</td><td class="tar prl05 bl">16.</td><td class="tal"> Do.  do. section</td></tr> -<tr><td class="tar pr05">2.</td><td class="tal"> Do.  Grasshopper</td><td class="tar prl05 bl">17.</td><td class="tal"> Do.  Ichneumon</td></tr> -<tr><td class="tar pr05">3.</td><td class="tal"> Do.  Staphylinus</td><td class="tar prl05 bl">18.</td><td class="tal">Eye of Butterfly, Atalanta</td></tr> -<tr><td class="tar pr05">4.</td><td class="tal"> Do.  Cassida</td><td class="tar prl05 bl">19.</td><td class="tal">Eyes, Bee</td></tr> -<tr><td class="tar pr05">5.</td><td class="tal"> Do.  Staphylinus</td><td class="tar prl05 bl">20.</td><td class="tal">Eye, Death’s Head Moth</td></tr> -<tr><td class="tar pr05">6.</td><td class="tal"> Do.  Weevil</td><td class="tar prl05 bl">21.</td><td class="tal">Breathing-tube, Silkworm</td></tr> -<tr><td class="tar pr05">7.</td><td class="tal"> Do.  Pyrochroa</td><td class="tar prl05 bl">22.</td><td class="tal">Eye, Heliophilus</td></tr> -<tr><td class="tar pr05">8.</td><td class="tal"> Do.  Butterfly, Tortoiseshell </td><td class="tar prl05 bl">23.</td><td class="tal"> Do.  Lobster</td></tr> -<tr><td class="tar pr05">9.</td><td class="tal"> Do.  Gnat, male</td><td class="tar prl05 bl">24.</td><td class="tal"> Do.  Aphis of Geranium</td></tr> -<tr><td class="tar pr05">10.</td><td class="tal"> Do.  Syrphus</td><td class="tar prl05 bl">25.</td><td class="tal">Head, Parasite of Tortoise</td></tr> -<tr><td class="tar pr05">11.</td><td class="tal"> Do.  Cockchafer, male </td><td class="tar prl05 bl">26.</td><td class="tal">Hind leg, Aphis of Geranium</td></tr> -<tr><td class="tar pr05">12.</td><td class="tal"> Do.  Ground Beetle</td><td class="tar prl05 bl">27.</td><td class="tal">Head, Gnat</td></tr> -<tr><td class="tar pr05">13.</td><td class="tal"> Do.  Ermine Moth</td><td class="tar prl05 bl">28.</td><td class="tal">“Paps” of Aphis</td></tr> -<tr><td class="tar pr05">14.</td><td class="tal"> Do.  Tiger Moth</td><td class="tar prl05 bl">29.</td><td class="tal">Head, Sheep-tick</td></tr> -<tr><td class="tar pr05">15.</td><td class="tal"> Do.  Blowfly</td><td class="tar prl05 bl">30.</td><td class="tal">Foot, Tipula</td></tr> -</table></div> - -<div class="figcenter" style="width: 436px;"> -<a id="Pl_VI"></a> -<img src="images/i_p_006.jpg" width="436" height="700" alt="" /> -<div class="caption"><p>VI.</p></div> -</div> - -<p><span class="pagenum" title="105"><a name="Page_105" id="Page_105"></a></span></p> - -<p>The curiously elongated head of the scorpion-fly -(<i>Panorpa</i>), seen at Fig. <a href="#Pl_VII">7</a>, affords another example -of the remarkable manner in which these organs -are developed in different insects. Another -elongated head, belonging to the daddy long-legs, -is seen in Plate VI. Fig. <a href="#Pl_VI">27</a>, and well shows -the compound eyes, the antennæ, and the palpi. -Fig. <a href="#Pl_VII">2</a> represents the coiled tongue of the Atalanta -butterfly; it is composed of the maxillæ, very -greatly developed, and appearing as if each had -originally been flat, and then rolled up so as to -make about three-fourths of a tube. A number of -projections are seen towards the tip, and one of -these little bodies is shown on a larger scale at -Fig. <a href="#Pl_VII">3</a>. These curious organs have probably some -connection with the sense of taste. Along the -edges of the semi-tubes are arranged a number of -very tiny hooks, by means of which the insect can -unite the edges at will.</p> - -<p>Fig. <a href="#Pl_VII">11</a>, in the centre of the Plate, shows one of -the most curious examples of insect structure, the -proboscis or trunk of the common bluebottle-fly. -The maxillary palpi covered with bristles are seen -projecting at each side, and upon the centre are -three lancet-like appendages, two small and one -large, which are used for perforating various -substances on which the insect feeds. The great -double disc at the end is composed of the lower lip<span class="pagenum" title="106"><a name="Page_106" id="Page_106"></a></span> -greatly developed, and is filled with a most complex -arrangement of sucking-tubes, in order to enable -it to fulfil its proper functions. The numerous -tubes which radiate towards the circumference are -strengthened by a vast number of partial rings of -strong filamentary substance, like that which we -have already seen in the breathing-tube of the -silkworm. Some of these partial rings are seen on -Fig. <a href="#Pl_VII">12</a>, a little above. The mode in which the -horny matter composing the rings is arranged -upon the tubes is most wonderful, and requires a -tolerably high power to show it. The fine hairs -upon the proboscis itself afford most admirable -practice for the young microscopist. They should, -when properly lighted and focused, be quite black -and sharp. Any errors of manipulation will cause -them to be “fuzzy.”</p> - -<p>Fig. <a href="#Pl_VII">5</a> shows the tongue of the common cricket, -a most elegantly formed organ, having a number of -radiating bands covered with zigzag lines, due to -the triangular plates of strengthening substance -with which they are furnished, instead of the rings. -A portion more highly magnified is shown at -Fig. <a href="#Pl_VII">6</a>, exhibiting the manner in which the -branches are arranged.</p> - -<p class="mt2em">The legs of insects now claim our attention.</p> - -<p>Fig. <a href="#Pl_VII">9</a>, Plate VII., shows the “pro-leg” of a -caterpillar. The pro-legs are situated on the -hinder parts of the caterpillar, and, being set in -pairs, take a wonderfully firm hold of a branch or -twig by pressure toward each other. Around the<span class="pagenum" title="107"><a name="Page_107" id="Page_107"></a></span> -pro-legs are arranged a series of sharp hooks, set -with their points inwards, for greater power in -holding. Fig. <a href="#Pl_VII">10</a> represents one of the hooks more -magnified.</p> - -<p>Fig. <a href="#Pl_VII">15</a> is the lower portion of the many-jointed -legs of the long-legged spider (<i>Phalángium</i>), the -whole structure looking very like the antenna of -the cricket. Fig. <a href="#Pl_VII">17</a> is the leg of the glow-worm, -showing the single claw with which it is armed. -Fig. <a href="#Pl_VII">26</a> shows the foot of the flea, furnished with -two simple claws. Fig. <a href="#Pl_VII">16</a> is the foot of the -Trombídium, a genus of parasitic creatures, to -which the well-known harvest-bug belongs. Fig. <a href="#Pl_VI">26</a>, -Plate VI., shows the leg of the green Aphis of -the geranium, exhibiting the double claw, and the -pad or cushion, which probably serves the same -purpose as the pads found upon the feet of many -other insects. Fig. <a href="#Pl_VII">8</a> is the lower portion of the -leg of the ant, showing the two claws and the -curious pad in the centre, by means of which the -insect is able to walk upon slippery surfaces. The -Típula has a foot also furnished with a single pad -(see Plate VI. Fig. <a href="#Pl_VI">30</a>). This organ is seen under -a very high power to be covered with long hair-like -appendages, each having a little disc at the -end, and probably secreting some glutinous fluid -which will enable the creature to hold on to -perpendicular and smooth surfaces. Many of my -readers will doubtless have noticed the common -fly, towards the end of autumn, walking stiffly -upon the walls, and evidently detaching each foot -with great difficulty, age and infirmity having made<span class="pagenum" title="108"><a name="Page_108" id="Page_108"></a></span> -the insect unable to lift its feet with the requisite -force.</p> - -<p>Fig. <a href="#Pl_VII">21</a> is the foot of one of the ichneumon-flies -(<i>Ophíon</i>), the hairy fringe being apparently for the -purpose of enabling it to hold firmly to the caterpillar -in which it is depositing its eggs, and which -wriggles so violently under the infliction that it -would soon throw its tormentor had not some -special means been provided for the purpose of -enabling the latter to keep its hold. Fig. <a href="#Pl_VII">20</a> is -a beautiful example of a padded foot, taken from -the little red parasitic creature so plentifully found -upon the dor or dung beetle (<i>Geotrúpes</i>), and of -which the afflicted insect is said to rid itself by -lying on its back near an ant’s nest, and waiting -until the ants carry off its tormentors.</p> - -<p>Fig. <a href="#Pl_VII">18</a> is the foot of the common yellow dung-fly -(plentiful in pasture lands), having two claws -and two pads; and Fig. <a href="#Pl_VII">19</a> shows the three pads -and two claws found in the foot of the hornet-fly -(<i>Ásilus</i>).</p> - -<p>Few microscopic objects call forth such general -and deserved admiration as the fore-foot of the -male water-beetle (<i>Dytiscus</i>), when properly prepared -and mounted, for which see Fig. <a href="#Pl_VII">13</a>.</p> - -<p>On examining this preparation under the microscope, -it is seen that three of the joints are greatly -expanded, and that the whole of their under -surface is covered profusely with certain wonderful -projections, which are known to act as suckers. -One of them is exceedingly large, and occupies -a very considerable space, its hairs radiating like<span class="pagenum" title="109"><a name="Page_109" id="Page_109"></a></span> -the rays of the heraldic sun. Another is also -large, but scarcely half the diameter of the former, -and the remainder are small, and mounted on the -extremities of delicate foot-stalks, looking something -like wide-mouthed trumpets. In the specimen -from which the drawing was taken the smaller -suckers are well shown, as they protrude from the -margin of the foot.</p> - -<p>One of the larger suckers is seen more magnified -on Fig. <a href="#Pl_VII">14</a>.</p> - -<p>Plate VIII. Fig. <a href="#Pl_VIII">1</a>, exemplifies the manner -in which the muscles of insects do their work, -being well attached in the limbs to the central -tendon, and pulling “with a will” in one direction, -thus giving very great strength. This leg is taken -from the water boatman (<i>Notonecta</i>), and has been -mounted in Canada balsam.</p> - -<p>On Plate VII. Fig. <a href="#Pl_VII">29</a>, may be seen a curiously -formed creature. This is the larva of the tortoise -beetle (<i>Cássida</i>), the skin having been flattened -and mounted in Canada balsam. The spiracles are -visible along the sides, and at the end is seen a -dark fork-like structure. This is one of the -peculiarities of this creature, and is employed for -the purpose of carrying the refuse of its food, -which is always piled upon its back, and retained -in its place by the forked spines, aided probably -by the numerous smaller spines that project from -the side.</p> - -<p>Fig. <a href="#Pl_VII">33</a> shows part of the stomach and gastric -teeth of the grasshopper. This structure may be -seen to perfection in the “gizzard,” as it is called,<span class="pagenum" title="110"><a name="Page_110" id="Page_110"></a></span> -of the great green locust of England (<i>Ácrida -viridíssima</i>). The organ looks like a sudden swelling -of the œsophagus, and when slit longitudinally -under water, the teeth may be seen in rows set -side by side, and evidently having a great grinding -power. The common house cricket has a similar -organ of remarkable beauty. Just above (Fig. <a href="#Pl_VII">27</a>) -is the corresponding structure in the hive bee, -three of the teeth being shown separately at -Fig. <a href="#Pl_VII">28</a>.</p> - -<p class="mt2em">We now cast a rapid glance at the wings of -insects.</p> - -<p>They have no analogy, except in their use, with -the wings of birds, as they are not modifications of -existing limbs, but entirely separate organs. They -consist of two membranes united at their edges, -and traversed and supported by sundry hollow -branches or “nervures,” which admit air, and serve -as useful guides to entomologists for separating the -insects into their genera. Indeed, the general -character of the wings has long been employed as -the means of dividing the insect race into their -different orders, as may be seen in any work on -entomology. The typical number of wings is four, -but it often happens that two are almost wholly -absent, or that the uppermost pair are thickened -into a shelly kind of substance which renders them -useless for flight; while in many insects, such as -the ground beetles and others, the upper wings -become hardened into firm coverings for the body, -and the lower pair are shrivelled and useless.</p> - -<p><span class="pagenum" title="111"><a name="Page_111" id="Page_111"></a></span></p> - -<p>Fig. <a href="#Pl_VII">22</a> shows two of the wings of a humble -bee, together with their nervures, and the peculiar -system by which the upper and lower pair are -united together at the will of the insect. At the -upper edge of the lower wing, and nearly at its -extremity, may be seen a row of very tiny hooks, -shown on a larger scale at Fig. <a href="#Pl_VII">25</a>. These hooklets -hitch into the strengthened membrane of the upper -wing, which is seen immediately above them, and -so conjoin the two together. The curious wing-hooks -of the Aphis may be seen on Fig. <a href="#Pl_VII">24</a>, very -highly magnified.</p> - -<p>Fig. <a href="#Pl_VII">31</a> is the wing of the midge (<i>Psychóda</i>), -that odd little insect which is seen hopping and -popping about on the windows of outhouses and -similar localities, and is so hard to catch. The -whole wing is plentifully covered with elongated -scales, and is a most lovely object under any power -of the microscope. These scales run along the -nervures and edges of the wings, and part of a -nervure is shown more highly magnified at -Fig. <a href="#Pl_VII">32</a>.</p> - -<p>At Fig. <a href="#Pl_VII">23</a> is shown the wing of one of the -hemipterous insects, common along the banks of -ditches and in shady lanes, and known by the -name of Cíxius. It is remarkable for the numerous -spots which stud the nervures, one being always -found at each forking, and the others being very -irregularly disposed.</p> - -<p>Fig. <a href="#Pl_VII">30</a> is one of the balancers or “haltéres” of -the house-fly. These organs are found in all the -two-winged insects, and are evidently modifications<span class="pagenum" title="112"><a name="Page_112" id="Page_112"></a></span> -of the second pair of wings. They are covered -with little vesicles, and protected at their base by -scales. Some writers suppose that the sense of -smell resides in these organs. Whatever other -purpose they may serve, they clearly aid in the -flight, as, if the insect be deprived of one or both -of the balancers, it has the greatest difficulty in -steering itself through the air.</p> - -<p>The wings of insects are mostly covered with -hairs or scales, several examples of which are given -in Plate VIII. Fig. <a href="#Pl_VIII">4</a> shows one of the scales of -the Adippe or fritillary butterfly, exhibiting the -double membrane—part of which has been torn -away—and the beautiful lines of dots with which -it is marked. The structure of the scales is further -shown by a torn specimen of tiger moth scale -seen on Fig. <a href="#Pl_VIII">16</a>. On many scales these dots -assume a “watered” aspect when the focus or -illumination changes, an example of which may be -seen in Fig. <a href="#Pl_VIII">15</a>, a scale of the peacock butterfly.</p> - -<p>Fig. <a href="#Pl_VIII">11</a> is one of the ordinary scales of the azure -blue butterfly, and Fig. <a href="#Pl_VIII">10</a> shows one of the curious -“battledore” scales of the same insect, with its -rows of distinct dottings. Fig. <a href="#Pl_VIII">14</a> is one of the -prettily tufted scales of the orange-tip butterfly, -and Fig. <a href="#Pl_VIII">8</a> is the splendid branched scale of the -death’s-head moth. Fig. <a href="#Pl_VIII">19</a> shows a scale of the -sugar-runner (<i>Lepisma saccharína</i>), a little silvery -creature with glistening skin, and long bristles at -the head and tail, that is found running about -cupboards, window-sills, and similar places. It is -not easy to catch with the fingers, as it slips -through them like oil; but by holding a cover-glass -in a pair of forceps, and pressing it upon one of -the little creatures, a number of the scales may be -caused to adhere to it, and these should be mounted -dry for examination. The gnats also possess very -pretty scales, with the ribs projecting beyond the -membrane.</p> - - -<p class="tac">VII.</p> - -<div class="center"> -<table border="0" cellpadding="0" cellspacing="0" summary="Key to Plate VII"> -<tr><td class="tar pr05 fs70">FIG.</td></tr> -<tr><td class="tar pr05">1.</td><td class="tal">Tongue, Hive Bee</td><td class="tar prl05 bl">18.</td><td class="tal"> Do.  Dung fly</td></tr> -<tr><td class="tar pr05">2.</td><td class="tal"> Do.  Tortoiseshell Butterfly</td><td class="tar prl05 bl">19.</td><td class="tal"> Do.  Asilus</td></tr> -<tr><td class="tar pr05">3.</td><td class="tal"> Do.  do. one of the barrel-shaped bodies </td><td class="tar prl05 bl">20.</td><td class="tal"> Do.  Acarus of Dor-beetle</td></tr> -<tr><td class="tar pr05">4.</td><td class="tal">Head, Violet Ground Beetle (Carabus)</td><td class="tar prl05 bl">21.</td><td class="tal">Claws and Pad, Ophion</td></tr> -<tr><td class="tar pr05">5.</td><td class="tal">Tongue, Cricket</td><td class="tar prl05 bl">22.</td><td class="tal">Wings, Humble Bee</td></tr> -<tr><td class="tar pr05">6.</td><td class="tal"> Do.  do.</td><td class="tar prl05 bl">23.</td><td class="tal"> Do.</td></tr> -<tr><td class="tar pr05">7.</td><td class="tal">Head, Scorpion Fly (Panorpa)</td><td class="tar prl05 bl">24.</td><td class="tal">Wing hooks, hind wing of Aphis</td></tr> -<tr><td class="tar pr05">8.</td><td class="tal">Leg, Ant</td><td class="tar prl05 bl">25.</td><td class="tal">Wing hooks, Humble Bee</td></tr> -<tr><td class="tar pr05">9.</td><td class="tal">Proleg, Caterpillar</td><td class="tar prl05 bl">26.</td><td class="tal">Foot, Flea</td></tr> -<tr><td class="tar pr05">10.</td><td class="tal"> Do.  do. single hook</td><td class="tar prl05 bl">27.</td><td class="tal">Stomach and gastric teeth, Bee</td></tr> -<tr><td class="tar pr05">11.</td><td class="tal">Proboscis, Fly</td><td class="tar prl05 bl">28.</td><td class="tal">Three teeth of do.</td></tr> -<tr><td class="tar pr05">12.</td><td class="tal"> Do.  do.  “modified trachea”</td><td class="tar prl05 bl">29.</td><td class="tal">Cast skin, Larva of Tortoise Beetle (Cassida)</td></tr> -<tr><td class="tar pr05">13.</td><td class="tal">Part of Foreleg of Water Beetle (Acilius) </td><td class="tar prl05 bl">30.</td><td class="tal">Balancer, Blow fly</td></tr> -<tr><td class="tar pr05">14.</td><td class="tal"> Do.  large sucker</td><td class="tar prl05 bl">31.</td><td class="tal">Wing, Midge (Psychoda)</td></tr> -<tr><td class="tar pr05">15.</td><td class="tal">Leg, long-legged Spider (Phalangium)</td><td class="tar prl05 bl">32.</td><td class="tal"> Do.  do.  part of a nervure with scales</td></tr> -<tr><td class="tar pr05">16.</td><td class="tal"> Do.  Harvest-bug (Trombidium)</td><td class="tar prl05 bl">33.</td><td class="tal">Stomach and gastric teeth, Grasshopper</td></tr> -<tr><td class="tar pr05">17.</td><td class="tal"> Do.  Glow-worm</td><td class="tar prl05 bl">34.</td><td class="tal">Spiracle, Wire-worm</td></tr> -</table></div> - -<div class="figcenter" style="width: 442px;"> -<a id="Pl_VII"></a> -<img src="images/i_p_007.jpg" width="442" height="700" alt="" /> -<div class="caption"><p>VII.</p></div> -</div> - -<p><span class="pagenum" title="113"><a name="Page_113" id="Page_113"></a></span></p> - -<p>Fig. <a href="#Pl_VIII">21</a> is a scale from the common spring-tail -(<i>Podúra plúmbea</i>), a little creature which is found -plentifully in cellars and other damp places, skipping -about with great activity. Some flour scattered -on a piece of paper is a sure trap for these little -beings. Fig. <a href="#Pl_VIII">3</a> is one of the scales taken from the -back of the celebrated diamond beetle, showing -the cause of the magnificent gem-like aspect of -that insect. We have in England many beetles of -the same family—the weevils—which, although -much smaller, are quite as splendid when exhibited -under a microscope by reflected light. The wing-case -or “elytron” of a little green weevil, very -common in the hedges, may be seen on Plate XII. -Fig. <a href="#Pl_XII">10</a>.</p> - -<p>The reader will observe that all these scales are -furnished with little root-like appendages, by means -of which they are affixed to the insect. Fig. <a href="#Pl_VIII">13</a> -shows a portion of the wing of the azure blue -butterfly, from which nearly all the scales have -been removed, for the purpose of exhibiting the -pits or depressions in which they had formerly -been fastened, and one or two of the scales are -left still adherent to their places. The scales are -arranged in equal rows like the slates of a housetop,<span class="pagenum" title="114"><a name="Page_114" id="Page_114"></a></span> -as may be seen on Fig. <a href="#Pl_VIII">18</a>, which represents part -of the same wing, to show the scales overlapping -each other, and the elegant form which they take -near the edges of the wing, so as to form a delicate -fringe. The long hair-like down which covers the -legs and bodies of the moths and butterflies (which -are called Lepidóptera, or scale-winged insects, in -consequence of this peculiarity), is seen under the -microscope to be composed of scales very much -elongated, as is shown in Fig. <a href="#Pl_VIII">17</a>, a portion taken -from the leg of a tiger moth.</p> - -<p class="mt2em">The eggs of insects are all very beautiful, and -three of the most curious forms are given on -Plate VIII.</p> - -<p>Fig. <a href="#Pl_VIII">2</a> is the empty egg of the gad-fly, as it -appears when fastened to a hair of the horse. -Fig. <a href="#Pl_VIII">5</a> represents the pretty ribbed egg of the -common tortoise-shell butterfly; and Fig. <a href="#Pl_VIII">7</a> is -the very beautiful egg of the very horrid bed-bug, -worthy of notice on account of the curious lid -with which its extremity is closed, by means of -which the young larva creeps out as soon as it is -hatched.</p> - -<p>The feathers of birds, and the fur of animals, -will furnish many examples of the eggs of parasites, -some of which are of extreme beauty. The feather -or hair may be mounted in a cell without disturbing -the eggs, which should, however, be heated -sufficiently to kill the embryo if present.</p> - -<p>Fig. <a href="#Pl_VIII">9</a> shows the penetrating portions of the sting -of the wasp. The two barbed stings, which seem<span class="pagenum" title="115"><a name="Page_115" id="Page_115"></a></span> -to be the minute prototypes of the many-barbed -spears of the South Sea islanders, are seen lying -one at each side of their sheath, and a single barb -is drawn a little to the left on a very much larger -scale. It is by reason of these barbs that the -sting is always left adhering to the wound, and is -generally drawn wholly out of the insect, causing -its death in a short while.</p> - -<p>The sting is only found in female insects, and is -supposed to be analogous to the “ovipositor” of -other insects, <i>i.e.</i> the instrument by which the -eggs are deposited in their places. Fig. <a href="#Pl_VIII">20</a> shows -the curious egg-placing apparatus of one of the -saw-flies. The backs of these “saws” work in -grooves, and they work alternately, so that the -fly takes but a very short time in cutting a slit -in the young bark of a tender shoot, and laying -her eggs in the slit. When she has completed -one of these channels, she sets to work upon -another, and in the early spring the young branches -of the gooseberry bushes may be seen plentifully -covered with these grooves and the eggs. When -hatched, black caterpillar-like grubs from the eggs -issue, and devastate the bushes sadly, turning in -process of time into blackish flies, which are seen -hovering in numbers over the gooseberries, and may -be killed by thousands.</p> - -<p class="mt2em">The scales and hairs of other animals deserve -great attention. Fig. <a href="#Pl_VIII">23</a> is a single hair of the -human beard, as it often appears when tied in a -knot—by Queen Mab and her fairies, according<span class="pagenum" title="116"><a name="Page_116" id="Page_116"></a></span> -to Mercutio. Fig. <a href="#Pl_VIII">22</a> is a portion of the same -hair as it appears when splitting at its extremity. -The structure of the hair is not, however, so well -seen in this object as in that represented on Fig. <a href="#Pl_VIII">24</a>, -which is a beautiful example of white human -hair that once adorned the head of the victor of -Waterloo. It formed one of a tiny lock given to -me by a friend, and is so admirable an example of -human hair, that I forthwith mounted it for the -microscope. In this hair the cells may be seen -extending down its centre, and the peculiar -roughened surface produced by the flattened cells -which are arranged around its circumference are -also seen. By steeping in caustic potash, these -scales can be separated, but generally they lie -along the hair in such a manner that if the hair -be drawn through the fingers from base to point, -their projecting ends permit it to pass freely; -whilst if it be drawn in the reverse direction, they -cause it to feel very harsh to the touch.</p> - -<p>In the sheep’s wool (Fig. <a href="#Pl_VIII">30</a>) this structure is -much more developed, and gives to the fibres the -“felting” power that causes them to interlace so -firmly with each other, and enables cloth—when -really made of wool—to be cut without unravelling. -Fig. <a href="#Pl_VIII">37</a> is the smooth hair of the badger; and -Fig. <a href="#Pl_VIII">34</a> is the curious hair of the red deer, which -looks as if it had been covered with a delicate -net.</p> - -<p>Fig. <a href="#Pl_VIII">28</a> is the soft, grey, wool-like hair of the -rat; and Fig. <a href="#Pl_VIII">29</a> is one of the larger hairs that -protrude so plentifully, and form the glistening<span class="pagenum" title="117"><a name="Page_117" id="Page_117"></a></span> -brown coat of that animal. Fig. <a href="#Pl_VIII">38</a> is the curiously -knobbed hair of the long-eared bat, the knobs -being formed of protuberant scales that can easily -be scraped off. Fig. <a href="#Pl_VIII">31</a> shows a hair of the -common mole; and Fig. <a href="#Pl_VIII">32</a> is one of the long -hairs of the rabbit. Fig. <a href="#Pl_VIII">27</a> is a flat hair of the -dormouse, slightly twisted, the difference in the -breadth showing where the twist has taken place. -The hair of the mouse is beautifully ribbed, so as -to look like a ladder. Fig. <a href="#Pl_VIII">26</a> is one of the very -long hairs that so thickly clothe the tiger moth -caterpillar; and Fig. <a href="#Pl_VIII">25</a> is a beautifully branched -hair taken from the common humble bee.</p> - -<p>All hairs should be examined by polarised light, -with a plate of selenite, when most gorgeous colour -effects may be obtained.</p> - -<p>The four fibres mostly used in the manufacture -of apparel are: wool, Fig. <a href="#Pl_VIII">30</a>, which has already -been described; linen, Fig. <a href="#Pl_VIII">39</a>; cotton, Fig. <a href="#Pl_VIII">40</a>; -and silk, Fig. <a href="#Pl_VIII">41</a>. The structure of each is very -well marked and easily made out with the microscope; -so that an adulterated article can readily -be detected by a practised eye. Cotton is the -most common adulteration of silk and linen fabrics, -and may at once be detected by its flat twisted -fibre. Silk is always composed of two parallel -threads, each proceeding from one of the spinnerets -of the caterpillar, and it may be here remarked -that if these threads are not quite parallel the silk -is of bad quality. Silken fibre is always covered, -when new, with a kind of varnish, usually of a -bright orange colour, which gives the undressed<span class="pagenum" title="118"><a name="Page_118" id="Page_118"></a></span> -“floss” silk its peculiar hue, but which is soluble -and easily washed away in the course of manufacture.</p> - -<p>Figs. <a href="#Pl_VIII">35</a> and 36 are the small and large hairs of -that magnificent creature, the sea mouse (<i>Aphrodíte -aculeáta</i>), whose covering, although it lies in the -mud, glows with every hue of the rainbow, and in -a brilliant light is almost painfully dazzling to the -eye.</p> - -<p class="tac">VIII.</p> - -<div class="center"> -<table border="0" cellpadding="0" cellspacing="0" summary="Key to Plate VIII"> -<tr><td class="tar pr05 fs70">FIG.</td></tr> -<tr><td class="tar pr05">1.</td><td class="tal">Boat-fly, leg</td><td class="tar prl05 bl">23.</td><td class="tal"> Do.  Human Beard</td></tr> -<tr><td class="tar pr05">2.</td><td class="tal">Gadfly, empty egg</td><td class="tar prl05 bl">24.</td><td class="tal"> Do.  do.  aged</td></tr> -<tr><td class="tar pr05">3.</td><td class="tal">Diamond Beetle, scale</td><td class="tar prl05 bl">25.</td><td class="tal"> Do.  Humble Bee</td></tr> -<tr><td class="tar pr05">4.</td><td class="tal">Scale, Fritillary, Adippe</td><td class="tar prl05 bl">26.</td><td class="tal"> Do.  Tiger Moth, Larva</td></tr> -<tr><td class="tar pr05">5.</td><td class="tal">Egg, Tortoiseshell Butterfly</td><td class="tar prl05 bl">27.</td><td class="tal"> Do.  Dormouse</td></tr> -<tr><td class="tar pr05">6.</td><td class="tal">Head and Eyes, Zebra Spider</td><td class="tar prl05 bl">28.</td><td class="tal"> Do.  Rat</td></tr> -<tr><td class="tar pr05">7.</td><td class="tal">Eyes, Bed-Bug</td><td class="tar prl05 bl">29.</td><td class="tal"> Do.  do.  long hair</td></tr> -<tr><td class="tar pr05">8.</td><td class="tal">Scale, Death’s-Head Moth</td><td class="tar prl05 bl">30.</td><td class="tal"> Do.  Sheep</td></tr> -<tr><td class="tar pr05">9.</td><td class="tal">Sting, Wasp</td><td class="tar prl05 bl">31.</td><td class="tal"> Do.  Mole</td></tr> -<tr><td class="tar pr05">10.</td><td class="tal">Scale, battledore, Azure blue</td><td class="tar prl05 bl">32.</td><td class="tal"> Do.  Rabbit</td></tr> -<tr><td class="tar pr05">11.</td><td class="tal"> Do.  ordinary scale</td><td class="tar prl05 bl">33.</td><td class="tal">Scale, Greenbone Pike</td></tr> -<tr><td class="tar pr05">12.</td><td class="tal">Eye, Harvest Spider</td><td class="tar prl05 bl">34.</td><td class="tal">Hair, Red Deer</td></tr> -<tr><td class="tar pr05">13.</td><td class="tal">Wing Membrane, Azure Blue </td><td class="tar prl05 bl">35.</td><td class="tal"> Do.  fine, Sea Mouse</td></tr> -<tr><td class="tar pr05">14.</td><td class="tal">Scale, Anthocera cardaminis</td><td class="tar prl05 bl">36.</td><td class="tal"> Do.  do.  large</td></tr> -<tr><td class="tar pr05">15.</td><td class="tal"> Do.  Peacock Butterfly</td><td class="tar prl05 bl">37.</td><td class="tal"> Do.  do.  Badger</td></tr> -<tr><td class="tar pr05">16.</td><td class="tal"> Do.  Tiger Moth</td><td class="tar prl05 bl">38.</td><td class="tal"> Do.  do.  long-eared Bat</td></tr> -<tr><td class="tar pr05">17.</td><td class="tal"> Do.  Thigh of Tiger Moth</td><td class="tar prl05 bl">39.</td><td class="tal">Fibre, Linen</td></tr> -<tr><td class="tar pr05">18.</td><td class="tal">Wing and Scales, Azure Blue </td><td class="tar prl05 bl">40.</td><td class="tal"> Do.  Cotton</td></tr> -<tr><td class="tar pr05">19.</td><td class="tal">Scale, Lepisma</td><td class="tar prl05 bl">41.</td><td class="tal"> Do.  Silk</td></tr> -<tr><td class="tar pr05">20.</td><td class="tal">Saws, Sawfly</td><td class="tar prl05 bl">42.</td><td class="tal">Scale, Perch</td></tr> -<tr><td class="tar pr05">21.</td><td class="tal">Scale, Podura</td><td class="tar prl05 bl">43.</td><td class="tal"> Do.  do.</td></tr> -<tr><td class="tar pr05">22.</td><td class="tal">Hair, Black Human</td><td class="tar prl05 bl"></td><td class="tal"></td></tr> -</table></div> - -<div class="figcenter" style="width: 437px;"> -<a id="Pl_VIII"></a> -<img src="images/i_p_008.jpg" width="437" height="700" alt="" /> -<div class="caption"><p>VIII.</p></div> -</div> - -<p>The scales of some of the fishes are shown on -Plate <a href="#Pl_VIII">VIII</a>., in order to exhibit their mode of -growth by successive layers. The scales are always -enveloped in membranous sacs, and in some cases, -as in the eel, they do not project beyond the -surface, and require some little observation to -detect them. A scale of an eel is shown on Plate XI. -Fig. <a href="#Pl_XI">14</a>, and is a magnificent object under -polarised light. Fig. <a href="#Pl_VIII">33</a> is a scale of the greenbone -pike; and Figs. <a href="#Pl_VIII">42</a> and 43 are scales of the perch, -showing the roots by which they are held in their -places. The roach, dace, bleak, and many other -similar fish have a beautiful silvery substance on -the under surface of the scales, which was greatly -used in the manufacture of artificial pearls, glass -beads being thinly coated in the interior with the -glittering substance, and then filled in with wax. -A piece of sole-skin, when preserved in Canada -balsam and placed under the microscope, is a very -beautiful object.</p> - -<p>More examples of hairs, and other processes -from the skin, together with the structure of the<span class="pagenum" title="119"><a name="Page_119" id="Page_119"></a></span> -skin itself, of bone, of blood, and the mode in -which it circulates, are given on Plate <a href="#Pl_X">X</a>.</p> - -<p>In all important points of their structure the -feathers of birds are similar to the hairs of animals, -and are developed in a similar manner. They are -all composed of a quill portion, in which the pith -is contained, and of a shaft, which carries the vane, -together with its barbs. The form of each of these -portions varies much, even in different parts of the -same bird, and the same feather has almost always -two kinds of barbs; one close and firm, and the -other loose, floating, and downy. If a small feather -be plucked from the breast or back of a sparrow or -any other small bird, the upper part of the feather -is seen to be close and firm, while the lower is -loose and downy, the upper part being evidently -intended to lie closely on the body and keep out -the wet, while the lower portion affords a soft and -warm protection to the skin.</p> - -<p>Fig. <a href="#Pl_X">12</a>, Plate X., shows the feather of a peacock, -wherein the barbs are very slightly fringed and lie -quite loosely side by side. Fig. <a href="#Pl_X">18</a> is part of -the same structure, in a duck’s feather, wherein -are seen the curious hooks which enable each -vane to take a firm hold of its neighbour, the -whole feather being thus rendered firm, compact, -and capable of repelling water. The reader will -not fail to notice the remarkable analogy between -these hooks and those which connect the wings of -the bee.</p> - -<p>Fig. <a href="#Pl_X">17</a> is a part of the shaft of a young feather -taken from the canary, given for the purpose of<span class="pagenum" title="120"><a name="Page_120" id="Page_120"></a></span> -showing the form of the cells of which the pith -is composed. Fig. <a href="#Pl_X">20</a> is part of the down from a -sparrow’s feather, showing its peculiar structure; -and Fig. <a href="#Pl_X">21</a> is a portion of one of the long drooping -feathers of the cock’s tail.</p> - -<p>Fig. <a href="#Pl_X">13</a> exhibits a transverse section of one of -the large hairs or spines from the hedgehog, and -shows the disposition of the firm, horn-like exterior, -and the arrangement of the cells. Sections of -various kinds of hair are interesting objects, and -are easily made by tying a bundle of them together, -soaking them in gum, hardening in spirit, and then -cutting thin slices with a razor. A little glycerine -will dissolve the gum, and the sections of hair will -be well shown. Unless some such precaution be -taken, the elasticity of the hair will cause the tiny -sections to fly in all directions, and there will be -no hope of recovering them.</p> - -<p>Several examples of the skin are also given. -Fig. <a href="#Pl_X">27</a> is a section through the skin of the human -finger, including the whole of one of the little -ridges which are seen upon the extremity of every -finger, and half of two others. The cuticle, epidermis, -or scarf-skin, as it is indifferently termed, -is formed of cells or scales, much flattened and -horny in the upper layers, rounder and plumper -below. The true skin, or “cutis,” is fibrous in -structure, and lies immediately beneath, the two -together constituting the skin, properly so called. -Beneath lies a layer of tissue filled with fatty -globules, and containing the glands by which the -perspiration is secreted.</p> - -<p><span class="pagenum" title="121"><a name="Page_121" id="Page_121"></a></span></p> - -<p>One of the tubes or channels by which these -glands are enabled to pour their contents to the -outside of the body, and, if they be kept perfectly -clean, to disperse them into the air, is seen running -up the centre of the figure, and terminating in a -cup-shaped orifice on the surface of the cuticle. -On the palm of the hand very nearly three thousand -of these ducts lie within the compass of a -square inch, and more than a thousand in every -square inch of the arm and other portions of the -body, so that the multitude of these valuable -organs may be well estimated, together with the -absolute necessity for keeping the skin perfectly -clean in order to enjoy full health.</p> - -<p>Fig. <a href="#Pl_X">1</a> shows a specimen of epidermis taken from -the skin of a frog, exhibiting the flattened cells -which constitute that structure, and the oval or -slightly elongated nuclei, of which each cell has -one. In Fig. <a href="#Pl_X">32</a>, a portion of a bat’s wing, the -arrangement of the pigment is remarkably pretty. -Immediately above, at Fig. <a href="#Pl_X">31</a>, is some of the -pigment taken from the back of the human eye-ball. -The shape of the pigment cells is well -shown. Similar specimens may easily be obtained -from the back of a sheep’s eye which has been hardened -in spirit, or from that of a boiled fish. Fig. <a href="#Pl_X">33</a> -shows the pigment in the shell of the prawn.</p> - -<p class="mt2em">On various parts of animal structures, such as -the lining of internal cavities, the interior of the -mouth, and other similar portions of the body, the -cells are developed into a special form, which is<span class="pagenum" title="122"><a name="Page_122" id="Page_122"></a></span> -called “Epithélium,” and which corresponds to the -epidermis of the exterior surface of the body. The -cells which form this substance are of different -shapes, according to their locality. On the tongue, -for example (for which see Fig. <a href="#Pl_X">11</a>), they are -flattened, and exhibit their nucleus, in which the -nucléolus may be discovered with a little care. -Cells of this kind are rounded, as in the case just -mentioned, or angular, and in either case they are -termed squamous (<i>i.e.</i>, scaly) epithelium. Sometimes -they are like a number of cylinders, cones, or -pyramids, ranged closely together, and are then -called cylindrical epithelium. Sometimes the free -ends of cylindrical epithelium are furnished with a -number of vibrating filaments or cilia, and in this -case the structure is called “ciliated” epithelium. -Cylindrical epithelium may be found in the ducts -of the glands which open into the intestines, as -well as in the glands that secrete tears; and -ciliated epithelium is seen largely in the windpipe, -the interior of the nose, etc. A specimen taken -from the nose is seen at Fig. <a href="#Pl_X">15</a>. A beautiful -example of ciliated epithelium is to be found in -the gills of the mussel. A portion of one of the -yellowish bands which lie along the edge of the -shell on the opening side is carefully removed -with sharp scissors, and examined in the shell-liquor, -being protected from pressure by placing -a piece of paper beneath each end of the cover-glass. -Such a preparation is shown in Plate IX. -Fig. <a href="#Pl_IX">39</a>, but no drawing can give an idea of its -wonderful beauty and interest. The cilia will<span class="pagenum" title="123"><a name="Page_123" id="Page_123"></a></span> -continue to move for a long time after removal -from the shell.</p> - -<p class="mt2em">Bone in its various stages is figured on Plate X.</p> - -<p>Fig. <a href="#Pl_X">9</a> is a good example of human bone, and is -a thin transverse section taken from the thigh. -When cut across, bone exhibits a whitish structure -filled with little dottings that become more numerous -towards the centre, and are almost invisible -towards the circumference. In the centre of the -bone there is a cavity, which contains marrow in -the mammalia and air in the birds. When placed -under a microscope, bone presents the appearance -shown in the illustration.</p> - -<p>The large aperture in the centre is one of innumerable -tubes that run along the bone, and serve -to allow a passage to the vessels which convey blood -from one part of the bone to another. They are -technically called Haversian canals, and if a longitudinal -section be made they will be found running -tolerably parallel, and communicating freely with -each other. Around each Haversian canal may be -seen a number of little black spots with lines -radiating in all directions, and looking something -like flattened insects. These are termed bone-cells -or “lacúnæ,” and the little black lines are called -“canalículi.” In the living state they contain cells -which are concerned in the growth of the bone, and -these may be made evident by softening fresh bone -with acid, cutting sections of it, and staining. -When viewed by transmitted light the lacunæ and -canaliculi are black; but when seen by dark-field<span class="pagenum" title="124"><a name="Page_124" id="Page_124"></a></span> -illumination the Haversian canals become black, -and the lacunæ are white.</p> - -<p>As these canaliculi exist equally in every direction, -it is impossible to make a section of bone -without cutting myriads of them across; and when -a high power is employed they look like little dots -scattered over the surface. A very pretty object -can be made of the bone taken from a young animal -which has been fed with madder, as the colour gets -into the bone and settles chiefly round the Haversian -canal. A young pig is a very good subject, so -is a rabbit.</p> - -<p>Fig. <a href="#Pl_X">16</a> is a similar section cut from the leg-bone -of an ostrich.</p> - -<p>The development of bone is beautifully shown in -Fig. <a href="#Pl_X">30</a>, a delicate slice taken from a pig’s rib. -Above may be seen the gristle or cartilage, with the -numerous rows of cells; below is the formed bone, -with one of the Haversian canals and its contents; -while between the two may be seen the cartilage-cells -gathering together and arranging themselves -into form. The cartilage-cells are well shown in -Fig. <a href="#Pl_X">28</a>, which is a portion of the cup which had -contained the eye of a haddock.</p> - -<p>The horn-like substances at the end of our fingers, -which we call the nails, are composed of innumerable -flattened cells. These cells are generally so fused -together as to be quite indistinguishable even with -a microscope, but can be rendered visible by soaking -a section of nail in liquor potassæ, which causes the -cells to swell up and resume to a degree their -original rounded form.</p> - -<p><span class="pagenum" title="125"><a name="Page_125" id="Page_125"></a></span></p> - -<p>It is worthy of remark that the animal form is -built up of cells, as is the case with the vegetables, -although the cells are not so variable in shape. -They generally may be found to contain well-marked -nuclei, two or more of the latter being often found -within a single cell, and in many cases the tiny -nucleoli are also visible. Good examples of these -cells may be obtained from the yolk of an egg, and -by careful management they may be traced throughout -every part of the animal form.</p> - -<p>The teeth have many of the constituents of bone, -and in some of their parts are made after precisely -the same fashion. When cut, the teeth are seen to -consist of a hard substance, called enamel, which -coats their upper surfaces, of dentine, or ivory, -within the enamel, and of “cement,” which surrounds -the fangs. In Fig. <a href="#Pl_X">26</a>, Plate X., which is -a longitudinal section of the human “eye” tooth, is -seen the ivory occupying the greater part of the -tooth, coated by the enamel at the top and the -cement at the bottom. In the centre of each tooth -there is a cavity, which is plentifully filled with a -pulpy substance by which the tooth is nourished, -and which conveys the nerves which endow it with -sensation. A traverse section of the same tooth is -seen in Fig. <a href="#Pl_X">25</a>.</p> - -<p>The enamel is made of little elongated prisms, all -pointing to the centre of the tooth. When viewed -transversely, their ends are of a somewhat hexagonal -shape, something like an irregular honeycomb. The -dentine is composed of a substance pierced with -myriads of minute tubes. They require a rather<span class="pagenum" title="126"><a name="Page_126" id="Page_126"></a></span> -high power—say 300 diameters—to show them -properly. The cement is found at the root of the -fangs, and is best shown in the tooth of an aged -individual, when it assumes very clearly the character -of bone.</p> - -<p>Sections may be made by sawing a slice in the -required direction, polishing one side, and cementing -it with old Canada balsam to a slide. It may then -be filed down to nearly the required thinness, -finished by carefully rubbing with a hone, and -polished with buff leather. Canada balsam may -then be dropped upon it, and a glass cover pressed -firmly down.</p> - -<p>Sections of young bone form magnificent objects -for the polariser.</p> - -<p>Fig. <a href="#Pl_X">29</a> is a section cut from one of the palate -teeth of the ray (<i>Myliobátes</i>).</p> - -<p>A rather important element in the structure of -animals is the “elastic ligament,” which is found -in the back of the neck and other parts of the body, -especially about the spine. It is made of a vast -number of fibres of variable shape and length, -branching and communicating, arranged generally -in bundles, and remarkable for containing very few -vessels, and no nerves at all. At Fig. <a href="#Pl_X">14</a> may be -seen an example of elastic ligament, popularly called -“paxwax,” taken from the neck of a sheep.</p> - -<p>The white fibrous tissue by which all the parts -of the body are bound together is seen at Fig. <a href="#Pl_X">10</a>; -and at Fig. <a href="#Pl_X">11</a> is a beautiful example of the -“ultimate fibres” of the crystalline lens of a -sturgeon’s eye.</p> - -<p><span class="pagenum" title="127"><a name="Page_127" id="Page_127"></a></span></p> - -<p>The muscles of animals are of two kinds, the one -termed the striped, and the other the unstriped. -Of these, the latter belongs to organs which work -independently of will, such as the stomach, etc., -while the former belongs to those portions of the -body which are subject to voluntary motion, such -as the arm and the leg. The unstriped muscle is -very simple, consisting merely of long spindle-shaped -cells, but the striped or voluntary muscle is of more -complex construction. Every voluntary muscle -consists of myriads of tiny fibres, bound together in -little bundles, enveloped in a kind of sheath. -Fig. <a href="#Pl_X">24</a> is an example of this muscular fibre, taken -from beef. When soaked in spirit, it often splits -into a number of discs, the edges of which are -marked by the transverse lines.</p> - -<p>A fibre of nerve is drawn at Fig. <a href="#Pl_X">23</a>, and is given -for the purpose of showing the manner in which the -nerve is contained in and protected by its sheath, -just like a telegraph-wire in its coverings. Just -above is a transverse section of the same fibre, -showing the same arrangement from another point -of view, and also illustrating the curious phenomenon, -that when nerve-fibres are treated with -carmine the centre takes up the colouring matter, -while the sheath remains white as before. The -best way of studying nerves is to decapitate a frog, -and cut off a piece of one of the nerves, which, like -fine silk threads, come out between the joints of the -spine inside the abdomen. By careful teasing out -it is easy to obtain preparations showing all the -above points, and, in addition, the folding-in of the<span class="pagenum" title="128"><a name="Page_128" id="Page_128"></a></span> -internal sheath which correspond to the insulators -of a telegraph-line.</p> - -<p>The blood of animals is analogous in its office to -the sap of plants, but differs greatly from it under -the microscope. In sap there seem to be no -microscopic characters, except that when a branch -is cut, as in the vine, the flowing sap may contain -certain substances formed in the wounded cells, such -as chlorophyll, starch, and raphides; but the blood -is known to be an exceedingly complex substance -both in a microscopic and a chemical point of view. -When a little fresh blood is placed under the -microscope, it is seen to consist of a colourless fluid -filled with numerous little bodies, commonly called -“blood-globules,” varying very greatly in size and -shape, according to the animal from which they -were taken. Those of the reptiles are very large, -as may be seen at Fig. <a href="#Pl_X">4</a>, Plate X., which represents -a blood corpuscle of the Proteus. In this curious -reptile the globules are so large that they may be -distinguished during its life by means of a common -pocket lens.</p> - -<p>In the vertebrated animals these corpuscles are -red, and give to the blood its peculiar tint. They -are accompanied by certain colourless corpuscles, -spherical in form, which are sometimes, as in man, -larger than the red globules, and in others, as in the -siren and the newt, considerably smaller. The -general view of the red corpuscles has sufficient -character to enable the practised observer to name -the class of animal from which it was taken, and in -some cases they are so distinctive that even the -genus can be ascertained with tolerable certainty. -In point of size, the reptiles have the largest and -the mammalia the smallest, those of the Proteus -and the musk-deer being perhaps the most decidedly -opposed to each other in this respect.</p> - - -<p class="tac">IX.</p> - -<div class="center"> -<table border="0" cellpadding="0" cellspacing="0" summary="Key to Plate IX"> -<tr><td class="tar pr05 fs70">FIG.</td></tr> -<tr><td class="tar pr05">1.</td><td class="tal">Amœba diffluens</td><td class="tar prl05 bl">21.</td><td class="tal">Head of Snake-headed Zoophyte</td></tr> -<tr><td class="tar pr05">2.</td><td class="tal">Arcella</td><td class="tar prl05 bl">22.</td><td class="tal">Bugula avicularia</td></tr> -<tr><td class="tar pr05">3.</td><td class="tal">Sun animalcule</td><td class="tar prl05 bl">23.</td><td class="tal">Polyzoön, Eretea</td></tr> -<tr><td class="tar pr05">4.</td><td class="tal">Miliolina</td><td class="tar prl05 bl">24.</td><td class="tal"> Do.  Notamia</td></tr> -<tr><td class="tar pr05">5.</td><td class="tal">Paramœcium</td><td class="tar prl05 bl">25.</td><td class="tal">Zoea, Young of Crab</td></tr> -<tr><td class="tar pr05">6.</td><td class="tal">Chilodon subdividing</td><td class="tar prl05 bl">26.</td><td class="tal">Hydra tuba</td></tr> -<tr><td class="tar pr05">7.</td><td class="tal">Melicerta ringens</td><td class="tar prl05 bl">27.</td><td class="tal">Medusa, cast off from above</td></tr> -<tr><td class="tar pr05">8.</td><td class="tal">Spicula of Sponge, Grantia</td><td class="tar prl05 bl">28.</td><td class="tal">Naked-eyed Medusa, Thaumantias</td></tr> -<tr><td class="tar pr05">9.</td><td class="tal">Noctiluca miliaris</td><td class="tar prl05 bl">29.</td><td class="tal">Compound Eye, Medusa</td></tr> -<tr><td class="tar pr05">10.</td><td class="tal">Rotifer vulgaris</td><td class="tar prl05 bl">30.</td><td class="tal">Larva, Snake Star</td></tr> -<tr><td class="tar pr05">11.</td><td class="tal"> Do.  jaws</td><td class="tar prl05 bl">31.</td><td class="tal">Water Flea</td></tr> -<tr><td class="tar pr05">12.</td><td class="tal">Sponge animalcule</td><td class="tar prl05 bl">32.</td><td class="tal">Serpula, Pushing Pole</td></tr> -<tr><td class="tar pr05">13.</td><td class="tal">Sertularia operculata</td><td class="tar prl05 bl">33.</td><td class="tal">Comatula, early stage of Starfish</td></tr> -<tr><td class="tar pr05">14.</td><td class="tal">Sponge, Grantia</td><td class="tar prl05 bl">34.</td><td class="tal">Carbonate of Lime, artificial</td></tr> -<tr><td class="tar pr05">15.</td><td class="tal">Sertularia operculata, with ovicells</td><td class="tar prl05 bl">35.</td><td class="tal">Sea Urchin, transverse section of spine</td></tr> -<tr><td class="tar pr05">16.</td><td class="tal">Actinia, showing weapons</td><td class="tar prl05 bl">36.</td><td class="tal">Serpula, bundle of spears</td></tr> -<tr><td class="tar pr05">17.</td><td class="tal"> Do. base of weapon more magnified </td><td class="tar prl05 bl">37.</td><td class="tal">Sun-star, part of skin</td></tr> -<tr><td class="tar pr05">18.</td><td class="tal">Sponge granule, ciliated</td><td class="tar prl05 bl">38.</td><td class="tal">Oyster shell in different stages</td></tr> -<tr><td class="tar pr05">19.</td><td class="tal">Anguinaria anguina</td><td class="tar prl05 bl">39.</td><td class="tal">Cilia on mussel</td></tr> -<tr><td class="tar pr05">20.</td><td class="tal">Spicules of sponge from Oyster Shell </td><td class="tar prl05 bl"></td><td class="tal"></td></tr> -</table></div> - -<div class="figcenter" style="width: 435px;"> -<a id="Pl_IX"></a> -<img src="images/i_p_009.jpg" width="435" height="700" alt="" /> -<div class="caption"><p>IX.</p></div> -</div> - -<p><span class="pagenum" title="129"><a name="Page_129" id="Page_129"></a></span></p> - -<p>In shape, those of the mammalia are circular -discs, mostly with a concave centre, though the -camel has oval ones; those of the birds are more -or less oval and convex; those of the reptiles are -decidedly oval, very thin, and have the nucleus -projecting; and those of the fishes are oval and -mostly convex. During the process of coagulation -the blood corpuscles run together into a series of -rows, just as if a heap of pence had been piled on -each other and then pushed down, so that each -penny overlaps its next neighbour.</p> - -<p>These objects are illustrated by six examples on -Plate X. Fig. <a href="#Pl_X">2</a> is human blood, showing one of -the white corpuscles; Fig. <a href="#Pl_X">3</a> is the blood of the -pigeon; Fig. <a href="#Pl_X">4</a>, of the <i>Proteus anguínus</i>; Fig. <a href="#Pl_X">5</a>, of -the tortoise; Fig. <a href="#Pl_X">6</a>, of the frog, showing the projecting -nucleus; and Fig. <a href="#Pl_X">7</a>, of the roach. The -blood possesses many curious properties, which cannot -be described in these few and simple pages.</p> - -<p>In the centre of Plate <a href="#Pl_X">X</a>. is a large circular figure -representing the membrane of a frog’s foot as seen -through the microscope, and exhibiting the circulation -of the blood. The mode of arranging the foot -so as to exhibit the object without hurting the frog -is simple enough.</p> - -<p>Take an oblong slip of wood,—my own was made -in five minutes out of the top of a cigar-box,—bore a<span class="pagenum" title="130"><a name="Page_130" id="Page_130"></a></span> -hole about an inch in diameter near one end, and -cut a number of little slits all round the edge of the -wooden slip. Then get a small linen bag, put the -frog into it, and dip him into water to keep him -comfortable. When he is wanted, pull one of his -hind feet out of the bag, draw the neck tight -enough to prevent him from pulling his foot back -again, but not sufficiently tight to stop the circulation. -Have a tape fastened to the end of the bag, -and tie it down to the wooden slide. Then fasten -a thread to each of his toes, bring the foot well over -the centre of the hole, stretch the toes well apart, -and keep them in their places by hitching the -threads into the notches on the edge of the wooden -strip. Perhaps an easier plan is to secure the -threads by drops of sealing-wax when in the desired -position. Push a glass slide carefully between the -foot and the wood, so as to let the membrane rest -upon the glass, and be careful to keep it well wetted. -If the frog kick, as he will most likely do, pass a -thin tape over the middle of the leg, and tie him -gently down to the slide.</p> - -<p>Bring the glass into focus, and the foot will -present the appearance so well depicted in the -engraving. The veins and arteries are seen spreading -over the whole of the membrane, the larger -arteries being often accompanied by a nerve, as seen -in the illustration. Through all these channels the -blood continually pours with a rather irregular -motion, caused most probably by the peculiar -position of the reptile. It is a most wonderful -sight, of which the observer is never tired, and<span class="pagenum" title="131"><a name="Page_131" id="Page_131"></a></span> -which seems almost more interesting every time -that it is beheld.</p> - -<p>The corpuscles go pushing and jostling one -another in the oddest fashion, just like a British -crowd entering an exhibition, each one seeming to -be elbowing its way to the best place. To see them -turning the corners is very amusing, for they always -seem as if they never could get round the smaller -vessels, and yet invariably accomplish the task with -perfect ease, turning about and steering themselves -as if possessed of volition, and insinuating their -ends when they could not pass crosswise.</p> - -<p>By putting various substances, such as spirit or -salt, upon the foot, the rapidity of the circulation -at the spot can be greatly increased or reduced at -will, or even stopped altogether for a while, and the -phenomenon of inflammation and its gradual natural -cure be beautifully illustrated. The numerous black -spots upon the surface are pigment-cells.</p> - -<p>The tails of young fish also afford excellent objects -under the microscope, as the circulation can be seen -nearly as well as in the frog’s foot. The gills of -tadpoles can also be arranged upon the stage with -a little care, and the same organs in the young of the -common newt will also exhibit the circulation in a -favourable manner. The frog, however, is perhaps -the best, as it can be arranged on the “frog-plate” -without difficulty, and the creature may be kept for -months by placing it in a cool, damp spot, and -feeding it with flies, little slugs, and similar -creatures.</p> - -<hr class="chap" /> - -<div class="chapter"> -<p><span class="pagenum" title="132"><a name="Page_132" id="Page_132"></a></span></p> - - - - -<h2>CHAPTER VIII</h2> -</div> - -<p class="tac">Pond-Life—Apparatus and Instructions for Collecting Objects—Methods -of Examination—Sponge—Infusoria.</p> - - -<p>Of all departments of microscopic research the -most fascinating and the most popular is that -which deals with what is known by the generic -name of “pond-life.” The minute forms of the -animal creation included in this term are of such -exquisite beauty, and allow the processes of their -life-history to be followed with such facility, from -the cradle (when they have one) to the grave -(which is very often the body of another, larger, -organism), that there is none which has attracted -more observers. Indeed, the first application of -the microscope, by Leeuwenhoek, early in the -seventeenth century, was to the observation of -these forms of life.</p> - - -<p class="tac">X.</p> - -<div class="center"> -<table border="0" cellpadding="0" cellspacing="0" summary="Key to Plate X"> -<tr><td class="tar pr05 fs70">FIG.</td></tr> -<tr><td class="tar pr05">1.</td><td class="tal">Skin, Frog</td><td class="tar prl05 bl">18.</td><td class="tal"> Do.  Wild Duck</td></tr> -<tr><td class="tar pr05">2.</td><td class="tal">Blood, Human</td><td class="tar prl05 bl">19.</td><td class="tal">Circulation of blood, Frog’s foot</td></tr> -<tr><td class="tar pr05">3.</td><td class="tal"> Do.  Pigeon</td><td class="tar prl05 bl">20.</td><td class="tal">Feather, Sparrow</td></tr> -<tr><td class="tar pr05">4.</td><td class="tal"> Do.  Proteus</td><td class="tar prl05 bl">21.</td><td class="tal"> Do.  Cock’s tail</td></tr> -<tr><td class="tar pr05">5.</td><td class="tal"> Do.  Tortoise</td><td class="tar prl05 bl">22.</td><td class="tal">Fibre, crystalline lens of fish</td></tr> -<tr><td class="tar pr05">6.</td><td class="tal"> Do.  Frog</td><td class="tar prl05 bl">23.</td><td class="tal">Nerve</td></tr> -<tr><td class="tar pr05">7.</td><td class="tal"> Do.  Fish</td><td class="tar prl05 bl">24.</td><td class="tal">Muscle, Meat</td></tr> -<tr><td class="tar pr05">8.</td><td class="tal">Human nail</td><td class="tar prl05 bl">25.</td><td class="tal">Tooth, transverse section</td></tr> -<tr><td class="tar pr05">9.</td><td class="tal">Bone, Human</td><td class="tar prl05 bl">26.</td><td class="tal"> Do.  Longitudinal section</td></tr> -<tr><td class="tar pr05">10.</td><td class="tal">White fibrous tissue</td><td class="tar prl05 bl">27.</td><td class="tal">Sweat duct</td></tr> -<tr><td class="tar pr05">11.</td><td class="tal">Epithelial cells from tongue </td><td class="tar prl05 bl">28.</td><td class="tal">Eye of Haddock</td></tr> -<tr><td class="tar pr05">12.</td><td class="tal">Feather, Peacock</td><td class="tar prl05 bl">29.</td><td class="tal">Myliobates, palate</td></tr> -<tr><td class="tar pr05">13.</td><td class="tal">Spine, Hedgehog, transverse section </td><td class="tar prl05 bl">30.</td><td class="tal">Gristle, Pig</td></tr> -<tr><td class="tar pr05">14.</td><td class="tal">Pax-wax</td><td class="tar prl05 bl">31.</td><td class="tal">Pigment, Human eye</td></tr> -<tr><td class="tar pr05">15.</td><td class="tal">Epithelial cells from nose</td><td class="tar prl05 bl">32.</td><td class="tal"> Do.  Wing of Bat</td></tr> -<tr><td class="tar pr05">16.</td><td class="tal">Bone, Ostrich</td><td class="tar prl05 bl">33.</td><td class="tal"> Do.  Shell of Prawn</td></tr> -<tr><td class="tar pr05">17.</td><td class="tal">Feather, Shaft of Canary’s</td><td class="tar prl05 bl"></td><td class="tal"></td></tr> -</table></div> - -<div class="figcenter" style="width: 437px;"> -<a id="Pl_X"></a> -<img src="images/i_p_010.jpg" width="437" height="700" alt="" /> -<div class="caption"><p>X.</p></div> -</div> - -<p><span class="pagenum" title="133"><a name="Page_133" id="Page_133"></a></span></p> - -<p>A few words may be said, in the first place, as -to the outfit. A very useful part of it is a walking-stick, -to which can be attached either a net for -capturing the larger forms of life, or a hook for -collecting the weeds, to which many forms of great -interest and beauty are attached (Fig. <a href="#Fig_15">15</a>). The -stick is telescopic, and can also have attached to it -a bottle, which, put into the water at any desired -spot,—say, amongst a clump of weeds, or near the -bottom, upside down, and then suddenly reversed,—will -bring away samples of the inhabitants of -the neighbourhood. When these are sparsely distributed -through the water, the latter may be concentrated -by the use of a bottle round the neck of -which is firmly tied a coarse calico bag, funnel-shaped, -and supported by a wire ring, somewhat as -shown in the illustration. Muslin is, however, too -coarse for many organisms. This net is immersed -in the water so that the ring is just above the -surface, and one bottleful after another poured -through. The water strains off, the organisms are -left behind. The immersion is necessary to reduce -the pressure to which delicate organisms would -otherwise be subjected. When the bottle is full, -or sufficiently concentrated as to its contents, the -latter are poured into one of the ordinary collecting-bottles, -of which half a dozen at least should -always be taken.</p> - -<div class="figcenter" style="width: 430px;"> -<a id="Fig_15"></a> -<img src="images/i_133.jpg" width="430" height="242" alt="" /> -<div class="caption"><p><span class="smcap">Fig. 15.</span></p></div> -</div> - -<p><span class="pagenum" title="134"><a name="Page_134" id="Page_134"></a></span></p> - -<p>On reaching home, and as often as possible on -the way, the corks should be removed, as these -organisms soon use up the air in the water.</p> - -<p>For examination a glass trough of considerable -size, say three inches in length, half an inch in -depth, and two inches in height, should be half -filled with the water, and examined with the pocket -magnifier. With a little practice it will be found -easy to take up not only the larger organisms, but -even very minute ones, with one of the dipping-tubes -with a long tapering point already referred -to. The organism, when “spotted,” is followed by -eye and tube, the finger being held over the mouth -of the latter, and at the critical moment the finger -is removed, and the organism swept into the tube -by the in-rushing water. Now wipe off the excess -with a clean handkerchief, “spot” the organism in -the tube again, and carefully absorb the superfluous -water with a piece of blotting paper; and -finally, gently but sharply blow the remainder on -to the plate of the live-box, put on the cover, and -examine with a one-inch power. If, as often -happens, the organism sticks to the side of the -tube, a little more water must be drawn in, and -the process repeated. The use of the cotton-wool -trap spoken of previously will often be very helpful -in the examination of actively moving organisms.</p> - -<p>In the case of weeds, a small portion should be -placed in the trough and carefully examined from -end to end, first with the pocket lens and then -with the one-inch power. Let us now consider -the objects most likely to be met with.</p> - -<p><span class="pagenum" title="135"><a name="Page_135" id="Page_135"></a></span></p> - -<p>A piece of stick may be coated with a white -layer, feeling rough to the touch, and full of small -holes. The chances are that this will be a piece -of fresh-water sponge, <i>Spongilla fluviatílis</i>, and by -dark-field illumination particles may be seen to -enter at some orifices and be ejected at others. -With a very high power and a very thin section, -properly prepared, these holes will be seen to be -the mouths of channels which are lined by the most -delicate organisms possible, each having a minute -body crowned with a tiny crystal cup, in the -middle of which is a long cilium, or flagellum, as it -is here called (Plate XIII. Fig. <a href="#Pl_XIII">1</a>). The currents -are produced by the combined action of these -flagella. In point of fact, the sponge is a colony -of minute animals working harmoniously for the -common good. If the specimen be found in winter -the sponge will be full of tiny balls, the “gemmules” -of the next season’s growth. The roughness -is due to the flinty spicules, which are at once the -scaffolding and the protection of the sponge, and -by boiling the sponge in a mixture of nitric acid -and water (half and half) these spicules will be set -free, and may be washed, allowed to settle, washed -again, dried, and mounted in balsam. The gemmules -are coated by very beautiful spicules, consisting -of two wheels connected by a rod. These -may be treated in the same way. The life-history -of the common sponge is as yet but imperfectly -known.</p> - -<p>Perhaps the lowest form of life is the <i>Amœba</i>, -shown in Plate IX. Fig. <a href="#Pl_IX">1</a>, a mere lump of jelly,<span class="pagenum" title="136"><a name="Page_136" id="Page_136"></a></span> -which flows along, and when it comes into contact -with any likely subject for digestion flows round -it, encloses it, absorbs what it can from it, and -leaves it behind. A near relative of the Amœba -is the <i>Arcella</i> (Fig. <a href="#Pl_IX">2</a>), which is simply an Amœba -with a shell. Being unable to swim, these organisms -are naturally to be most often found at the bottom -of the collecting bottle, and it is always advisable -to take up a portion of the débris with a dipping -tube, which is then held upright on a slide with -the finger upon it until the dirt settles on to the -slide, when it is removed, a cover-glass put upon -the dirt, and a quarter-inch power used for -examination. Many forms will be discovered -in this way which would otherwise escape -observation.</p> - -<p>Another curious organism, of great size (comparatively) -and extreme beauty, is the sun animalcule -(<i>Actínophrys</i>), which has a round body and -long tentacles (Fig. <a href="#Pl_IX">3</a>), to which free-swimming -organisms adhere, and by the combined action of -the neighbouring ones are drawn to the body and -received into it; one cannot say swallowed.</p> - -<p>Fig. <a href="#Pl_IX">6</a>, Plate IX., shows the curious arithmetical -process whereby the Infusoria multiply by -division, a groove appearing at one point, rapidly -deepening, and finally separating the animal completely -into two. The species is the <i>Chílodon</i>, a -flattened creature, ciliated all over, having a set of -teeth arranged in the form of a tube, and at its -fore-part a kind of membranous lip. A similar -phenomenon, in an earlier stage, is shown in<span class="pagenum" title="137"><a name="Page_137" id="Page_137"></a></span> -Fig. <a href="#Pl_XIII">26</a>, Plate XIII., the organism in this case being -<i>Euplótes</i>.</p> - -<p>It has been said that sponges are colonies of -extremely minute organisms, each furnished with a -membranous collar or funnel, the whole looking -like an exquisite wine-glass without a foot. These -organisms are not always grouped in colonies, however. -Many are free-growing, and may be found -attached to the stems of water-plants, but they are -extremely minute, and will hardly be noticed until -the microscopist has acquired considerable experience, -nor even then—with such an instrument -as we have postulated—will he see more than a -tiny pear, with a straight line, the margin of the -cup, on each side of its summit. The flagellum -will be quite invisible.</p> - -<p>Some similar organisms may, nevertheless, be -found which, though still minute, are within the -range of a properly managed quarter-inch objective. -Such an one, of extreme beauty, is the <i>Dinobrýon</i> -shown in Plate XIII. Fig. <a href="#Pl_XIII">3</a>. Each “zoöid,” as -the separate animals are called, among the Infusoria, -or each generation of zoöids, stands upon its parent -and has two flagella. When alarmed, the zoöid -sinks to the bottom of its cell, and withdraws its -flagella. In Fig. <a href="#Pl_XIII">2</a> (<i>Eugléna</i>) we have a similar -zoöid, but of far greater size, and free-swimming. -It is a very common object, and possesses a red -eye-speck close to the “contractile vesicle.” All -Infusoria have the latter, some a great number, as -in Fig. <a href="#Pl_XIII">9</a>. The vesicle contracts at regular intervals, -and is then simply blotted out, but reforms<span class="pagenum" title="138"><a name="Page_138" id="Page_138"></a></span> -in the same place, so that it is probably the heart -or the urinary bladder of these minute animals.</p> - -<p>The lovely rosette shown in Fig. <a href="#Pl_XIII">4</a> is the <i>Synura</i>, -a spherical colony of zoöids, each of which has -two flagella, and is in addition clothed with rows -of cilia. A beautiful sight it is to watch these -colonies rolling through the field of view. Not -uncommon, especially in brackish water, is the -<i>Peridinium</i> (Fig. <a href="#Pl_XIII">5</a>), with its plate armour, long -flagellum, and girdle of cilia. A gigantic species -of the same family is common in sea-water, and -will be easily recognised by its body, not much -larger than that of Peridinium, being furnished -with three long arms, curiously bent. It is called -<i>Ceratium</i>, and is sometimes present in such abundance -as to thicken the water, near the surface of -which it swims.</p> - -<p>We now come to a class of Infusoria which is -characterised by the possession of a complete -covering of cilia, arranged in rows all over the -body. The number of these is enormous; we can -only glance at a few types, by mastering which the -observer will, at all events, know whereabouts he -is. The first we will take is the <i>Coleps</i> (Fig. <a href="#Pl_XIII">6</a>), a -very common kind, whose body is marked by a -series of geometrical lines, so that the organism -looks very much like an elongated geographical -globe. These markings are on the tunic, which is -of a brownish colour. Very different is the <i>Trachelocerca</i> -(Fig. <a href="#Pl_XIII">7</a>), with its long flexible neck, which -is in constant movement from side to side as the -creature swims along. As seen in the figure, the<span class="pagenum" title="139"><a name="Page_139" id="Page_139"></a></span> -neck is clear and the head has a fringe of longer -cilia.</p> - -<p>The <i>Trachelius</i> (Fig. <a href="#Pl_XIII">8</a>) is perhaps the largest of -all the Infusoria, being readily visible to even an -inexperienced eye. Its body is richly furnished -with contractile vesicles, and the protoplasm is -curiously reticulated. We may here remark that -the Trachelius is especially prompt in doing what -most of these organisms do when put under pressure -in a live-box, namely, in performing a kind of <i>harakiri</i>. -The outline first becomes irregular, then the -body rapidly swells and finally comes to pieces, the -fragments dancing mockingly away under the influence -of their still-moving cilia. The remedy is to -use the cotton-wool trap and the lightest possible -pressure.</p> - -<p>A very elegant organism is shown in the bottom -right-hand corner of the Plate (Fig. <a href="#Pl_XIII">25</a>). It is the -<i>Loxophyllum</i>, and has a strongly marked contractile -vesicle.</p> - -<p>Another large form is <i>Amphileptus</i> (Fig. <a href="#Pl_XIII">9</a>), -already referred to as having a large number of -contractile vesicles arranged in a regular row; -and more massive still is <i>Bursaria</i> (Fig. <a href="#Pl_XIII">10</a>), a very -curious organism, very much like a purse indeed, -and possessing a wonderful arrangement of cilia -inside the funnel. These are arranged like a ladder, -a series of rows of short stiff cilia, which move at -short intervals in unison, and tend to sweep down -into the cavity any small particles of food. This -arrangement is here described for the first time, -and appears to be quite unlike anything else among<span class="pagenum" title="140"><a name="Page_140" id="Page_140"></a></span> -the Infusoria. Not unlike Bursaria, but having no -ladder, and being furnished with a delicate membranous -pouch in front of the slit of the purse, is -<i>Condylostoma</i>, which we shrewdly suspect to be the -young form of Bursaria. This is a point which -requires elucidation.</p> - -<p>One of the most beautiful of all these forms is -shown in Fig. <a href="#Pl_XIII">11</a>, <i>Folliculina</i>, a type of a large -group characterised by the possession of a transparent -case, of extremely elegant form, within which -the animal retreats on the slightest alarm.</p> - -<p>Fearless and independent, as becomes its size, is -the trumpet-shaped <i>Stentor</i> (Fig. <a href="#Pl_XIII">12</a>), which may -easily be seen when present, as it is in almost -every good gathering of water-weed. The particular -form drawn (<i>S. Mülleri</i>) does not make a case, -but many members of the genus do, and it is very -common to see a stem almost covered with them. -Such a sight, once seen under dark-field illumination, -will never be forgotten. The method of multiplication -of the Stentors (by division) is extremely -easy to watch, and very instructive.</p> - -<p>A curious organism is <i>Trichodina</i> (Fig. <a href="#Pl_XIII">13</a>), which, -though a free-swimmer, is always parasitic upon -the body of some higher animal. We have found -it sometimes upon Hydra, and always in hundreds -upon the stickleback. The next group of Infusoria -is distinguished by the body’s being only ciliated at -particular points, usually round the mouth, or what -acts as such. The first form is Vorticella (Fig. <a href="#Pl_XIII">14</a>), -a beautiful vase-like creature upon a stem. Down -the stem runs a muscular fibre, and on the least -shock the fibre contracts and draws the stem into -a beautiful spiral, whilst the cilia are drawn in, -and the zoöid assumes the appearance of a ball at -the end of a watch-spring. An exquisite sight is -a colony of Vorticellæ, for these actions are always -going on, as, for example, when one member of the -family touches another, which is quite sufficient to -provoke the contraction.</p> - - -<p class="tac">XI.</p> - -<p class="tac">POLARIZED LIGHT.</p> - -<div class="center"> -<table border="0" cellpadding="0" cellspacing="0" summary="Key to Plate XI"> -<tr><td class="tar pr05 fs70">FIG.</td></tr> -<tr><td class="tar pr05">1.</td><td class="tal">Carbonate of Lime</td><td class="tar prl05 bl">16.</td><td class="tal">Chlorate of Potash, Crystals</td></tr> -<tr><td class="tar pr05">2.</td><td class="tal">Starfish</td><td class="tar prl05 bl">17.</td><td class="tal">Cellularia reptans</td></tr> -<tr><td class="tar pr05">3.</td><td class="tal">Thistle down</td><td class="tar prl05 bl">18.</td><td class="tal">Star-shaped hair, Stalk of Yellow Water-Lily</td></tr> -<tr><td class="tar pr05">4.</td><td class="tal">Starch, Wheat</td><td class="tar prl05 bl">19.</td><td class="tal">Teeth, Palate of Whelk</td></tr> -<tr><td class="tar pr05">5.</td><td class="tal"> Do.  Potato</td><td class="tar prl05 bl">20.</td><td class="tal">Zoophyte, Bowerbankia</td></tr> -<tr><td class="tar pr05">6.</td><td class="tal">Prawn-shell</td><td class="tar prl05 bl">21.</td><td class="tal">Raphides, <i>i.e.</i> crystalline formations in</td></tr> -<tr><td class="tar pr05">7.</td><td class="tal">Starch, “Tous les mois” </td><td class="tar prl05 bl"></td><td class="tal">  vegetable cells, Bulb of Hyacinth</td></tr> -<tr><td class="tar pr05">8.</td><td class="tal">Bone, cancellous</td><td class="tar prl05 bl">22.</td><td class="tal"> Do.  Rhubarb</td></tr> -<tr><td class="tar pr05">9.</td><td class="tal">Gun-cotton</td><td class="tar prl05 bl">23.</td><td class="tal">Sulphate of Magnesia, Crystals</td></tr> -<tr><td class="tar pr05">10.</td><td class="tal">Cow’s hair</td><td class="tar prl05 bl">24.</td><td class="tal">Bone, Skate</td></tr> -<tr><td class="tar pr05">11.</td><td class="tal">Hoof, donkey, longitudinal </td><td class="tar prl05 bl">25.</td><td class="tal">Cherrystone, transverse section</td></tr> -<tr><td class="tar pr05">12.</td><td class="tal"> Do.  transverse</td><td class="tar prl05 bl">26.</td><td class="tal">Sugar, Crystals in honey</td></tr> -<tr><td class="tar pr05">13.</td><td class="tal">Nitre, Crystals</td><td class="tar prl05 bl">27.</td><td class="tal">Tendon, Ox</td></tr> -<tr><td class="tar pr05">14.</td><td class="tal">Scale, Eel</td><td class="tar prl05 bl">28.</td><td class="tal">Calcareous plates. Tooth of Echinus</td></tr> -<tr><td class="tar pr05">15.</td><td class="tal">Wing, Water-Boatman</td><td class="tar prl05 bl"></td><td class="tal"></td></tr> -</table></div> - -<div class="figcenter" style="width: 437px;"> -<a id="Pl_XI"></a> -<img src="images/i_p_011.jpg" width="437" height="700" alt="" /> -<div class="caption"><p>XI.</p></div> -</div> - -<p><span class="pagenum" title="141"><a name="Page_141" id="Page_141"></a></span></p> - -<p>Many compound tree-like forms of Vorticella are -known, one of which, <i>Carchesium</i> (Fig. <a href="#Pl_XIII">15</a>), may -serve as a type of all. In the case of this organism, -the colony contracts in sections on a moderate -shock; in the second, <i>Zoothamnium</i>, as a whole; -whilst in <i>Epistylis</i> the stalks are rigid, and the -individuals contract singly. When the shock is -violent, the appearance presented by the two former -is that shown in Fig. <a href="#Pl_XIII">16</a>. In all three cases the -colonies are usually so large that they are visible -as trees to the naked eye, and some members of -the group are extremely common. Moreover, they -are often parasitic, as, for example, upon Cyclops, -which is frequently loaded with them.</p> - -<p>Another compound form is <i>Ophrydium</i>, a colony -of which (not unusually large) is shown of the -natural size in Fig. <a href="#Pl_XIII">18</a>, with a single zoöid, magnified, -by the side of it, in Fig. <a href="#Pl_XIII">19</a>.</p> - -<p>Lastly, we have an exquisite group of organisms -related to Vorticella, but possessing a transparent -envelope, the forms of which are most varied, but -always graceful. <i>Vaginicola</i> (Fig. <a href="#Pl_XIII">17</a>) is a good -example of this, and <i>Cothurnia</i> (Fig. <a href="#Pl_XIII">20</a>) still -more so. Many of these organisms, too, are furnished<span class="pagenum" title="142"><a name="Page_142" id="Page_142"></a></span> -with a plate, attached either to the head or -to the body, which plate, when they withdraw into -their cases, closes the latter perfectly, as in the case -of the exquisite <i>Pyxicola</i> (Fig. <a href="#Pl_XIII">21</a>).</p> - -<p>A very interesting but singularly obtrusive -organism is the <i>Stylonychia</i> (Figs. <a href="#Pl_XIII">22</a>, 23). How -often has it happened to us to have an interesting -object nicely in the field of view, and then to have -it knocked out of sight by the blundering incursion -of this burly fellow, who runs so rapidly by means -of his “styles” that he gives nothing time to get -out of the way. He is of interest to us, however, -as the representative of a class in which the body -is not ciliated, or very partially and slightly so, -usually round the mouth. We have frequently -found Stylonychia, in company with Vorticella and -<i>Paramœcium</i> (Plate IX. Fig. <a href="#Pl_IX">6</a>), in the water in -which flowers have been standing for a few days; -sometimes the numbers are so great as to make the -water quite milky.</p> - -<p>One more form must conclude this short sketch -of the great Infusorial family. It is the <i>Acineta</i> -(Fig. <a href="#Pl_XIII">24</a>), which, attached by its foot-stalk, and -devoid of cilia, patiently waits, with outspread arms, -to receive and embrace smaller members of the -family as they dance merrily about. Alas! its -embrace is as fatal as that of the image of the -Virgin which bore beneath its robe spikes and -daggers, for the victim struggles vainly to escape, -and the nourishment from its body is rapidly -absorbed.</p> - -<p>And here we take our leave of a group which,<span class="pagenum" title="143"><a name="Page_143" id="Page_143"></a></span> -simple as is the construction of the animals which -it includes (for every one, great and small alike, is -composed of a single cell), is yet full of beauty and -interest. He who wishes to pursue the matter -further will find in Saville Kent’s <i>Manual of the -Infusoria</i> a perfect mine of information, to which -we gladly acknowledge our indebtedness, both now -and in time past.</p> - -<hr class="chap" /> - -<div class="chapter"> -<p><span class="pagenum" title="144"><a name="Page_144" id="Page_144"></a></span></p> - - - - -<h2>CHAPTER IX</h2> -</div> - -<p class="tac">Fresh-water Worms—Planarians—Hydra—Polyzoa—Rotifers—Chætonotus—Water-Bears.</p> - - -<p>The fresh-water worms form a large and well-defined -group, and a few words regarding them -may be useful.</p> - -<p>They are very common, and very difficult to -find information about, most of the work relating -to them having been done in Germany. At the -same time, they are so highly organised and so -transparent that the process of their life-history -may be easily followed.</p> - -<p>One large group has the peculiarity of multiplying -by division, the last joints or segments -being devoted to the formation of the new individual. -At one time of the year the ordinary -sexual process of reproduction takes the place of -this method, and each worm is then surrounded by -a belt such as may be seen in the common earthworm -under similar conditions. Further information -on this subject is greatly needed.</p> - -<p>The type is the common <i>Naïs</i>, which has a body -of thirty segments or more, two eye-specks on the -head, and a double row of bristles along the back; -whilst below, each segment carries strong hooked<span class="pagenum" title="145"><a name="Page_145" id="Page_145"></a></span> -bristles, nearly buried in the body, by means of -which the worm crawls. Inside the mouth is a -large proboscis, which can be protruded, and this -leads into a stomach which is merely an enlargement -of the intestine which succeeds it. The -circulation of the blood (which is colourless) can -be easily watched. It begins at the tail with a -contraction of the dorsal vessel, passes up to the -head, and then down below the intestine to the -tail again. The intestine is ciliated inside, and it -is by a current of water carried into the intestine -by these cilia that the blood is aërated.</p> - -<p>In the next genus, <i>Dero</i>, this is clearly seen, for -the tail (Plate XIV. Fig. <a href="#Pl_XIV">1</a>) is opened out into a -wide shield, from which rise four, six, or even eight -finger-like processes. These parts are all ciliated, -and contain a network of blood-vessels. The worm -lives in a case which it builds in the mud, and the -way to find it is to put some of the mud into a -glass beaker with water, and allow it to stand. -If there be members of this family in it, their tails -will be seen protruding above the water. Pour out -the mud sharply, fill up with water, and allow the -dirt to subside, and the worms may then be made -to leave their cases by pressure by a camel hair -pencil on the lower end of the tube, and may be -caught with the dipping tube and placed in the -live-box. They have no eyes, otherwise the general -outline of the body closely resembles that of Naïs.</p> - -<p><i>Slavína</i> (Fig. <a href="#Pl_XIV">2</a>) has a row of touch-organs, like -pimples, round each segment, and is a dirty looking -creature, with an inordinately long first pair of<span class="pagenum" title="146"><a name="Page_146" id="Page_146"></a></span> -bristles, but this reaches its acme in <i>Pristina</i> (Fig. <a href="#Pl_XIV">3</a>) -(sometimes, though wrongly, called <i>Stylaria</i>) -<i>parasita</i>, which has three long sets of bristles upon -the back, and keeps these in constant wing-like -motion. The true <i>Stylaria</i> has a long trunk, set -right in the head, and tubular (Fig. <a href="#Pl_XIV">6</a>); it grows -to a considerable length, and when in the stage of -fission it is very funny to see the two proboscides -waving about, one on the middle, as well as the -original one at the head. There is also a form -with a shorter proboscis of the same kind.</p> - -<p><i>Bohemilla</i> has a tremendous array of saw-like -bristles upon the back, whilst <i>Chætogaster</i> has none -at all in this position, and few below. <i>Æolosoma</i> -has merely tufts of hair instead of bristles, and -swims freely. It is easily recognised by the red, -yellow, or green pigment spots in its skin, and by -the ciliated head. Rarest of all the family is the -one which connects it with the ordinary <i>Tubifex</i>, -the red worm which lives in masses in the mud of -brooks and ponds, the waving tails protruding above -the water, and being instantly withdrawn when a -foot is stamped upon the bank. Their Naid cousin -is <i>Naidium</i>, and has red blood, but multiplies by -fission, which Tubifex does not.</p> - -<p>Another group of worms is the <i>Planarians</i>, small -leech-like worms, black, white, or brown, which are -rarely absent from a gathering. The would-be -investigator will find in them an abundant field for -work, as they are but very imperfectly known or -studied.</p> - -<p>The great enemy of all these worms is the<span class="pagenum" title="147"><a name="Page_147" id="Page_147"></a></span> -<i>Hydra</i>, a good idea of which may be formed from -Plate IX. Fig. <a href="#Pl_IX">13</a>. There are three species, all -of which are fairly common. They capture their -prey in exactly the same way as sea-anemones and -the marine hydroid forms, so numerous and varied.</p> - -<p>Nor must we omit to notice the exquisitely beautiful -Polyzoa, such as <i>Lophopus</i> (Plate XIV. Fig. <a href="#Pl_XIV">4</a>), -with its ciliated tentacles and transparent social -home; <i>Fredericella</i> (Fig. <a href="#Pl_XIV">5</a>), with its graceful stems, -and their still more graceful inhabitants; and the -wonderful <i>Cristatella</i>, whose colonies form bodies -which crawl over the stems of water plants. -But for grace, beauty, and variety, the Rotifers -assuredly outshine all their fellow inhabitants of -our ponds and streams.</p> - -<p>We can only take a few types, and of all these -the most common is the common Rotifer (Plate IX. -Fig. <a href="#Pl_IX">10</a>). It is there shown in the act of swimming, -but it can withdraw its “wheels” and creep -like a leech, protruding its foot as it does so. It is -distinguished by the two eye-spots on the proboscis -from <i>Philodina</i>, in which they are on the breast, -and <i>Callidina</i>, which has none. When at ease in -its mind, the animal protrudes its wheels, and by -their action draws in particles of food, these passing -down to the incessantly moving jaws, which act -like a mill and crush the food before it passes on to -be digested. The movement of the jaws may even -be seen in the young Rotifer whilst still in the egg -within the body of the parent, and as the egg -reaches its full development other eggs again -are visible within it, so that we may have three<span class="pagenum" title="148"><a name="Page_148" id="Page_148"></a></span> -generations in one individual. The males of most -of the Rotifera are unknown. Those that are -known are very lowly organised, having only the -ciliary wreath and the reproductive organs, and -are only found at certain seasons of the year. For -the remainder of the time parthenogenesis is the -rule, just as among the Aphides. We select a few -individuals for illustration as types. Those who -wish to pursue this study further must be referred -to the monumental work of Hudson and Gosse.</p> - -<p>The common Rotifer, already referred to, may be -taken as the type of the Bdelloida, or leech-like -class, so called from their mode of “looping” themselves -along. The group is a comparatively small -one in comparison with the next, the Ploïma, or -free-swimmers. We can only select from the vast -variety a few species, first of those classed as -illoricated, from their being without a <i>loríca</i>, or -case, and then of the loricated, which possess it. -A very large and common form is <i>Hydátina</i> (Plate XIV. -Fig. <a href="#Pl_XIV">7</a>), which lives by choice in the reddish -pools of water found often by the roadside. It -shows the whole organisation of the class magnificently; -the ciliary wreath on the head, with the -striped muscles which draw the latter back, the -powerful jaws, the digestive canal with its crop and -intestine, the ovary with the developing eggs, the -water-vascular system with the curious vibratile -tags, and finally, the cloaca, which receives the -waste of the body and expels it at intervals.</p> - -<p>Another form, also common, especially in clear -water, is <i>Synchæta</i> (Fig. <a href="#Pl_XIV">8</a>), very much like a kite<span class="pagenum" title="149"><a name="Page_149" id="Page_149"></a></span> -or peg-top in shape, which has the power of attaching -itself by a glutinous thread, and spinning round -at a tremendous rate. Then there is the gigantic -<i>Asplanchna</i> (Fig. <a href="#Pl_XIV">9</a>), which has no opening below, -so that the waste must be discharged by the mouth; -and curious <i>Sacculus</i>, which gorges itself with -chlorophyll until it looks like a green bag with a -string round it, but clear and sparkling. Of the -<i>Notommatæ</i> there is a whole host, but we can only -mention the beautiful <i>N. Aurita</i> (Fig. <a href="#Pl_XIV">10</a>), with an -eye of a beautiful violet colour, composed of several -spherules massed together, and two curious ear-like -processes on the head, from which it takes its -name. Some of the Ploïma have powers of leaping -which must be noticed. The <i>Triarthra</i> (Fig. <a href="#Pl_XIV">11</a>) -has three arms, or what we may call such, which -it can stretch out suddenly and leap to a considerable -distance, whilst in <i>Polyarthra</i> the arms become -a whole cluster of broad saw-like bristles.</p> - -<p>We pass on to note a few species of the mail-clad -or loricated Rotifers, chief among which the -great <i>Euchlanis</i> (Fig. <a href="#Pl_XIV">12</a>), a noble-looking fellow, -calls for our attention, his great size rendering him -easily visible to the naked eye. It is difficult to -avoid using the masculine gender, but, of course, all -those figured and described are of the gentler sex. -<i>Salpina</i>, too (Fig. <a href="#Pl_XIV">14</a>), with its box-like lorica, armed -with spines at each of the upper angles, and having -three below, is quite easily recognised, and very -common. <i>Brachionus</i> (Fig. <a href="#Pl_XIV">13</a>) has a shield-shaped -case, well furnished with spines, symmetrically -arranged at the top, and an opening below for the<span class="pagenum" title="150"><a name="Page_150" id="Page_150"></a></span> -flexible wrinkled tail, like the trunk of an elephant. -<i>Pterodina</i> (Fig. <a href="#Pl_XIV">15</a>) has a similar tail, but a round -case, and the head is much more like that of the -common Rotifer when extended. <i>Anuræa</i> (Fig. <a href="#Pl_XIV">16</a>), -on the other hand, has no tail, and its case is shaped -like a butcher’s tray, with a handle at each corner. -<i>Dinocharis</i> (Fig. <a href="#Pl_XIV">17</a>) has a roof-like case, with long -spines on the root of the tail, and a forked stiff -foot. <i>Noteus</i> (Fig. <a href="#Pl_XIV">18</a>) is much like Pterodina, -except in its foot, which more nearly resembles -that of Dinocharis.</p> - -<p>The list might be indefinitely extended, but -sufficient has probably been said to enable the tyro -to find his bearings in this large, beautiful, and -interesting class.</p> - -<p>We pass on to notice in conclusion two or three -of the fixed forms, of which a beautiful example is -the <i>Melicerta ringens</i> (Plate IX. Fig. <a href="#Pl_IX">7</a>), whose building -operations have a never-ending charm. Particles -of débris are accumulated in a curious little -cavity in the chin, in which they are whirled round, -and mixed with a secretion which binds them -together, and when a brick is made the head is -bent down and the brick applied to the desired -spot with mathematical regularity. By supplying -fine particles of innocuous colouring matters, the -Melicerta may be made to build a variegated case. -The most remarkable specimen known is the one -figured in Hudson and Gosse’s work, which was -found by the present writer in a specimen of water -from which he had already obtained five-and-twenty -species of various kinds of Rotifer; the water was<span class="pagenum" title="151"><a name="Page_151" id="Page_151"></a></span> -collected by an inexperienced person, and there was -only a pint of it. It had, moreover, been kept for -three weeks, and the moral of that is, to preserve -one’s gatherings, and keep an aquarium into which -they may be poured when done with for the -moment. New forms will often develop with -startling rapidity, their eggs having been present in -the original gathering. The young form of Melicerta, -shown in Plate XIV. Fig. <a href="#Pl_XIV">20</a>, is strangely -unlike its mother, and much more nearly resembles -its father.</p> - -<p>Another group of extreme beauty is the Flosculariæ -(Fig. <a href="#Pl_XIV">19</a>), several species of which are very -common. They will be easily known by their -appearance, which resembles a shaving brush when -closed; whilst, when opening, the shaving brush -resembles a cloud of delicate shimmering threads, -which at last stand out straight, radiating all round -the head of the creature, and forming the trap by -means of which it catches its prey. Finally, there -is the lovely <i>Stephanoceros</i> (not, unfortunately, very -common), with its five symmetrically placed and -gracefully curved arms, perhaps the most lovely of -all Rotifers, with its exquisitely transparent body, -sparkling with masses of green and golden brown. -He who finds this has a treasure indeed, and will -be encouraged to prosecute his studies in this -“Fairyland of Microscopy.”</p> - -<p>Two irregular forms call for a word of remark. -The first is <i>Chætonotus</i> (Plate XIII. Fig. <a href="#Pl_XIII">27</a>), which -stands on the borderland of the Infusoria and the -Rotifers, neglected as a rule by the students of both;<span class="pagenum" title="152"><a name="Page_152" id="Page_152"></a></span> -and the second the <i>Tardigrada</i> (Plate XIV. -Fig. <a href="#Pl_XIV">21</a>), or water-bears, which have feet like those of -the red wriggling larva of <i>Chironomus</i>, whose silky -tubes are common enough on submerged walls and -on the stems of plants, these feet consisting of a -mass of radially arranged hooklets, which can be -protruded or withdrawn at will; whilst the head of -the water-bear is far more like that of a louse, -pointed and hard, and suited for burrowing about, -as the animal does, among the rubbish at the -bottom of the bottle. Both the genera just referred -to will repay careful study, as little is -known of their life-history or development.</p> - -<p>A few words must be devoted, in conclusion, to -the Entomostraca, those shrimp-like animals which, -like their marine relatives, act as scavengers to -the community. Fig. <a href="#Pl_XIV">22</a> is a portrait of <i>Cypris</i>, a -not very handsome form, but one very commonly -found. Its shell is opaque, so that the internal -organs are difficult to observe. Far different in -this respect is the beautiful <i>Daphnia</i>, the water-flea -<i>par excellence</i>, whose carapace is of crystalline -clearness, so that every movement of every one -of the internal organs may be followed with the -greatest facility. There are many species of the -genus, and some of them are very common, so that -the opportunity of examining these lovely objects -is easily obtained. Plate XIV. Fig. <a href="#Pl_XIV">23</a>, shows the -most common of all the class under notice, the -<i>Cyclops</i>, so named from the fact that, like the fabled -giants of classical literature, it has a single eye in -the middle of its forehead. It is often loaded with -Infusoria, especially Vorticella and Epistylis, already -described, to such an extent that its movements -are greatly hampered.</p> - - -<p class="tac">XII.</p> - -<div class="center"> -<table border="0" cellpadding="0" cellspacing="0" summary="Key to Plate XI"> -<tr><td class="tar pr05 fs70">FIG.</td></tr> -<tr><td class="tar pr05">1.</td><td class="tal">Tubercle, Sun-star</td><td class="tar prl05 bl">14.</td><td class="tal"> Do.  Truncatulina</td></tr> -<tr><td class="tar pr05">2.</td><td class="tal">Zoophyte, Gemellaria</td><td class="tar prl05 bl">15.</td><td class="tal"> Do.  Polymorphina</td></tr> -<tr><td class="tar pr05">3.</td><td class="tal">Cuttle bone</td><td class="tar prl05 bl">16.</td><td class="tal"> Do.  Miliolina</td></tr> -<tr><td class="tar pr05">4.</td><td class="tal">Plate of ditto from above</td><td class="tar prl05 bl">17.</td><td class="tal">Gold dust, with quartz</td></tr> -<tr><td class="tar pr05">5.</td><td class="tal">Zoophyte, Antennularia</td><td class="tar prl05 bl">18.</td><td class="tal">Foraminifer, Lagena vulgaris</td></tr> -<tr><td class="tar pr05">6.</td><td class="tal">Pedicellaria, skin of Starfish </td><td class="tar prl05 bl">19.</td><td class="tal">Pouches, Skin of Rat’s tail</td></tr> -<tr><td class="tar pr05">7.</td><td class="tal">Shell, Foraminifer</td><td class="tar prl05 bl">20.</td><td class="tal">Foraminifer, Biloculina ringens</td></tr> -<tr><td class="tar pr05">8.</td><td class="tal">Snake-star, disc from below </td><td class="tar prl05 bl">21.</td><td class="tal">Ore, Copper</td></tr> -<tr><td class="tar pr05">9.</td><td class="tal">Pedicellaria, Echinus</td><td class="tar prl05 bl">22.</td><td class="tal">Zoophyte, Membranipora pilosa</td></tr> -<tr><td class="tar pr05">10.</td><td class="tal">Wing-case, Weevil</td><td class="tar prl05 bl">23.</td><td class="tal">Human skin, injected</td></tr> -<tr><td class="tar pr05">11.</td><td class="tal">Coralline</td><td class="tar prl05 bl">24.</td><td class="tal">Coal, Longitudinal section</td></tr> -<tr><td class="tar pr05">12.</td><td class="tal">Spine, Echinus</td><td class="tar prl05 bl">25.</td><td class="tal"> Do.  Transverse section</td></tr> -<tr><td class="tar pr05">13.</td><td class="tal">Foraminifer, Polystomella </td><td class="tar prl05 bl">26.</td><td class="tal">Lung, Frog</td></tr> -</table></div> - -<div class="figcenter" style="width: 437px;"> -<a id="Pl_XII"></a> -<img src="images/i_p_012.jpg" width="437" height="700" alt="" /> -<div class="caption"><p>XII.</p></div> -</div> - -<p><span class="pagenum" title="153"><a name="Page_153" id="Page_153"></a></span></p> - -<p>We have not space to figure more of these -creatures, but other forms will be found not inferior -in interest to those mentioned. The most -curious of all are those which earn a dishonest and -lazy living by attaching themselves to the bodies of -other and larger animals, chiefly fish. One of the -largest is the <i>Argulus</i>, the bane of aquarium -keepers, which is of considerable size, and attacks -gold-fish, and in fact almost any fish to which it -can obtain access.</p> - -<p>The gills of the stickleback will furnish examples -of the curious <i>Ergasilus</i>, which consists chiefly of -an enormous pair of hooks and two long egg-bags, -the latter, in varying form, being carried by many -of the Entomostraca.</p> - -<p>Upon the fins of the same fish will be found the -remarkable <i>Gyrodactylus</i>, a worm-like animal which -attaches itself by a large umbrella-like foot, in the -centre of which are two huge claws. The head is -split down the middle for some distance. We may -mention, in concluding our notice of the external -and involuntary guests of the unlucky stickleback, -that its skin is usually frequented by hosts of the -Trichodina described in the last chapter. Of the -internal parasites, want of space forbids us to -speak.</p> - -<hr class="chap" /> - -<div class="chapter"> -<p><span class="pagenum" title="154"><a name="Page_154" id="Page_154"></a></span></p> - - - - -<h2>CHAPTER X</h2> -</div> - -<p class="subhead">Marine Life—Sponges—Infusoria—Foraminifera—Radiolaria—Hydroid -Zoophytes—Polyzoa—Worms—Lingual Ribbons -and Gills of Mollusca—Star-Fishes and Sea-Urchins—Cuttle-Fish— -Corallines—Miscellaneous Objects.</p> - - -<p>Great as is the range of objects presented to the -student of fresh-water life, the latter field is limited -indeed as compared with that afforded by the sea. -The Infusoria and Rotifers furnished by the latter -are, indeed, much fewer in number and variety, -but the vast host of sponges, polyzoa, hydroids, -crustacea, molluscs, ascidians, and worms, to say -nothing of the wealth of vegetable life, renders -the sea the happy hunting-ground of the microscopist.</p> - -<p>Whether it be along the edge of the water, as -the tide retreats, especially after a gale; or in the -rock-pools; or, perhaps best of all, upon those -portions of the shore left uncovered only by the -lowest spring-tides, the harvest is simply inexhaustible. -Stones turned up will exhibit a world -in miniature. Encrusted with green or pink -sponges, or with gelatinous masses of ascidians, -fringed at its edges with hydroids, coated above -with polyzoa, a single one will often supply more<span class="pagenum" title="155"><a name="Page_155" id="Page_155"></a></span> -work than could be got through in a week of -steady application.</p> - -<p>A description of the fresh-water sponge already -given may serve very well to indicate the general -outlines of the organisation of the marine ones too. -The spicules of the latter are, however, not always -flinty; very often, as in the case of <i>Grantia</i> (Plate IX. -Figs. <a href="#Pl_IX">8</a> and 14), they are calcareous, a point -which can be settled by the application of a little -nitric acid and water. If lime be present there -will be strong effervescence, and the separation of -the spicules can only be effected by gently warming -a portion of the sponge in caustic potash -solution, pouring the resulting mass into water, -and allowing the spicules to settle. The washing -and settling must be repeated several times, and a -portion of the deposit may then be taken up with -a dipping-tube, spread upon a slide and dried, and -then covered in balsam solution. The forms are -endless, and the same sponge will often supply -three or four, or even more. Among them may -be seen accurate likenesses of pins, needles, marlin-spikes, -cucumbers, grappling-hooks, fish-hooks, -porters’-hooks, calthrops, knife-rests, fish-spears, -barbed arrows, spiked globes, war-clubs, boomerangs, -life-preservers, and many other indescribable forms. -The flinty forms must be prepared by boiling, as -described in speaking of the mounting of diatoms -in Chapter XI., except that, of course, only one -settlement is required after thorough washing.</p> - -<p>Every one who has been by or on the sea on a -fine summer night must have noticed the bright<span class="pagenum" title="156"><a name="Page_156" id="Page_156"></a></span> -flashes of light that appear whenever its surface is -disturbed; the wake of a boat, for example, leaving -a luminous track as far as the eye can reach. This -phosphorescence is caused by many animals resident -in the sea, but chiefly by the little creature represented -at Fig. <a href="#Pl_IX">9</a>, the <i>Noctilúca</i>, myriads of which -may be found in a pail of water dipped at random -from the glowing waves. A tooth of this creature -more magnified is shown immediately above.</p> - -<p>A large group of microscopic organisms is known -to zoologists under the name of Foraminifera, on -account of the numerous holes in their beautiful -shells, most of which are composed of carbonate -of lime, though some are horny and others are -composed of aggregations of minute grains of sand, -the forms in one class often closely imitating those -in another. It is of the shells of these minute -animals that the “white cliffs of old England” are -very largely composed, and those who desire to -understand the part which these tiny creatures -have played, and are playing, in geology, will do -well to study Huxley’s fascinating essay on “A -Piece of Chalk.”</p> - - -<p class="tac">XIII.</p> - -<div class="center"> -<table border="0" cellpadding="0" cellspacing="0" summary="Key to Plate XIII"> -<tr><td class="tar pr05 fs70">FIG.</td></tr> -<tr><td class="tar pr05">1.</td><td class="tal">Grantia compressa</td><td class="tar prl05 bl">14.</td><td class="tal">Vorticella nebulifera</td></tr> -<tr><td class="tar pr05">2.</td><td class="tal">Euglena viridis</td><td class="tar prl05 bl">15.</td><td class="tal">Zoothamnium arbuscula</td></tr> -<tr><td class="tar pr05">3.</td><td class="tal">Dinobryon sertularia </td><td class="tar prl05 bl">16.</td><td class="tal"> Do.  do.  contracted</td></tr> -<tr><td class="tar pr05">4.</td><td class="tal">Synura uvella</td><td class="tar prl05 bl">17.</td><td class="tal">Vaginicola crystallina</td></tr> -<tr><td class="tar pr05">5.</td><td class="tal">Peridinium tabulatum </td><td class="tar prl05 bl">18.</td><td class="tal">Ophrydium versatile (colony)</td></tr> -<tr><td class="tar pr05">6.</td><td class="tal">Coleps hirtus</td><td class="tar prl05 bl">19.</td><td class="tal"> Do.  do.  (single zoöid)</td></tr> -<tr><td class="tar pr05">7.</td><td class="tal">Trachelocerca viridis </td><td class="tar prl05 bl">20.</td><td class="tal">Cothurnia imberbis</td></tr> -<tr><td class="tar pr05">8.</td><td class="tal">Trachelius ovum</td><td class="tar prl05 bl">21.</td><td class="tal">Pyxicola affinis</td></tr> -<tr><td class="tar pr05">9.</td><td class="tal">Amphileptus gigas</td><td class="tar prl05 bl">22–23.</td><td class="tal">Stylonychia mytilus</td></tr> -<tr><td class="tar pr05">10.</td><td class="tal">Bursaria Mülleri</td><td class="tar prl05 bl">24.</td><td class="tal">Acineta grandis</td></tr> -<tr><td class="tar pr05">11.</td><td class="tal">Folliculina elegans</td><td class="tar prl05 bl">25.</td><td class="tal">Loxophyllum meleagris</td></tr> -<tr><td class="tar pr05">12.</td><td class="tal">Stentor polymorphus </td><td class="tar prl05 bl">26.</td><td class="tal">Euplotes charon (dividing)</td></tr> -<tr><td class="tar pr05">13.</td><td class="tal">Trichodina pediculus </td><td class="tar prl05 bl">27.</td><td class="tal">Chætonotus larus</td></tr> -</table></div> - -<div class="figcenter" style="width: 476px;"> -<a id="Pl_XIII"></a> -<img src="images/i_p_013.jpg" width="476" height="700" alt="" /> -<div class="caption"><p>XIII.</p> -</div> -</div> - -<p><span class="pagenum" title="157"><a name="Page_157" id="Page_157"></a></span></p> - -<p>The inhabitants of these shells are Amœbæ, -mere masses of jelly, and some forms may be -found sliding over the weeds in almost every rock-pool. -The anchor-mud, already spoken of, always -contains some, and many forms may be found in -the sand from sponges, which should be passed -through a series of wire sieves, of increasing -fineness, and the residuum in each case be examined -dry under a one-inch power. The shells -may be picked up with a needle which has been -slightly greased by being passed over the hair, and -they may be mounted by sticking them to the -slide with thin starch paste, putting on a cover-glass -properly supported, and then running -turpentine under the cover-glass, heating to expel -the air, and finally filling up with balsam. Or, as -opaque objects, they may be mounted in a cell -dry. The forms are endless, but all are beautiful, -and a few examples are given in Plate IX. Fig. <a href="#Pl_IX">4</a> -(<i>Miliolína</i>), and Plate XII. Fig. <a href="#Pl_XII">7</a>, which is a -portion of the shell to show the holes, Fig. <a href="#Pl_XII">13</a> -(<i>Polystomella</i>), Fig. <a href="#Pl_XII">14</a> (<i>Truncatulína</i>), Fig. <a href="#Pl_XII">15</a> -(<i>Polymorphína</i>), Fig. <a href="#Pl_XII">16</a> (<i>Miliolína</i>, partly fossilised), -Fig. <a href="#Pl_XII">18</a> (<i>Lagéna</i>). and Fig. <a href="#Pl_XII">20</a> (<i>Biloculína</i>).</p> - -<p>Allied to these are the lovely Radiolaria, whose -shells, constructed on a similar plan, are composed -of flint. They are found in remarkable profusion -in the deposit from Cambridge, Barbados, but also -in a living state at even enormous depths in the -ocean. The present writer has obtained many -forms from <i>Challenger</i> soundings, and the great -authority on this subject is Haeckel’s report in the -official accounts of the expedition of the above-named -vessel.</p> - -<p>The Hydroid Zoophytes are represented by -several examples. These creatures are soft and -almost gelatinous, and are furnished with tentacles -or lobes by which they can catch and retain their -prey. In order to support their tender structure -they are endowed with a horny skeleton, sometimes -outside and sometimes inside them, which is called<span class="pagenum" title="158"><a name="Page_158" id="Page_158"></a></span> -the polypidom. They are very common on our -coasts, where they may be found thrown on the -shore, or may be dredged up from the deeper -portions of the sea.</p> - -<p>Fig. <a href="#Pl_IX">13</a> is a portion of one of the commonest -genera, <i>Sertularia</i>, showing one of the inhabitants -projecting its tentacles from its domicile. Fig. <a href="#Pl_IX">15</a> -is the same species, given to show the egg-cells. -This, as well as other zoophytes, is generally classed -among the sea-weeds in the shops that throng all -watering-places.</p> - -<p>The form just referred to is a near relative of -the Hydra, already described, and belongs to the -same great family as the sea-anemones. One form, -shown in Fig. <a href="#Pl_IX">26</a>, is the <i>Hydra Tuba</i>, long thought -to be a distinct animal, but now known to be the -young form of a jelly-fish, or Medusa. The Hydra -Tuba throws off joints at intervals, each of which -becomes a perfect jelly-fish. One of them is shown -in Fig. <a href="#Pl_IX">27</a>. Fig. <a href="#Pl_IX">28</a> represents a very small and -pretty Medusa, the Thaumantias. When this -animal is touched or startled, each of the purple -globules round the edge flashes into light, producing -a most beautiful and singular appearance. Fig. <a href="#Pl_IX">29</a> -exhibits the so-called compound eye of another -species of Medusa, though it would appear that -these are really connected with the nervous system -of the animal, and have to do with the pulsating -contractions of the bell by which it is propelled -through the water.</p> - -<p>In my <i>Common Objects of the Sea-Shore</i> the -Actíniæ, or Sea-Anemones, are treated of at some<span class="pagenum" title="159"><a name="Page_159" id="Page_159"></a></span> -length. At Fig. <a href="#Pl_IX">16</a> is shown part of a tentacle -flinging out the poison-darts by which it secures -its prey; and Fig. <a href="#Pl_IX">17</a> is a more magnified view of -one of these darts and its case.</p> - -<p>Much more might be said under this head, but -we must pass on to another group, which, whilst -possessing a certain general resemblance to the -hydroid zoophytes, differs utterly from them in -internal organisation. We have already referred -to the fresh-water polyzoa. The marine forms are -vastly more numerous, and more easily found, since -not only pieces of weed upon which they grow -are to be found upon every beach, but whole -masses of leaf-like colonies, forming what is known -as horn-wrack, may be plentifully found. Instead -of the tentacles armed with sting-cells, like the -anemone’s, possessed by the Hydrozoa, the Polyzoa -have arms clothed with active cilia, by which the -food is swept into the mouth, passing on into the -stomach, and then through the intestine to another -opening.</p> - -<p>Fig. <a href="#Pl_IX">19</a> is a very curious zoophyte called -<i>Anguinaria</i>, or snake-head, on account of its -shape, the end of the polypidom resembling the -head of the snake, and the tentacles looking like -its tongue as they are thrust forward and rapidly -withdrawn. Fig. <a href="#Pl_IX">21</a> is the same creature on an -enlarged scale, and just below is one of its -tentacles still more magnified. Fig. <a href="#Pl_IX">23</a> is the -ladies’-slipper zoophyte (<i>Eretea</i>); and Fig. <a href="#Pl_IX">24</a> is -called the tobacco-pipe or shepherd’s-purse zoophyte -(<i>Notamia</i>).</p> - -<p><span class="pagenum" title="160"><a name="Page_160" id="Page_160"></a></span></p> - -<p>Fig. <a href="#Pl_IX">22</a> is a portion of the <i>Bugula</i>, with one of -the curious “birds’-head” processes. These appendages -have the most absurd likeness to a bird’s -head, the beak opening and shutting with a smart -snap (so smart, indeed, that the ear instinctively -tries to catch the sound), and the head nodding -backward and forward just as if the bird were -pecking up its food. On Plate XII. Fig. <a href="#Pl_XII">2</a>, is a -pretty zoophyte called <i>Gemellaria</i>, on account of -the double or twin-like form of the cells; and -Fig. <a href="#Pl_XII">5</a> represents the <i>Antennularia</i>, so called on -account of its resemblance to the antennæ of an -insect. Fig. <a href="#Pl_XII">22</a> is an example of a pretty zoophyte -found parasitic on many sea-weeds, and known by -the name of <i>Membranipora</i>. Two more specimens -of zoophytes may be seen on Plate <a href="#Pl_XI">XI</a>. as they -appear under polarised light. Fig. <a href="#Pl_XI">17</a> is the -<i>Cellularia reptans</i>; and Fig. <a href="#Pl_XI">20</a> is the <i>Bowerbankia</i>, -one form of which occurs in fresh water.</p> - -<p>Among the worms we may refer to the beautiful -little <i>Spirorbis</i>, whose tiny coiled spiral tube may -be found attached to almost every sea-weed, and -which, when placed in a trough of sea-water, -protrudes its beautiful crown of plumes. In chalk -or other soft rocks, again, the tubes of <i>Spio</i>, with -its two long waving tentacles, may be found by -hundreds. Then there are the centipede-like -worms, which may be found under nearly every -stone, and which belong to the great family of -Nereids, provided with formidable jaws and stiff -bristles of various forms. The Serpulæ are allied -to the Spirorbis already mentioned. Parts of the<span class="pagenum" title="161"><a name="Page_161" id="Page_161"></a></span> -so-called feet of one of these worms are shown in -Fig. <a href="#Pl_IX">36</a>, where the spears or “pushing-poles” are -seen gathered into bundles, as during life. One -of them, on a larger scale, is shown in Fig. <a href="#Pl_IX">32</a>. -The gorgeous hairs of Aphrodite have already been -alluded to.</p> - -<p>In the sea the few species of Crustacea which -fresh water offers to the observer in the shape of -Cyclops and its allies become thousands, and their -changes during development are numerous and -puzzling. Who, for example, would suppose that -the young stage of the Cyclops was indistinguishable -in habits, and almost in form, from that of -the barnacle which adheres to the rocks? Yet -such is the case, and there are other metamorphoses -even more startling. Fig. <a href="#Pl_IX">25</a> is the larva -of the common crab, once thought to be a separate -species, and described as such under the name of -<i>Zoæa</i>.</p> - -<p>The Mollusca proper will not afford us many -objects, except in the form of their lingual ribbon, -which may be extracted from the mouth, gently -heated in <i>liquor potassæ</i>, and mounted in balsam -after well washing, when the rows of teeth form -splendid objects by polarised light. The palate of -a whelk is shown in Plate XI. Fig. <a href="#Pl_XI">19</a>.</p> - -<p>Again, the gills of the mussel will afford a -beautiful illustration of ciliary action. If a portion -of the thin plates which lie along the edge -of the shell be examined in a little of the liquor, -the action may be splendidly seen, and watched for -a long time (Fig. <a href="#Pl_IX">39</a>).</p> - -<p><span class="pagenum" title="162"><a name="Page_162" id="Page_162"></a></span></p> - -<p>The structure of shell, <i>e.g.</i> oyster-shell, is well -shown in three examples: Fig. <a href="#Pl_IX">34</a> is a group of -artificial crystals of carbonate of lime; and on -Figs. <a href="#Pl_IX">38</a> and 39 may be seen part of an oyster-shell, -showing how it is composed of similar -crystals aggregated together. Their appearance -under polarised light may be seen on Plate XI. -Figs. <a href="#Pl_XI">1</a> and 6.</p> - -<p>We now pass on to the Echinoderms, including -the star-fishes and sea-urchins.</p> - -<p>The old story of the goose-bearing tree is an -example of how truth may be stranger than fiction. -For if the fable had said that the mother goose -laid eggs which grew into trees, budded and -flowered, and then produced new geese, it would -not have been one whit a stranger tale than the -truth. Plate IX. Fig. <a href="#Pl_IX">33</a>, shows the young state -of one of the common star-fishes (<i>Comátula</i>), -which in its early days is like a plant with a -stalk, but afterwards breaks loose and becomes -the wandering sea-star which we all know so well. -In this process there is just the reverse of that -which characterises the barnacles and sponges, -where the young are at first free and then become -fixed for the remainder of their lives. Fig. <a href="#Pl_IX">30</a> is -the young of another kind of star-fish, the long-armed -Ophiúris, or snake-star.</p> - -<p>Fig. <a href="#Pl_IX">37</a> is a portion of the skin of the common -sun-star (<i>Solaster</i>), showing the single large spine -surrounded by a circle of smaller spines, supposed -to be organs of touch, together with two or three -of the curious appendages called pedicellariæ.<span class="pagenum" title="163"><a name="Page_163" id="Page_163"></a></span> -These are found on star-fishes and Echini, and -bear a close resemblance in many respects to the -bird-head appendages of the zoophytes. They are -fixed on foot-stalks, some very long and others -very short, and have jaws which open and shut -regularly. Their use is doubtful, unless it be to -act as police, and by their continual movements to -prevent the spores of algæ, or the young of various -marine animals, from effecting a lodgment on the -skin. A group, of pedicellariæ from a star-fish is -shown on a large scale on Plate XII. Fig. <a href="#Pl_XII">6</a>, and -Fig. <a href="#Pl_XII">9</a> of the same Plate shows the pedicellariæ of -the Echinus.</p> - -<p>Upon the exterior of the Echini, or sea-urchins, -are a vast number of spines having a very beautiful -structure, as may be seen by Fig. <a href="#Pl_IX">35</a>, Plate IX., -which is part of a transverse section of one of -these spines. An entire spine is shown on Plate XII. -Fig. <a href="#Pl_XII">12</a>, and shows the ball-and-socket joint -on which it moves, and the membranous muscle -that moves it. Fig. <a href="#Pl_XII">8</a> is the disc of the snake-star -as seen from below. Fig. <a href="#Pl_XII">1</a> is a portion of skin -of the sun-star, to show one of the curious -madrepore-like tubercles which are found upon -this common star-fish. Fig. <a href="#Pl_XII">3</a> is a portion of -cuttle “bone,” very slightly magnified, in order -to show the beautiful pillar-like form of its -structure; and Fig. <a href="#Pl_XII">4</a> is the same object seen -from above. When ground very thin this is a -magnificent object for the polariscope.</p> - -<p>One or two miscellaneous objects now come -before our notice. Fig. <a href="#Pl_XII">11</a> is one of those curious<span class="pagenum" title="164"><a name="Page_164" id="Page_164"></a></span> -marine plants, the Corallines, which are remarkable -for depositing a large amount of chalky matter -among their tissues, so as to leave a complete -cast in white chalk when the coloured living -portion of the plant dies. The species of this -example is <i>Jania rubens</i>.</p> - -<p>Fig. <a href="#Pl_XII">19</a> is part of the pouch-like inflation of the -skin, and the hairs found upon the rat’s tail, -which is a curious object as bearing so close a -similitude to Fig. <a href="#Pl_XII">22</a>, the sea-mat zoophyte. -Fig. <a href="#Pl_XII">23</a> is a portion of the skin taken from the -finger, which has been injected with a coloured -preparation in order to show the manner in which -the minute blood-vessels or “capillaries” are distributed; -and Fig. <a href="#Pl_XII">26</a> is a portion of a frog’s lung, -also injected.</p> - -<p>The process of injection is a rather difficult one, -and requires considerable anatomical knowledge. -The principle is simple enough, being merely to fill -the blood-vessels with a coloured substance, so as -to exhibit their form as they appear while distended -with blood during the life of the animal. It sometimes -happens that when an animal is killed -suddenly without effusion of blood, as is often seen -in the case of a mouse caught in a spring trap, -the minute vessels of the lungs and other organs -become so filled with coagulated blood as to form -what is called a natural injection, ready for the -microscope.</p> - -<p>Before leaving the subject I must ask the reader -to refer again for a moment to the frog’s foot on -Plate <a href="#Pl_X">X</a>., and to notice the arrangement of the dark<span class="pagenum" title="165"><a name="Page_165" id="Page_165"></a></span> -pigment spots. It is well known that when frogs -live in a clear sandy pond, well exposed to the rays -of the sun, their skins are bright yellow, and that -when their residence is in a shady locality, especially -if sheltered by heavy overhanging banks, they are -of a deep blackish-brown colour. Moreover, under -the influence of fear they will often change colour -instantaneously. The cause of this curious fact is -explained by the microscope.</p> - -<p>Under the effects of sunlight the pigment granules -are gathered together into small rounded spots, as -seen on the left hand of the figure, leaving the skin -of its own bright yellow hue. In the shade the -pigment granules spread themselves so as to cover -almost the entire skin and to produce the dark -brown colour. In the intermediate state they -assume the bold stellate form in which they are -shown on the right hand of the round spots. Very -remarkable forms of these cells may be found in -the skin of the cuttle-fish.</p> - -<p>Figs. <a href="#Pl_XII">24</a> and 25 are two examples of coal, the -former being a longitudinal and the latter a transverse -section, given in order to show its woody -character. Fig. <a href="#Pl_XII">17</a> is a specimen of gold-dust -intermixed with crystals of quartz sand, brought -from Australia; and Fig. <a href="#Pl_XII">21</a> is a small piece of -copper-ore.</p> - -<p>Every possessor of a microscope should, as soon -as he can afford it, add to his instrument the -beautiful apparatus for polarising light. The -optical explanation of this phenomenon is far too -abstruse for these pages, but the practical application<span class="pagenum" title="166"><a name="Page_166" id="Page_166"></a></span> -of the apparatus is very simple. It consists of two -prisms, one of which, called the polariser, is fastened -by a catch just below the stage; and the other, -called an analyser, is placed above the eye-piece. -In order to aid those bodies whose polarising -powers are but weak, a thin plate of selenite is -generally placed on the stage immediately below -the object. The colours exhibited by this instrument -are gorgeous in the extreme, as may be seen -by Plate <a href="#Pl_XI">XI</a>., which affords a most feeble representation -of the glowing tints exhibited by the -objects there depicted. The value of the polariser -is very great, as it often enables observers to distinguish, -by means of their different polarising -properties, one class of objects from another.</p> - -<p>If the expense of a polarising apparatus be too -great for the means of the microscopist, he may -manufacture a substitute for it by taking several -thin plates of glass, arranging them in a paper tube -so that the light may meet the surface of the -lowest one at an angle of about 52°, and placing -the bundle above the eye-piece to act as an analyser; -whilst, by using a plate of glass, and so arranging -the lamp that the light falls upon it at the above -angle, and is reflected up the tube of the microscope, -he will find on rotating the extemporised -analyser that the phenomena of polarisation are to -a great extent reproduced; whilst by splitting an -extremely thin film from the surface of a sheet of -mica, such as is employed for making smoke-screens -above glass globes, he will have a substitute for the -selenite by means of which alone can the gorgeous -effects be produced. The extemporised -apparatus will not, of course, give such perfect -effects, but this is sometimes an advantage, and -the present writer has used the same means with -considerable success in photographing starch-granules.</p> - - -<p class="tac">XIV.</p> - -<div class="center"> -<table border="0" cellpadding="0" cellspacing="0" summary="Key to Plate XIV"> -<tr><td class="tar pr05 fs70">FIG.</td></tr> -<tr><td class="tar pr05">1.</td><td class="tal">Dero latissima</td><td class="tar prl05 bl">13.</td><td class="tal">Brachionus amphiceros</td></tr> -<tr><td class="tar pr05">2.</td><td class="tal">Slavina serpentina</td><td class="tar prl05 bl">14.</td><td class="tal">Salpina mucronata</td></tr> -<tr><td class="tar pr05">3.</td><td class="tal">Pristina longiseta</td><td class="tar prl05 bl">15.</td><td class="tal">Pterodina patina</td></tr> -<tr><td class="tar pr05">4.</td><td class="tal">Lophopus crystallinus</td><td class="tar prl05 bl">16.</td><td class="tal">Anurœa brevispina</td></tr> -<tr><td class="tar pr05">5.</td><td class="tal">Fredericella sultana</td><td class="tar prl05 bl">17.</td><td class="tal">Dinocharis tetractis</td></tr> -<tr><td class="tar pr05">6.</td><td class="tal">Stylaria proboscidea (head) </td><td class="tar prl05 bl">18.</td><td class="tal">Noteus quadricornis</td></tr> -<tr><td class="tar pr05">7.</td><td class="tal">Hydatina senta</td><td class="tar prl05 bl">19.</td><td class="tal">Floscularia ornata</td></tr> -<tr><td class="tar pr05">8.</td><td class="tal">Synchœta mordax</td><td class="tar prl05 bl">20.</td><td class="tal">Young Melicerta</td></tr> -<tr><td class="tar pr05">9.</td><td class="tal">Asplanchna Brightwellii </td><td class="tar prl05 bl">21.</td><td class="tal">Macrobiotus (sp.?)</td></tr> -<tr><td class="tar pr05">10.</td><td class="tal">Notommata aurita</td><td class="tar prl05 bl">22.</td><td class="tal">Cypris fusca</td></tr> -<tr><td class="tar pr05">11.</td><td class="tal">Triarthra longiseta</td><td class="tar prl05 bl">23.</td><td class="tal">Cyclops quadricornis</td></tr> -<tr><td class="tar pr05">12.</td><td class="tal">Euchlanis triquetra</td><td class="tar prl05 bl"></td><td class="tal"></td></tr> -</table></div> - -<div class="figcenter" style="width: 426px;"> -<a id="Pl_XIV"></a> -<img src="images/i_p_014.jpg" width="426" height="700" alt="" /> -<div class="caption"><p>XIV.</p> -</div> -</div> - -<hr class="chap" /> - -<div class="chapter"> -<p><span class="pagenum" title="167"><a name="Page_167" id="Page_167"></a></span><span class="pagenum hide" title="168"><a name="Page_168" id="Page_168"></a></span></p> - - - - -<h2>CHAPTER XI</h2> -</div> - -<p class="subhead">Hints on the Preparation of Objects—Preservative Fluids—Mounting -Media—Treatment of Special Objects.</p> - - -<p>The microscopist who relies altogether on the dealer -for his permanent preparations may expend a good -deal of money, but the satisfaction which he derives -from his hobby will be very inferior to that experienced -by the worker who endeavours to secure, -for exhibition or for reference, specimens of the -objects which he finds most interesting and instructive -to himself.</p> - -<p>It will be our endeavour in the following pages -to give a summary of the elementary principles -upon which reliance is to be placed, though it -must be clearly understood that the technique of -the subject, already occupying a vast amount of -literature, is extending day by day, so that it is -impossible to deal exhaustively even with one -single section of it. Reference must be made, for -further information, to such publications as the -<i>Journal of the Royal Microscopical Society</i>, or that of -the Quekett Club, or to the monographs on the -various departments. Davies’ work on the general -subject will also be found useful by the beginner.</p> - -<p>Taking first the question of reagents, we may<span class="pagenum" title="169"><a name="Page_169" id="Page_169"></a></span> -mention five which leave the cells of a tissue as -nearly as possible in the natural condition, but fit -for permanent preservation. The first of these, in -order of importance and of general applicability, is -alcohol, represented for most purposes by methylated -spirit, which contains about 84 per cent. of -absolute alcohol, though, unfortunately for our purpose, -there is a certain quantity of mineral naphtha -in it in addition. This last has the effect of making -it go milky upon dilution with water, which is a -considerable disadvantage, though the milkiness -disappears to some extent on standing, and it is -rarely worth the while of the ordinary microscopist -to go through the formalities necessary to obtain -permission to purchase unmineralised spirit, which -cannot be had in quantities of less than five gallons -(as it is only to be had from the distillers under an -Excise permit), and distillers may not supply less.</p> - -<p>Four parts of methylated spirit with one of -water forms the classical “70 per cent.” alcohol, -the most generally useful of all fluids for hardening -and preserving purposes. A considerable quantity -of this fluid should always be available.</p> - -<p>Whatever other fluid may be used to begin with, -spirit must almost always be used to finish the -process, and fit the tissue for section-cutting and -staining.</p> - -<p>Of purely preservative, or fixative, fluids, we -may mention “formalin,” a 40 per cent. solution -of formic aldehyde, which is rapidly coming to the -front, as indeed it deserves to do. It is but slightly -poisonous, if at all, and leaves in the tissue nothing<span class="pagenum" title="170"><a name="Page_170" id="Page_170"></a></span> -which requires subsequent removal before proceeding -to harden for section-work, whilst it is an -admirable preservative of cell-form.</p> - -<p>Another admirable but highly poisonous reagent -is corrosive sublimate, in saturated solution, with -2 per cent. of acetic acid.</p> - -<p>A fourth is osmic acid, used in 1 per cent. -solution. This is a highly valuable reagent, but -extremely expensive, very poisonous, and giving off -fumes which are most irritating to the eyes.</p> - -<p>The fifth, a very gentle, but in many respects -very satisfactory one, is picric acid in saturated -solution. Tissues preserved in this medium must -not be washed out with water, as it enters into -very feeble combination with protoplasm, and the -cells swell and disintegrate as the reagent is dissolved -out.</p> - -<p>Of mounting media we may mention glycerine, -glycerine jelly (made by dissolving starch in glycerine -with the aid of heat), and Canada balsam, -dissolved in xylol or benzole. The Canada balsam -must be dried hard by evaporation over a water-bath, -and dissolved as wanted. Under no circumstances -should raw balsam be used, as it takes -years to set hard, and turns of a deep yellow colour -in the process.</p> - -<p>Chloroform is frequently used as a solvent, but -it has the disadvantage of attacking and extracting -a large number of the aniline dyes used for staining -structures, an objection from which the mineral -solvents are free.</p> - -<p>We will now proceed to go through the objects<span class="pagenum" title="171"><a name="Page_171" id="Page_171"></a></span> -already referred to, and indicate the method of -preservation.</p> - -<p>For the study of the cell-structures of plants the -portion to be examined is to be placed in spirit of -about 30 per cent. strength, which is changed after -twenty-four hours for 40 per cent., after a further -twenty-four hours for 55 per cent., and finally, as -regards our present purpose, in 70 per cent. spirit, -in which it may remain until required for section-cutting. -The effect of this treatment is to extract -the bulk of the water from the tissue, with the -minimum of shrinkage of the cells, the latter being -preserved in their natural relations to surrounding -parts.</p> - -<p>In some cases, however, it is desirable to examine -and preserve delicate structures, or parts, or dissections, -in a medium which allows of the retention -of the greater part of the natural moisture, and in -such a case the tissue is immersed in glycerine -diluted very much in the same way as the alcohol -in the last process, but with very much longer -intervals between the alterations of strength, until -it reaches pure glycerine, in which it remains for a -considerable time, as the exchange between the -tissue and the dense fluid surrounding it goes on -very slowly.</p> - -<p>A combination of the two methods is also possible, -the spirit-hardening being carried out for a portion -of the time, and the tissue being thereafter transferred -to glycerine, diluted or pure.</p> - -<p>The object of using glycerine at all is merely -that it has a much lower refractive index than<span class="pagenum" title="172"><a name="Page_172" id="Page_172"></a></span> -balsam, so that delicate structures may sometimes -be better seen in the former medium, but balsam -is to be preferred wherever it is possible to use it, -<i>i.e.</i> almost always. The writer has not mounted a -preparation in glycerine or a medium containing it -for many years, nor, with proper staining, does he -think it can ever be necessary to do so, except in -the case of dissections in which the glycerine can -be slowly run in without disturbing the arrangement, -as spirit would be pretty sure to do. The -harder portions of plants, woody stems, shells of -fruit, or the like, require different treatment, and -must, as a rule, be allowed to dry thoroughly before -being cut.</p> - -<p>Starch granules are somewhat troublesome to -mount satisfactorily. The writer has tried many -methods, and, on the whole, prefers a glycerin-gelatin -medium, which keeps for an almost indefinite -time, and may be made as follows: Thirty -grains of gelatine (Nelson’s “brilliant” or other -transparent gelatine is to be preferred) are allowed -to soak in water, and the swollen gelatine is -drained, and dissolved in the water which it has -absorbed, by the aid of a gentle heat. An equal -bulk of pure glycerine is then added. In using, a -small portion is transferred to a slide with the -point of a knife and melted, a small quantity of -starch granules added, and stirred into it with a -needle. The cover-glass is then laid up on the still-fluid -drop, pressed gently down so that the drop is -extended to the margin of the cover, and the whole -allowed to cool. It is then to be painted round with<span class="pagenum" title="173"><a name="Page_173" id="Page_173"></a></span> -several layers of Brunswick black, or Hollis’s glue, or -zinc-white cement, to prevent evaporation,—Hollis’s -glue being perhaps the best medium for the purpose.</p> - -<p>Petals, or other parts of which it is desired to -obtain a surface view, must be mounted in cells, -which may be made by the use of button-moulds -of suitable size, cemented to the glass slide with -marine glue. The slide must be free from grease, -as the tissue must be fixed in position by the use -of gum, and allowed to dry thoroughly before closing -the cell, or the cover-glass will be bedewed with -moisture when the cell is closed. The best plan is, -after air-drying for a couple of days, to place the -preparation on a metal plate over a beaker of boiling -water for an hour or more, and then to close -the cell immediately with Brunswick black, maintaining -the heat at first to ensure rapid drying, and -then slowly withdrawing it. When cool, another -coat should be given, and rather thick covers should -be used, as these preparations are never required to -be examined with high powers.</p> - -<p>To mount pollen-grains, they should be sprinkled -upon the surface of a slide which has been previously -moistened with thin gum, and allowed to -dry until it has become just “tacky”; the drying -is then completed by gentle heat and a drop of -balsam placed upon the grains, with a cover-glass -over all. Bubbles will probably form, but with -Canada balsam this is not of the slightest importance, -as they always come out of their own accord, -and balsam mounts should never be closed with -cement of any kind until thoroughly dry.</p> - -<p><span class="pagenum" title="174"><a name="Page_174" id="Page_174"></a></span></p> - -<p>Air-bubbles in other media may be eliminated -by the use of the air-pump shown in Fig. <a href="#Fig_16">16</a>, -which may be obtained from Baker at a very -reasonable rate, and which is useful not only for -that purpose, but for accelerating the drying of -moist tissues. To do this, there is placed upon the -plate of the pump a porcelain dish containing -strong sulphuric acid, and upon this is placed a -little triangle of platinum wire, which serves to -support the preparation. The air is now exhausted; -the tissue -parts with moisture -to supply its -place, and this -moisture is in turn -greedily absorbed -by the sulphuric -acid, so that drying -is rapid and -continuous, as well -as very thorough, -whilst the process has the great advantage of dispensing -entirely with the use of heat.</p> - -<div class="figcenter" style="width: 290px;"> -<a id="Fig_16"></a> -<img src="images/i_174.jpg" width="290" height="211" alt="" /> -<div class="caption"><p><span class="smcap">Fig. 16.</span></p></div> -</div> - -<p>Portions of many of the delicate algæ may be -mounted in glycerine, having previously been soaked -in it as already described; whilst the unicellular -forms, such as desmids and diatoms, may be preserved -in almost exactly the natural condition by -simply mounting them in a saturated solution of -picric acid.</p> - -<p>Probably formalin, in a solution of 10 per cent. -strength, would answer the purpose equally well,<span class="pagenum" title="175"><a name="Page_175" id="Page_175"></a></span> -but the writer has not tried it. It is hardly -necessary to say that, with such extremely fluid -media, great care is required in closing the cell. -A thin layer of Hollis’s glue should be first painted -on, to secure the cover in position, and when this -is thoroughly dry, several successive layers must -be added in the same way.</p> - -<p>It may be said here, that it is advisable in all -cases to use circular cover-glasses, as far as possible, -as they lend themselves with great facility to a -mechanically accurate closure. This slide is placed -upon a turn-table, carefully adjusted until the cover -is seen to be central when rotated, and a brush, -preferably a small camel-hair pencil, charged with -the desired fluid, but not in large excess, is held -against the junction of the slide and cover, whilst -the table is rapidly spun. A little experience will -teach better than any description what amount of -fluid there should be in the brush, and how thick -the cement should be. If too thick, it will drag off -the cover; if too thin, it will flow over the latter -and over the slide.</p> - -<p>The preparation of diatom-skeletons as permanent -objects is easy. Consisting, as they do, -of pure silex, or flint,—<i>i.e.</i>, practically glass,—they -resist long boiling in acids, so that there is little -difficulty in isolating them from any organic matter -with which they are mingled. It is generally -recommended to treat them with strong nitric -acid. This is a mistake. The acid acts much -more powerfully and less violently when diluted -with an equal bulk of water, and it is in an acid so<span class="pagenum" title="176"><a name="Page_176" id="Page_176"></a></span> -diluted that portions of water-plants, or other -diatomaceous material, should be boiled in a glass -beaker until all the organic matter is dissolved. -The beaker should be covered with a glass plate, -to prevent dissipation of the acid fumes. When -the process is complete, usually in about half an -hour, the contents of the beaker are thoroughly -stirred with a glass rod, poured rapidly off into a -larger bulk of cold water, and allowed to settle for -another half-hour. The process is then repeated -with a smaller bulk of water, several times, to -allow the removal of the last traces of acid, and -finally with distilled water. The separation of the -diatoms into grades is effected by settlement. The -final result is poured into a tall glass vessel, and -allowed to settle for, at first, a minute, the supernatant -fluid again poured off, and allowed to settle -for two minutes, and so on, the period being gradually -increased, and each sediment preserved apart. -The first will probably only be sand, but the proportion -of diatoms will increase with each separation, -though there will always be a certain proportion of -sand of such a size as to settle at the same rate -as the diatoms. Marine plants especially will -furnish a rich harvest by treatment as described.</p> - -<p>Solid diatomaceous deposits, such as kiesel-guhr, -mountain-meal, and especially the famous Oamaru -deposit from New Zealand, demand different treatment, -and perhaps the best way is to disintegrate -the mass, either by boiling with Sunlight soap -(though the alkali attacks the flint to some extent) -or to mix the mass with a super-saturated solution of<span class="pagenum" title="177"><a name="Page_177" id="Page_177"></a></span> -acetate of soda (made by saturating water with the -crystals whilst boiling), and by successive coolings, -heatings, and stirrings to cause the process of -crystallisation to break up the mass, which it -will do very thoroughly. The diatoms are then -separated by sedimentation, as above described.</p> - -<p>A small portion of the deposit may now be -spread thinly on a glass slide, allowed to dry -thoroughly, be treated with balsam, and covered.</p> - -<p>If it be desired to select individual diatoms, -this must be done under the microscope, by means -of a bristle fixed in a handle either with glue or -sealing-wax. The diatom selected will adhere to -the bristle if the latter be slightly greasy, and -should then be transferred to a slightly adhesive -slide, coated either with thin solution of white -shellac, or with thin gum nearly dry. When the -forms desired are mounted, the preparation should -be covered in balsam. The process is by no means -as easily effected as described, however.</p> - -<p>The preparation of insects, or parts of insects, as -microscopic objects is a tedious and difficult task. -The main point is the trouble of softening the -integument and eliminating the colour.</p> - -<p>The latter can, in any case, be only partially -effected. The beginner would do well to begin -with a fairly easy form, such as the worker-ant. -A good supply of these insects may be placed in a -bottle of liquor potassæ, and left there for at least -some days until they begin to become clear and -limp. From time to time a specimen may be -taken, well washed with several waters, then with<span class="pagenum" title="178"><a name="Page_178" id="Page_178"></a></span> -acetic acid and water of a strength of about 10 -per cent., then with weak spirit, about 50 per cent. -An attempt may then be made to arrange the -insect upon a slide, spreading out the legs so as -to exhibit them to the best advantage, and when -this has been done a cover-glass may be put on, -supported in such a way as to prevent absolute -pressure. The spirit is then withdrawn by means -of a piece of filtering-paper cut to a point, and -strong spirit added. This is again succeeded by -absolute alcohol, then by a mixture of turpentine -and crystal carbolic acid in equal proportions, and -finally the cover-glass is carefully lifted, and some -thick balsam solution dropped on, the limbs finally -arranged by means of warm needles, and the cover-glass -carefully replaced and pressed gently down -by means of a clip, which may be obtained for a -few pence. The whole is then set aside to harden, -the deficiency caused by evaporation made good, -the balsam allowed to dry, and the preparation -finally painted round.</p> - -<p>The contents of the body, in large insects, must -be removed, and this is effected during the washing -in water by gentle pressure with a camel-hair -brush, the process being aided, if necessary, by a -small incision made through the integument at the -root of the tail. Sections of insects require very -special methods, which will hardly fall within the -scope of this work.</p> - -<hr class="chap" /> - -<div class="chapter"> -<p><span class="pagenum" title="179"><a name="Page_179" id="Page_179"></a></span></p> - - - - -<h2>CHAPTER XII</h2> -</div> - -<p class="tac">Section-Cutting—Staining</p> - - -<p>No method of examination can equal, for general -applicability and usefulness, that of section-work. -The relations of the parts to each other being -preserved, it is possible to draw conclusions as to -their actual relations which no other mode allows -of, and we shall devote this concluding chapter to -some account of the methods to be employed to -this end.</p> - -<p>The apparatus required is not necessarily complicated. -Reduced to its elements, it consists -essentially only of a razor to cut the sections and -a dish to receive them. It but seldom happens, -however, that the relations of the parts in sufficiently -thin sections can be preserved by such a -rough-and-ready method, and frequently the object -to be cut is of such small dimensions as to render -it impossible to deal with it in this way. It is -therefore necessary to “imbed” it, so as to obtain -a handle by which to hold it, in such a way that -it shall be equally supported in all directions. -Moreover, since the human hand can only in exceptional -cases be brought to such a pitch of skill<span class="pagenum" title="180"><a name="Page_180" id="Page_180"></a></span> -as to cut a series of sections, or even single ones, -of the needful delicacy, some mechanical means -of raising the object through a definite distance -is highly desirable. The writer has cut many -thousands of sections with the “free hand,” but -the personal equation is a large one, and is not -always the same in the same person. For single -sections the method will, with practice, succeed -very well, but some means of securing a number -of sections of more or less the same thickness is -usually required.</p> - -<p>Let us deal with the imbedding first.</p> - -<p>If it be desired to imbed a tissue which has -merely been fixed with formalin, the block should -be immersed in strong gum (made by saturating -water with picked gum arabic, white and clean) -for several days. It is then taken out and, without -draining, transferred to the plate of a freezing -microtome, and the sections cut from the frozen -block, and mounted in glycerine at once.</p> - -<p>This plan is of limited usefulness, since it allows -of very little differentiation of the tissue elements, -and that only optical.</p> - -<p>To get the best results, some plan of staining -must be adopted. Perhaps the simplest, and certainly -a very excellent one, is as follows. After -the tissue has been passed from the hardening, or -fixing, fluid into the successive alcohols, as described, -it is placed in the following solution. Take about -forty grains of carmine and eighty grains of borax, -dissolve in about an ounce of water, add to the -mixture an ounce of methylated spirit, and let it<span class="pagenum" title="181"><a name="Page_181" id="Page_181"></a></span> -stand for some time with frequent shaking; about -a week will be sufficient, and the process of solution -may be hastened by gentle warming at intervals. -The clear upper portion is then poured off, and -into this the block of tissue is dropped, and allowed -to remain until thoroughly penetrated. Perhaps -the best plan is to substitute the carmine solution -for the 50 per cent. alcohol, and thus to make the -staining a stage in the hardening process. From -the carmine solution the tissue is transferred to -70 per cent. alcohol, to each ounce of which two -drops of hydrochloric acid have been added, and -after remaining in it for a day (with a piece of -the usual size) is placed in 70 per cent. alcohol, -in two successive quantities. Sections from this -material now only require treatment with the carbolic -acid and turpentine above mentioned to be -fit for mounting and covering in balsam. We now -proceed to indicate how the sections may be cut.</p> - -<p>A mixture of wax and almond oil, in proportions -varying with the heat of the weather, usually about -equal ones, is prepared. The piece of tissue is freed -from superfluous spirit by being placed on a bit of -blotting-paper for a minute or two, and is then -immersed in a quantity of the wax-and-oil mixture -contained in a little box of paper or lead-foil. The -tissue is held on the point of a needle, and lifted -up and down until it is coated with the mixture, -and, before solidification of the mass sets in, is -lowered into the box and left to cool. The block -now furnishes a handle, and this should be wrapped -round with paper, the sections cut with the keenest<span class="pagenum" title="182"><a name="Page_182" id="Page_182"></a></span> -possible razor, and as thin as possible, and placed -in spirit as cut. From the spirit, which must be -the strongest obtainable, they are placed in the -clearing liquid, carbolic and turpentine, and then -slid on to the slide, a drop of balsam placed on the -section, and the cover over all. Of late years all -sections of ordinary soft tissues, animal or vegetable, -have been cut by one of the infiltration methods, -in which the interstices of the tissue are filled up -by some material which prevents the relations of -the cells from being altered during the process of -cutting. To enter fully into this matter would -occupy too much space, and would serve no useful -purpose, for the worker who requires to make use -of such means will find it indispensable to obtain -Bolles Lee’s <i>Microtomist’s Vade Mecum</i>, in which -the whole matter is exhaustively treated.</p> - -<p>The simple method above detailed will answer -most ordinary purposes, provided that a few precautions -be attended to. The chief are as follows. -The outside of the block of tissue must be sufficiently -dry for the wax-and-oil to adhere to it. -The razor must be extremely sharp, and must be -kept so by application to a Turkey stone during the -section-cutting. The blade must be drawn across -the tissue from heel to point, and kept wetted with -spirit the whole time, so as to prevent any dragging -of the section. The transference of the section to -the slide must be effected by means of a section-lifter, -which may be made by beating out a piece -of stout copper wire to a thin flat blade; or a small -palette-knife, or German-silver lifter, may be purchased<span class="pagenum" title="183"><a name="Page_183" id="Page_183"></a></span> -for a few pence. The carbolic turpentine is -best used by placing a little in a watch-glass, and -floating the sections on to it by lifting them singly -with the lifter, freeing them from superfluous spirit -by draining on to blotting-paper, and allowing them -to float on to the surface of the liquid in the watch-glass, -so that the spirit may evaporate from above, -and be replaced by the clearing agent from below -The balsam solution should be thin, and the cover-glass -must be allowed to settle down into place -without pressure.</p> - -<p>The question of staining sections is a very large -one, and is becoming of daily increasing complexity.</p> - -<p>We cannot go into it here, further than to say -that most sections cut from unstained tissue will -yield excellent results if stained first with Delafield’s -logwood solution (to be obtained at Baker’s) to a very -slight extent, and then with a solution of safranin. -The sections should be washed with tap-water after -the logwood stain, and should be of a pale violet -colour. If over-stained, the colour may to a great -extent be removed by washing with a very weak -solution of hydrochloric acid, about two drops of -acid to each ounce of water, and repeated washing -in tap-water to remove the acid, and restore the -violet. The safranin stain should be weak, and -should be allowed to act for some time. From -this last the sections are transferred to strong -spirit, the latter being renewed until the sections -cease to give up the red dye; and they may then -be mounted as described. The results with most<span class="pagenum" title="184"><a name="Page_184" id="Page_184"></a></span> -tissues are superb, every detail of the structure -being splendidly brought out. Safranin alone is -also an admirable stain for many purposes.</p> - -<p>Further information must be sought in the book -already mentioned. Let us, in closing, warn the -beginner of two things which are of general application -in practical microscopy. The first is, not to -be discouraged by failures. The manipulations are -in many cases very delicate, and premiums must be -paid to experience for insurance against failure in -every one of the processes.</p> - -<p>The second is, that the most scrupulous cleanliness -will hardly suffice to prevent contamination -of preparation by the all-pervasive dust which, -invisible to the eye, assumes colossal proportions -under the microscope, and the particles of which -have an unpleasant habit of collecting on the most -interesting or most beautiful portion of the preparation. -This can only be guarded against by -careful filtration of all fluids, and constant watchfulness.</p> - -<p>A preparation properly made is a thing of beauty, -and a joy for ever,—or if not for ever, at any rate -for many years; and one such will repay an infinitude -of pains taken in its production.</p> - -<hr class="chap" /> - -<div class="chapter"> -<p><span class="pagenum" title="185"><a name="Page_185" id="Page_185"></a></span></p> - - - - -<h2>INDEX</h2> -</div> - -<hr class="r5" /> - - - -<div class="center"> -<table border="0" cellpadding="0" cellspacing="0" summary="Index"> -<tr><td></td><td class="tar pr1 fs80"><div>PAGE</div></td><td></td><td class="tar pr1 fs80"><div>PAGE</div></td></tr> -<tr><td class="tal">Air-pump,</td><td class="tar pr1"><div><a href="#Page_174">174</a></div></td><td class="tal pl15 bl">"   mounting of,</td><td class="tar pr1"><div><a href="#Page_177">177</a></div></td></tr> -<tr><td class="tal">Algæ,</td><td class="tar pr1"><div><a href="#Page_78">78</a></div></td><td class="tal pl05 bl"></td><td class="tar pr1"></td></tr> -<tr><td class="tal pl1">"  marine,</td><td class="tar pr1"><div><a href="#Page_92">92</a></div></td><td class="tal pl05 bl">Jelly-fish,</td><td class="tar pr1"><div><a href="#Page_158">158</a></div></td></tr> -<tr><td class="tal">Anemones, sea,</td><td class="tar pr1"><div><a href="#Page_159">159</a></div></td><td class="tal pl05 bl"></td><td class="tar pr1"></td></tr> -<tr><td class="tal">Antennæ,</td><td class="tar pr1"><div><a href="#Page_96">96</a></div></td><td class="tal pl05 bl">Larva of <i>Chironomus</i>,</td><td class="tar pr1"><div><a href="#Page_152">152</a></div></td></tr> -<tr><td class="tal">Ants,</td><td class="tar pr1"><div><a href="#Page_97">97</a></div></td><td class="tal pl05 bl">Light, arrangement of,</td><td class="tar pr1"><div><a href="#Page_29">29</a></div></td></tr> -<tr><td class="tal"></td><td class="tar pr1"></td><td class="tal pl05 bl">Live-box,</td><td class="tar pr1"><div><a href="#Page_17">17</a></div></td></tr> -<tr><td class="tal">Bacillaria,</td><td class="tar pr1"><div><a href="#Page_87">87</a></div></td><td class="tal pl05 bl">Logwood solution,</td><td class="tar pr1"><div><a href="#Page_183">183</a></div></td></tr> -<tr><td class="tal">Balancers of Fly,</td><td class="tar pr1"><div><a href="#Page_112">112</a></div></td><td class="tal pl05 bl"></td><td class="tar pr1"></td></tr> -<tr><td class="tal">Bark,</td><td class="tar pr1"><div><a href="#Page_61">61</a></div></td><td class="tal pl05 bl">Magnification, to measure,</td><td class="tar pr1"><div><a href="#Page_27">27</a></div></td></tr> -<tr><td class="tal">Blights,</td><td class="tar pr1"><div><a href="#Page_89">89</a></div></td><td class="tal pl05 bl">Mare’s tail,</td><td class="tar pr1"><div><a href="#Page_91">91</a></div></td></tr> -<tr><td class="tal">Blood, circulation of,</td><td class="tar pr1"><div><a href="#Page_129">129</a></div></td><td class="tal pl05 bl">Marine life,</td><td class="tar pr1"><div><a href="#Page_155">155</a></div></td></tr> -<tr><td class="tal pl1">"  corpuscles of,</td><td class="tar pr1"><div><a href="#Page_128">128</a></div></td><td class="tal pl05 bl">Microscope, Baker’s,</td><td class="tar pr1"><div><a href="#Page_14">14</a></div></td></tr> -<tr><td class="tal">Bone,</td><td class="tar pr1"><div><a href="#Page_123">123</a></div></td><td class="tal pl25 bl">"    "   “portable”, </td><td class="tar pr1"><div><a href="#Page_15">15</a></div></td></tr> -<tr><td class="tal">Breathing-tubes,</td><td class="tar pr1"><div><a href="#Page_109">109</a></div></td><td class="tal pl25 bl">"    primitive,</td><td class="tar pr1"><div><a href="#Page_5">5</a></div></td></tr> -<tr><td class="tal">Bull’s-eye, use of,</td><td class="tar pr1"><div><a href="#Page_32">32</a></div></td><td class="tal pl25 bl">"    simple,</td><td class="tar pr1"><div><a href="#Page_12">12</a>, <a href="#Page_13">13</a></div></td></tr> -<tr><td class="tal"></td><td class="tar pr1"></td><td class="tal pl05 bl">Mildew,</td><td class="tar pr1"><div><a href="#Page_89">89</a></div></td></tr> -<tr><td class="tal">Camera lucida,</td><td class="tar pr1"><div><a href="#Page_25">25</a></div></td><td class="tal pl05 bl">Mirror, concave,</td><td class="tar pr1"><div><a href="#Page_29">29</a></div></td></tr> -<tr><td class="tal">Canada Balsam,</td><td class="tar pr1"><div><a href="#Page_170">170</a></div></td><td class="tal pl05 bl">Mollusca,</td><td class="tar pr1"><div><a href="#Page_161">161</a></div></td></tr> -<tr><td class="tal">Cartilage,</td><td class="tar pr1"><div><a href="#Page_124">124</a></div></td><td class="tal pl05 bl">Mounting,</td><td class="tar pr1"><div><a href="#Page_168">168</a></div></td></tr> -<tr><td class="tal">Cells, animal,</td><td class="tar pr1"><div><a href="#Page_122">122</a></div></td><td class="tal pl25 bl">"   dry,</td><td class="tar pr1"><div><a href="#Page_173">173</a></div></td></tr> -<tr><td class="tal pl1">"  circulation in,</td><td class="tar pr1"><div><a href="#Page_40">40</a></div></td><td class="tal pl25 bl">"   foraminifera,</td><td class="tar pr1"><div><a href="#Page_157">157</a></div></td></tr> -<tr><td class="tal pl1">"  mounting dry in,</td><td class="tar pr1"><div><a href="#Page_173">173</a></div></td><td class="tal pl05 bl">Mosses,</td><td class="tar pr1"><div><a href="#Page_96">96</a></div></td></tr> -<tr><td class="tal pl1">"  pigment,</td><td class="tar pr1"><div><a href="#Page_121">121</a>, <a href="#Page_165">165</a></div></td><td class="tal pl05 bl">Muscle,</td><td class="tar pr1"><div><a href="#Page_127">127</a></div></td></tr> -<tr><td class="tal pl1">"  spiral,</td><td class="tar pr1"><div><a href="#Page_46">46</a></div></td><td class="tal pl05 bl"></td><td class="tar pr1"></td></tr> -<tr><td class="tal pl1">"  vegetable,</td><td class="tar pr1"><div><a href="#Page_37">37</a></div></td><td class="tal pl05 bl">Nails,</td><td class="tar pr1"><div><a href="#Page_124">124</a></div></td></tr> -<tr><td class="tal">Ceramidia,</td><td class="tar pr1"><div><a href="#Page_93">93</a></div></td><td class="tal pl05 bl">Needles,</td><td class="tar pr1"><div><a href="#Page_22">22</a></div></td></tr> -<tr><td class="tal">Chlorophyll,</td><td class="tar pr1"><div><a href="#Page_40">40</a></div></td><td class="tal pl05 bl">Nerve,</td><td class="tar pr1"><div><a href="#Page_127">127</a></div></td></tr> -<tr><td class="tal">Compressorium, Beck’s,</td><td class="tar pr1"><div><a href="#Page_18">18</a></div></td><td class="tal pl05 bl">Net,</td><td class="tar pr1"><div><a href="#Page_133">133</a></div></td></tr> -<tr><td class="tal">Condenser, bull’s-eye,</td><td class="tar pr1"><div><a href="#Page_19">19</a></div></td><td class="tal pl05 bl">Nucleus,</td><td class="tar pr1"><div><a href="#Page_40">40</a></div></td></tr> -<tr><td class="tal pl2">"   substage,</td><td class="tar pr1"><div><a href="#Page_19">19</a></div></td><td class="tal pl05 bl"></td><td class="tar pr1"></td></tr> -<tr><td class="tal">Confervæ,</td><td class="tar pr1"><div><a href="#Page_84">84</a></div></td><td class="tal pl05 bl">Objectives,</td><td class="tar pr1"><div><a href="#Page_16">16</a></div></td></tr> -<tr><td class="tal">Conjugation,</td><td class="tar pr1"><div><a href="#Page_82">82</a>, <a href="#Page_84">84</a></div></td><td class="tal pl05 bl">Objects, drawing of,</td><td class="tar pr1"><div><a href="#Page_24">24</a></div></td></tr> -<tr><td class="tal">Convex lenses,</td><td class="tar pr1"><div><a href="#Page_7">7</a></div></td><td class="tal pl15 bl">"   photography of,</td><td class="tar pr1"><div><a href="#Page_36">36</a></div></td></tr> -<tr><td class="tal pl2">"     foci of,</td><td class="tar pr1"><div><a href="#Page_7">7</a>, <a href="#Page_8">8</a></div></td><td class="tal pl05 bl">Oil-cells,</td><td class="tar pr1"><div><a href="#Page_58">58</a>, <a href="#Page_61">61</a></div></td></tr> -<tr><td class="tal pl2">"     image formed by,</td><td class="tar pr1"><div><a href="#Page_10">10</a></div></td><td class="tal pl05 bl">Oscillatoriæ,</td><td class="tar pr1"><div><a href="#Page_84">84</a></div></td></tr> -<tr><td class="tal pl2">"     virtual image,</td><td class="tar pr1"><div><a href="#Page_11">11</a></div></td><td class="tal pl05 bl">Osmic acid,</td><td class="tar pr1"><div><a href="#Page_170">170</a></div></td></tr> -<tr><td class="tal">Corallines,</td><td class="tar pr1"><div><a href="#Page_164">164</a></div></td><td class="tal pl05 bl"></td><td class="tar pr1"></td></tr> -<tr><td class="tal">Corrosive sublimate,</td><td class="tar pr1"><div><a href="#Page_170">170</a></div></td><td class="tal pl05 bl">Parasites,</td><td class="tar pr1"><div><a href="#Page_153">153</a></div></td></tr> -<tr><td class="tal">Cover-glasses,</td><td class="tar pr1"><div><a href="#Page_18">18</a></div></td><td class="tal pl05 bl">Petals,</td><td class="tar pr1"><div><a href="#Page_69">69</a></div></td></tr> -<tr><td class="tal"></td><td class="tar pr1"></td><td class="tal pl05 bl">Picric acid,</td><td class="tar pr1"><div><a href="#Page_170">170</a></div></td></tr> -<tr><td class="tal">Desmids,</td><td class="tar pr1"><div><a href="#Page_81">81</a></div></td><td class="tal pl05 bl">Pigment,</td><td class="tar pr1"><div><a href="#Page_121">121</a></div></td></tr> -<tr><td class="tal">Diatoms,</td><td class="tar pr1"><div><a href="#Page_85">85</a></div></td><td class="tal pl05 bl">Pocket magnifiers,</td><td class="tar pr1"><div><a href="#Page_13">13</a></div></td></tr> -<tr><td class="tal pl2">"   preparation of,</td><td class="tar pr1"><div><a href="#Page_175">175</a></div></td><td class="tal pl05 bl">Polariscope,</td><td class="tar pr1"><div><a href="#Page_166">166</a></div></td></tr> -<tr><td class="tal">Dipping-tubes,</td><td class="tar pr1"><div><a href="#Page_22">22</a></div></td><td class="tal pl05 bl">Pollen,</td><td class="tar pr1"><div><a href="#Page_71">71</a></div></td></tr> -<tr><td class="tal">Dissection,</td><td class="tar pr1"><div><a href="#Page_20">20</a></div></td><td class="tal pl05 bl">Polyzoa,</td><td class="tar pr1"><div><a href="#Page_147">147</a></div></td></tr> -<tr><td class="tal pl2">"   instruments,</td><td class="tar pr1"><div><a href="#Page_21">21</a></div></td><td class="tal pl05 bl">Pond-hunting,</td><td class="tar pr1"><div><a href="#Page_132">132</a></div></td></tr> -<tr><td class="tal pl2">"   under microscope,</td><td class="tar pr1"><div><a href="#Page_24">24</a></div></td><td class="tal pl05 bl">Preservatives,</td><td class="tar pr1"><div><a href="#Page_169">169</a></div></td></tr> -<tr><td class="tal">Drawing,</td><td class="tar pr1"><div><a href="#Page_25">25</a></div></td><td class="tal pl05 bl"></td><td class="tar pr1"></td></tr> -<tr><td class="tal pl2">"   squares,</td><td class="tar pr1"><div><a href="#Page_26">26</a></div></td><td class="tal pl05 bl">Radiolaria,</td><td class="tar pr1"><div><a href="#Page_157">157</a></div></td></tr> -<tr><td class="tal"></td><td class="tar pr1"></td><td class="tal pl05 bl">Rotifers,</td><td class="tar pr1"><div><a href="#Page_147">147</a></div></td></tr> -<tr><td class="tal">Echinoderms,</td><td class="tar pr1"><div><a href="#Page_162">162</a></div></td><td class="tal pl05 bl"></td><td class="tar pr1"></td></tr> -<tr><td class="tal">Entomostraca,</td><td class="tar pr1"><div><a href="#Page_152">152</a></div></td><td class="tal pl05 bl">Safranin stain,</td><td class="tar pr1"><div><a href="#Page_183">183</a></div></td></tr> -<tr><td class="tal">Epidermis, animal,</td><td class="tar pr1"><div><a href="#Page_122">122</a></div></td><td class="tal pl05 bl">Sap,</td><td class="tar pr1"><div><a href="#Page_128">128</a></div></td></tr> -<tr><td class="tal pl2">"   vegetable,</td><td class="tar pr1"><div><a href="#Page_68">68</a></div></td><td class="tal pl05 bl">Scent-glands,</td><td class="tar pr1"><div><a href="#Page_57">57</a></div></td></tr> -<tr><td class="tal">Extemporised apparatus,</td><td class="tar pr1"><div><a href="#Page_5">5</a></div></td><td class="tal pl05 bl">Sea-weeds,</td><td class="tar pr1"><div><a href="#Page_92">92</a></div></td></tr> -<tr><td class="tal"></td><td class="tar pr1"></td><td class="tal pl05 bl">Section-cutting,</td><td class="tar pr1"><div><a href="#Page_178">178</a></div></td></tr> -<tr><td class="tal">Feathers,</td><td class="tar pr1"><div><a href="#Page_119">119</a></div></td><td class="tal pl05 bl">Seeds,</td><td class="tar pr1"><div><a href="#Page_75">75</a></div></td></tr> -<tr><td class="tal">Fish, scales of,</td><td class="tar pr1"><div><a href="#Page_118">118</a></div></td><td class="tal pl05 bl">Skin,</td><td class="tar pr1"><div><a href="#Page_120">120</a></div></td></tr> -<tr><td class="tal pl1">"  parasites of,</td><td class="tar pr1"><div><a href="#Page_153">153</a></div></td><td class="tal pl05 bl">Spiracles,</td><td class="tar pr1"><div><a href="#Page_102">102</a></div></td></tr> -<tr><td class="tal">Fixation of cell-forms,</td><td class="tar pr1"><div><a href="#Page_171">171</a></div></td><td class="tal pl05 bl">Sponge, fresh-water,</td><td class="tar pr1"><div><a href="#Page_135">135</a></div></td></tr> -<tr><td class="tal">Focus of mirror,</td><td class="tar pr1"><div><a href="#Page_29">29</a></div></td><td class="tal pl15 bl">"   spicules,</td><td class="tar pr1"><div><a href="#Page_155">155</a></div></td></tr> -<tr><td class="tal">Foraminifera,</td><td class="tar pr1"><div><a href="#Page_156">156</a></div></td><td class="tal pl05 bl">Sporangia,</td><td class="tar pr1"><div><a href="#Page_92">92</a></div></td></tr> -<tr><td class="tal">Formalin,</td><td class="tar pr1"><div><a href="#Page_164">164</a></div></td><td class="tal pl05 bl">Stage-forceps,</td><td class="tar pr1"><div><a href="#Page_116">116</a></div></td></tr> -<tr><td class="tal">Frog-plate,</td><td class="tar pr1"><div><a href="#Page_129">129</a></div></td><td class="tal pl05 bl">Starch,</td><td class="tar pr1"><div><a href="#Page_63">63</a></div></td></tr> -<tr><td class="tal"></td><td class="tar pr1"></td><td class="tal pl15 bl">"   mounting,</td><td class="tar pr1"><div><a href="#Page_172">172</a></div></td></tr> -<tr><td class="tal">Gills of mussel,</td><td class="tar pr1"><div><a href="#Page_122">122</a></div></td><td class="tal pl05 bl">Stomata,</td><td class="tar pr1"><div><a href="#Page_49">49</a></div></td></tr> -<tr><td class="tal">Gizzard of insects,</td><td class="tar pr1"><div><a href="#Page_109">109</a></div></td><td class="tal pl05 bl">Suckers,</td><td class="tar pr1"><div><a href="#Page_108">108</a></div></td></tr> -<tr><td class="tal">Glycerine-gelatine,</td><td class="tar pr1"><div><a href="#Page_172">172</a></div></td><td class="tal pl05 bl"></td><td class="tar pr1"></td></tr> -<tr><td class="tal pl2">"   jelly,</td><td class="tar pr1"><div><a href="#Page_171">171</a></div></td><td class="tal pl05 bl">Teeth,</td><td class="tar pr1"><div><a href="#Page_125">125</a></div></td></tr> -<tr><td class="tal"></td><td class="tar pr1"></td><td class="tal pl05 bl">Troughs, glass,</td><td class="tar pr1"><div><a href="#Page_18">18</a></div></td></tr> -<tr><td class="tal">Hairs, animal,</td><td class="tar pr1"><div><a href="#Page_116">116</a></div></td><td class="tal pl05 bl"></td><td class="tar pr1"></td></tr> -<tr><td class="tal pl1">"  vegetable,</td><td class="tar pr1"><div><a href="#Page_53">53</a></div></td><td class="tal pl05 bl">Water-bears,</td><td class="tar pr1"><div><a href="#Page_152">152</a></div></td></tr> -<tr><td class="tal">Heads of Insects,</td><td class="tar pr1"><div><a href="#Page_104">104</a></div></td><td class="tal pl05 bl">Wings,</td><td class="tar pr1"><div><a href="#Page_110">110</a></div></td></tr> -<tr><td class="tal"></td><td class="tar pr1"></td><td class="tal pl05 bl">Wool,</td><td class="tar pr1"><div><a href="#Page_116">116</a></div></td></tr> -<tr><td class="tal">Illumination, correct,</td><td class="tar pr1"><div><a href="#Page_31">31</a>, <a href="#Page_32">32</a></div></td><td class="tal pl05 bl">Worms, fresh-water,</td><td class="tar pr1"><div><a href="#Page_14">14</a></div></td></tr> -<tr><td class="tal pl2">"    dark-field,</td><td class="tar pr1"><div><a href="#Page_34">34</a></div></td><td class="tal pl15 bl">"   marine,</td><td class="tar pr1"><div><a href="#Page_160">160</a></div></td></tr> -<tr><td class="tal pl2">"    for opaque objects, </td><td class="tar pr1"><div><a href="#Page_33">33</a></div></td><td class="tal pl05 bl"></td><td class="tar pr1"></td></tr> -<tr><td class="tal">Imbedding,</td><td class="tar pr1"><div><a href="#Page_180">180</a></div></td><td class="tal pl05 bl">Yeast,</td><td class="tar pr1"><div><a href="#Page_89">89</a></div></td></tr> -<tr><td class="tal pl2">"   by infiltration,</td><td class="tar pr1"><div><a href="#Page_182">182</a></div></td><td class="tal pl05 bl"></td><td class="tar pr1"></td></tr> -<tr><td class="tal">Infusoria,</td><td class="tar pr1"><div><a href="#Page_135">135</a></div></td><td class="tal pl05 bl">Zoœa,</td><td class="tar pr1"><div><a href="#Page_161">161</a></div></td></tr> -<tr><td class="tal">Injection,</td><td class="tar pr1"><div><a href="#Page_164">164</a></div></td><td class="tal pl05 bl">Zoophytes,</td><td class="tar pr1"><div><a href="#Page_157">157</a></div></td></tr> -<tr><td class="tal">Insects,</td><td class="tar pr1"><div><a href="#Page_97">97</a></div></td><td class="tal pl05 bl">Zygnemaceæ,</td><td class="tar pr1"><div><a href="#Page_85">85</a></div></td></tr> -</table></div> - - - - -<hr class="r30" /> - -<p class="tac">PRINTED BY MORRISON AND GIBB LIMITED, EDINBURGH</p> - - - - - - - - -<pre> - - - - - -End of Project Gutenberg's Common Objects of the Microscope, by J. 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