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diff --git a/old/68981-0.txt b/old/68981-0.txt deleted file mode 100644 index 79a16bd..0000000 --- a/old/68981-0.txt +++ /dev/null @@ -1,5969 +0,0 @@ -The Project Gutenberg eBook of Through a pocket lens, by Henry -Scherren - -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 -will have to check the laws of the country where you are located before -using this eBook. - -Title: Through a pocket lens - -Author: Henry Scherren - -Release Date: September 13, 2022 [eBook #68981] - -Language: English - -Produced by: deaurider, Karin Spence and the Online Distributed - Proofreading Team at https://www.pgdp.net (This file was - produced from images generously made available by The - Internet Archive) - -*** START OF THE PROJECT GUTENBERG EBOOK THROUGH A POCKET LENS *** - - - - - - [Illustration: - - PTYCHOPTERA PALUDOSA LIMNOBIA REPLICATA - - _From enlarged photographs, made at the Yorkshire College, - Leeds, from specimens bred by the Author, and mounted by Messrs. - Watson & Son, High Holborn, London_] - - - - - THROUGH - A POCKET LENS - - BY - - HENRY SCHERREN, F.Z.S. - - AUTHOR OF - ‘PONDS AND ROCK POOLS,’ ‘A POPULAR HISTORY OF ANIMALS,’ ETC. - - - _WITH NINETY ILLUSTRATIONS_ - - - THE RELIGIOUS TRACT SOCIETY - - 56 PATERNOSTER ROW AND 65 ST. PAUL’S CHURCHYARD - - 1897 - - - - - Oxford - HORACE HART, PRINTER TO THE UNIVERSITY - - - - - CONTENTS - - - CHAPTER I. - - PAGE - - THE POCKET LENS, THE DISSECTING MICROSCOPE, AND SOME - SIMPLE APPLIANCES 11 - - - CHAPTER II. - - ARTHROPODS AND THEIR CLASSES.--THE MARGINED WATER - BEETLE; THE GREAT WATER BEETLE; THE COCKTAIL - BEETLE 27 - - - CHAPTER III. - - COCKROACHES; EARWIGS; THE GREAT GREEN GRASSHOPPER; - THE WATER SCORPION; THE WATER BOATMAN; CORIXA 63 - - - CHAPTER IV. - - SPIDERS, MITES, AND MYRIAPODS 96 - - - CHAPTER V. - - CRUSTACEANS.--PRAWN, SHRIMP, MYSIS, CRABS; AMPHIPODS; - ISOPODS 128 - - - CHAPTER VI. - - AQUATIC INSECT LARVAE 157 - - INDEX 189 - - - - - LIST OF ILLUSTRATIONS - - - FIG. PAGE - - _Ptychoptera paludosa. Limnobia replicata_ _Frontispiece_ - - 1. Hand Magnifier and Stand 14 - - 2. Zeiss’s Dissecting Microscope 16 - - 3. Leitz’s Dissecting Microscope 17 - - 4. Two Leitz Lenses in holder (open) 18 - - 5. Two Leitz Lenses in holder (closed) 18 - - 6. Home-made Dissecting Microscope 19 - - 7. Beakers 21 - - 8. Glass Capsule 21 - - 9. Glass Block, with cover 22 - - 10. Glass Box, with cover 22 - - 11. Forceps 23 - - 12. Three forms of Dipping-tube. Method of using it 24 - - 13. Mounted Needles 25 - - 14. Cape Peripatus (natural size) 30 - - 15. Margined Water Beetle (male) 32 - - 16. Shells of Molluscs broken up by Dytiscus 33 - - 17. Outline of Dytiscus 38 - - 18. Male Dytiscus in flight 39 - - 19. To show fold of (right) wing of Dytiscus 40 - - 20. To show fold of (right) wing of Dytiscus 40 - - 21 and 21 A. Head of Dytiscus 42 - - 22. Disposition of mouth parts 43 - - 23. Leg of Cockroach 44 - - 24. Tarsus of Dytiscus (magnified) 45 - - 25. Female Dytiscus swimming 46 - - 26. Upper surface of abdomen of typical Beetle 47 - - 27. Spiracle of Dytiscus (magnified) 48 - - 28. Tracheal tubes of Dytiscus (magnified) 48 - - 29. Great Water Beetle 51 - - 30. Female Hydrophilus constructing a cocoon. (After - Lyonnet) 55 - - 31. Cocktail Beetle 58 - - 32. Cockroaches 66 - - 33. Mouth parts of a Cockroach 69 - - 34. Cockroach, showing Spiracles 71 - - 35. Alimentary Canal of Cockroach 73 - - 36. American Cockroach (male) 75 - - 37. Larva and Pupa of Earwig 77 - - 38. Earwig (male) 78 - - 39. Great Green Grasshopper (female) 81 - - 40. Tibial ear of Great Green Grasshopper 85 - - 41. Land Bug (magnified) 86 - - 42. Water Scorpion 87 - - 43. Organs of Water Scorpion, Egg, and Parasitic Mite. - (After Swammerdam) 90 - - 44. Raptorial leg of Water Scorpion 92 - - 45. Water Boatman 93 - - 46. Water Boatman swimming 94 - - 47. Corixa, with wings expanded 95 - - 48. Scheme of under surface of Wolf Spider (female). - Pedipalp of male (enlarged) 98 - - 49. Garden Spider and Web 99 - - 50. Threads of Spider’s Web 100 - - 51. Anchorage of Web 101 - - 52. Foot of Garden Spider 104 - - 53. Spinnerets of Garden Spider 104 - - 54. Jumping Spider 106 - - 55. Falces of Male Jumping Spider 106 - - 56. Foot of Jumping Spider. Scopula much enlarged 108 - - 57. Diving Spiders 109 - - 58. Cell of Diving Spider 112 - - 59. Red Water Mite 114 - - 60. Larva of Water Mite 117 - - 61. Nymph of Water Mite 117 - - 62. Beetle Mite 119 - - 63. _Lithobius forficatus._ Mouth parts seen from below. - (After Graber) 124 - - 64. The Common Millepede 126 - - 65. Segments of Millepede (magnified) 127 - - 66. Prawn 132 - - 67. First walking leg of Shrimp (enlarged) 134 - - 68. Mysis, or the Opossum Shrimp 135 - - 69. Maxillipedes and Maxilla of Shore Crab. (After - Savigny) 138 - - 70. Stomach of Crab laid open 139 - - 71. Gammarus. (After Sars) 142 - - 72. Maxillipedes of _Gammarus marinus_ (magnified) 146 - - 73. Nest-building Amphipod (from life) 148 - - 74. Water Woodlouse 153 - - 75. Mouth-lock. (After Burgess) 161 - - 76. Dytiscus Larvae 162 - - 77. Pupa of Dytiscus 164 - - 78. Larva of _Limnobia replicata_ 167 - - 79. Forked spine of Limnobia (enlarged) 168 - - 80. Pupa case of Limnobia 169 - - 81. Fore wing of Bee, showing marginal fold (×7) 170 - - 82. Larva of _Paraponyx stratiotata_ (enlarged) 173 - - 83. Diagram of segment of Paraponyx, showing arrangement - of tracheal gills 175 - - 84. Gill of Paraponyx larva. (After De Geer) 176 - - 85. Larva of Sialis (enlarged) 179 - - 86. Diagram of Sialis larva, showing arrangement of gills 181 - - 87. Pupa of Sialis 181 - - 88. Larvae of _Ptychoptera paludosa_ (from life) 184 - - 89. Ptychoptera Larva (enlarged). Tail. (After Lyonnet) 186 - - 90. Pupa of Ptychoptera. (After Lyonnet) 187 - - - - - THROUGH A POCKET LENS - - - - - CHAPTER I - - THE POCKET LENS, THE DISSECTING MICROSCOPE, - AND SOME SIMPLE APPLIANCES - - -The object of this little book is to show how much may be seen -with an ordinary pocket lens, and with a simple microscope; and, -as far as possible, to dispel the idea, far too common, especially -among beginners, that no real work can be done unless one has a -compound microscope, with a large battery of lenses and an array of -‘accessories.’ - -It would be easy to multiply quotations, from high authorities, in -support of the proposition implied in the foregoing paragraph. Two only -must suffice. - -In a recent review of a very good book dealing with Butterflies and -Moths (_Natural Science_, vol. vi. p. 293), the following passage -occurs: ‘The only suggestion we should like to make is that a compound -microscope is unnecessary for any of the details that the author -mentions. A first-rate platyscopic hand lens is much more convenient -and the young naturalist should train himself thoroughly in the use -of it. There is no more common error than the undue use of the higher -powers of a microscope. Except for the intimate details of histology, a -low power or a hand lens is much more easy to use, and its employment -gives a much better idea of the structure.’ - -The next quotation is of greater interest, as it gives some insight -into the way in which Darwin carried on his investigations. In the -_Life and Letters of Charles Darwin_ (vol. i. pp. 145, 146) we -are told: ‘His natural tendency was to use simple methods and few -instruments. The use of the compound microscope has much increased -since his youth, and this at the expense of the simple one. It strikes -us nowadays as extraordinary that he should have had no compound -microscope when he went his Beagle voyage; but in this he followed -the advice of Robert Brown, who was an authority in such matters. He -always had a great liking for the simple microscope, and maintained -that nowadays it was too much neglected, and that one ought always to -see as much as possible with the simple before taking to the compound -microscope. In one of his letters he speaks on this point, and remarks -that he always suspects the work of a man who never uses the simple -microscope.’ - -It may be well here to verify the quotations, and also to consult -Darwin’s _Naturalist’s Voyage_, to ascertain what kind of objects -he examined with the simple appliances at his command. In the first -chapter there is an interesting account of a curious limy deposit -on the rocks of the island of St. Paul’s, and of the discoloration -by confervae of the water, which, ‘under a weak lens, seemed as if -covered by chopped bits of hay, with their ends jagged.’ Then we have -an account of the confervae in the Indian Ocean, and of infusoria so -numerous as to tinge the water off the coast of Chile. In the second -chapter we have observations and experiments on planarian worms. -‘Having cut one of them transversely into two nearly equal parts, in -the course of a fortnight both had the shape of perfect animals.’ In -the next chapter he records some observations on the structure of -vitrified tubes formed by lightning striking loose sand. In the fifth -chapter is an elaborate description of a kind of sea-pen; and in the -ninth chapter there are some remarks on the vast number of eggs in the -egg-ribbon of a sea-slug, and on the ‘bird’s-head’ organs in certain -Polyzoa. These remarks were, of course, founded on actual inspection -with the simple microscope. - -To this instrument, also, we owe the discovery of the tadpole-like -larvae of Ascidians, or Tunicates, as they are now generally called. -‘At the Falkland Islands I had the satisfaction of seeing, in April, -1833, and therefore some years before any other naturalist, the -locomotive larvae of a compound ascidian.... The tail was about five -times as long as the oblong head, and terminated in a very fine -filament. It was, as sketched by me under a simple microscope, plainly -divided by transverse opaque partitions, which I presume represent the -great cells figured by Kovalevsky. At an early stage of development the -tail was closely coiled round the head of the larva[1].’ - - * * * * * - -We come now to our pocket lens, which may be purchased for a few -shillings of any optician. One can buy a serviceable single lens, -in an ebonite handle, for a shilling; and this cheap instrument is -sufficiently powerful not only to give the worker a good general idea -of the form and structure of objects, but to enable him to do real -work. With it the habits of many of the inmates of his aquaria may -conveniently be watched; he may see their development from stage to -stage of their life-history; and with it, when they are broken up, he -may make out a good deal of their external and internal anatomy. - - [Illustration: FIG. 1.--Hand Magnifier and Stand.] - -A very good form is shown at Fig. 1, which represents a hand magnifier, -fitted with three lenses of different focus, generally 2 in., 1½ -in., and 1 in. Examination of the catalogues of the principal London -opticians shows that such a set of lenses may be bought for about -3_s._ In shape and construction there is sometimes a little -variation; but the form figured is that most generally adopted, and is, -on the whole, fairly convenient. It would, however, be an advantage if -the hole by which the magnifier is mounted on the stand were drilled -in the solid part of the handle. This would not only do away with the -objection that the hole in the case permits dust to penetrate to the -glasses, when carried in the pocket, but would give a longer reach, and -thus obviate the necessity for moving the stand if the observer were -examining a large object. The price of the stand figured is 2_s._ -6_d._; and one with a short adjusting arm ought not to cost much -more. - -Any one with a mechanical turn may make a stand for himself, though it -may be doubted whether this is quite worth while when these articles -may be bought so cheaply. Nevertheless, there is great pleasure in -making things for oneself; and a home-made stand will enable the -observer to do quite as good work as one that came from the optician’s -shop. - -A bill-file weighted at the foot may be bought for a few pence, and -adapted to the purpose. For the slider a large cork cleanly pierced -will answer admirably. This should carry a piece of stout wire, bent -at the end thus __|[image], to serve as a holder for the magnifier, -which should have a hole in the handle, for the reasons stated above. -The only difficulty will be the attachment of the wire to the cork. The -Rev. J. G. Wood advocated winding the wire round the cork in a spiral; -and this is a very good plan. An increase of steadiness is secured, if -a larger cork, or small bung, be used, and the wire inserted in the -side. - -There are, of course, more expensive lenses, with which better -definition can be obtained. Zeiss has an excellent magnifier consisting -of two lenses, for use in the dissecting microscope (Fig. 2), and -also as a hand lens, at the price of 6_s._; one of the same -construction, for use in the dissecting microscope alone, may be had -for 4_s._ The Steinheil achromatic lenses are probably the best -of all. These are made in powers ranging from 2 in. to ½ in. focus[2]; -and the price varies from 10_s._ up to £1, according to the maker. -Those made by Leitz of Wetzlar cannot be surpassed; and they are sold -in London at 10_s._ each, either mounted in a handle, for use -as hand magnifiers, or with a collar for use in Leitz’s dissecting -microscope (Fig. 3). Mr. Lewis Wright says that ‘the best plan is to -combine both uses, and have two or three powers in collars, with a -spring ring folding into a handle, which will carry any one of them in -that manner. A Steinheil lens at this low price costs little more than -a Coddington, while its performance is infinitely superior[3].’ It is -a difficult thing to get makers to deviate from the beaten track, and -so far as I have been able to learn, Mr. Wright’s wishes have not been -fulfilled. - - [Illustration: FIG. 2.--Zeiss’s Dissecting Microscope.] - -The lenses and stand (Fig. 1) constitute a simple form of dissecting -microscope. If the worker wishes for something more elaborate, he need -only consult the catalogues of the principal makers to find something -that will meet his requirements. Zeiss’s brass stand, with stage, above -which a lens slides up and down in a holder (Fig. 2), is sold for -9_s._; with blocks for supporting the hands, at 10_s._ It is -a useful instrument for small objects. - -My favourite instrument is shown at Fig. 3. Here the focussing of the -lens is effected by rack and pinion work, by means of the screws on -each side the upright pillar. The lens is shown fitted in the collar -which carries it. The stage is of glass--roughly, 2½ in. long by 2 -in. wide, and the arm at the top of the pillar can be moved from side -to side, so as to bring a fairly large object within range. The metal -framework of the stage is furnished with nickelled clips (not shown), -which serve to hold an excavated slip. The arm-rests are detachable, -and the uprights are hinged for convenience of packing. The instrument -(with the exception of these rests) packs into a neat, strong mahogany -box, 7½ in. in length, and about 5 in. in height and width. With -two powers--1 in. and ½ in. are very serviceable ones--the cost is -38_s._ - - [Illustration: FIG. 3.--Leitz’s Dissecting Microscope.] - -It is to be wished that the maker would devise some plan by which the -admirable lenses sold with this instrument could be utilized for the -pocket. Mr. C. Curties, of Baker & Co., High Holborn, has kindly done -something in the matter, and has made for me a metal holder. I have -found this convenient, but should be glad to see something further done -in the same direction, so that instrument, lenses, and holder could be -sold for £2. This ought to be within the range of practical optics. The -spring collar advocated by my friend Mr. Wright seems better, and would -certainly be cheaper. The lenses would only need to be dropped in. To -use my pocket holder one must unscrew the metal collar from the lenses -before screwing them into the metal plates which carry them (Fig. 4). -It is, however, something to have made a beginning: it is a step in the -right direction. - - [Illustration: FIG. 4.--Two Leitz Lenses in holder - (open).] - - [Illustration: FIG. 5.--Two Leitz Lenses in holder - (closed).] - -A serviceable dissecting microscope--not a toy, but an instrument with -which real work may be done--can be made at a cost of a few shillings. -Such a one has been made for me by a friend with a positive genius -for such work. The body is fashioned out of a parcel-post box 7 in. -long, 3½ in. in height, and the same in width. From the centre of the -sliding top a piece is cut away, leaving ledges to take a 3 in. by 1 -in. excavated slip for small dissections, or a mounted slide of a large -object, such as a whole insect, for examination. A further portion is -cut away on each side to take a small dissecting dish (Fig. 6). To -admit the light, a hole is cut in the side of the box; and the mirror -consists of a piece of silvered glass which was bought of a hawker in -the street. This is placed in the box opposite the square hole, and -sloped at an angle of 45°. The aid of a skilled mechanic was sought -for a small rod carrying a thread, which works in a piece of brass -bent at a right angle. This piece of brass is screwed on the box, just -above the aperture by which light is admitted, and carries a pocket -magnifier, similar to that shown at Fig. 1. - - [Illustration: FIG. 6.--Home-made Dissecting Microscope.] - -This modest little instrument generally stands on my work-table, and -has provoked some remark and a little good-natured banter from friends -who have seen it. Nevertheless, I should be sorry to part with it, for -I have found it extremely serviceable in many ways. And more than one -critic has had to confess that better results were obtained than one -would expect from its appearance. The total cost out of pocket was, -3_d._ for the box, 3_s._ for the lens, and 1_d._ for the plate-glass, -while the man who made the pillar and ear-piece would take no more -than 6_d._ for his work. This brings the total to 3_s._ 10_d._ With a -little ingenuity the pillar might be made to carry a collar, and so -take a Steinheil lens. This would swell the total cost to about 11_s._ - -Other apparatus need not be costly. An incident occurred at the meeting -of the Quekett Microscopical Club on November 22, 1878, which shows -how readily common objects may be utilized for our purpose. The late -Right Hon. T. H. Huxley, who was at that time President, exhibited, -and made some remarks on, the dissecting microscope which now bears -his name. During the discussion which followed, Professor Charles -Stewart exhibited some little saucers, which were admirably adapted -for dissecting purposes. The President said that he should ‘be glad -to know where these convenient little saucers could be obtained.’ The -next paragraph of the minutes is interesting and instructive. ‘Mr. -Stewart said they were to be found at the corners of the streets, -containing three whelks or three mussels for a penny. He bought those -he had brought to the meeting at a shop in the New Cut, where they were -supplied to costermongers[4].’ - -As very many of the objects with which we are concerned are aquatic, -we shall want vessels of some sort to serve as aquaria. Any glass -vessel will answer our purpose, provided it is clear, to allow of the -examination of our captives; or shallow pie-dishes may be utilized. -The glass pots in which preserves are sold will do admirably, and any -glazier will cut us covers for a few pence. Within reasonable limits, -the smaller the aquaria are the better. The inmates can be seen more -easily, and picked out with less trouble when one wishes to examine -them. - -The principles on which aquaria should be kept are now pretty generally -understood. There should always be a small quantity of growing aquatic -vegetation, and a supply of minute life to furnish food for the larger -forms. Excess of light should be avoided, and the temperature should -not be allowed to rise much above 50° F. Carnivorous beetles and their -larvae may be fed with small pieces of meat, small garden worms, or -tadpoles. Most of the smaller larvae treated of will be satisfied with -vegetarian diet, varied with an occasional meal of water-fleas. - - [Illustration: FIG. 7.--Beakers.] - - [Illustration: FIG. 8.--Glass Capsule.] - -If one cannot lay the household stores under contribution for jam-pots, -tumblers, and bottles, beakers (Fig. 7) make capital small aquaria. -They are sold in nests, and may be had either rimmed or lipped--rimmed -for choice. There is no difficulty in obtaining them of any optician or -glass-merchant. Mine have been bought from Messrs. Beck, of Cornhill, -as have the capsules, &c., figured here. - -Glass capsules (Fig. 8) are made in different sizes, ranging from 1½ -in. to 3 in. in diameter, with a height of 1 in. or 2 in. The largest -size, 3 in. by 2 in., costs 5_d._, and a glass circle to cover it, -1_d._ These capsules will be found useful for small aquaria, and -for isolating aquatic larvae in order to keep them under observation -during their change to perfect insects. It was in a capsule of this -kind that some of my Ptychoptera larvae (p. 184) were kept, and changed -into the pupal condition. - -The glass block, with cover (Fig. 9), is convenient for a number of -purposes. In it small creatures may be examined in air or in water, and -it makes an exceedingly convenient little dissecting dish for use with -the mounted hand magnifier (Fig. 1), or with Leitz’s stand (Fig. 3), or -the home-made stand (Fig. 6). The glass box, with cover (Fig. 10), is -extremely good for keeping small creatures under observation. - - [Illustration: FIG. 9.--Glass Block, with cover.] - - [Illustration: FIG. 10.--Glass Box, with cover.] - -Excavated glass slips, 3 in. by 1 in., may be bought from any optician. -They serve for the examination of objects in water, and also for -dissection. The best I have been able to get have been supplied by Mr. -J. Hornell, of the Biological Laboratory, Jersey, and they are very -cheap. - -We shall need some forceps to pick up specimens from the vessels -in which they are kept, and the same little instruments will be -found convenient in collecting. Both forms have advantages of their -own; if we are limited to one pair, they should be curved, and of -brass. Forceps with ivory tips are very useful for handling aquatic -vegetation. These articles are not usually sold by opticians, but -are kept by the tradesmen in Clerkenwell who sell jewellers’ and -watchmakers’ tools, and cost from 1_s._ to 1_s._ 6_d._ a -pair. - - [Illustration: FIG. 11.--Forceps.] - -Dipping-tubes are used to take up small aquatic animals from the -vessels in which they are kept. Very little practice will render the -use of this instrument easy. The tube is held firmly between the thumb -and the third and fourth fingers of either hand, while the index finger -is pressed firmly on the top. Most people naturally prefer the right -hand, but it is well to accustom oneself to use the right or left -indifferently. The open end is then put into the water, just over the -object to be secured, and the index finger lifted. The rush of water -into the tube will carry the object into it, and if the finger be again -applied to the top, the pressure of the atmosphere will prevent the -water from escaping when the tube is lifted out[5]. - -Small brushes are useful for taking up specimens from the water or from -pickle; common ones will do very well for large objects, but for small -objects and parts it is advisable to have one or two sable brushes, as -these form a better point. - -Some needles fixed in handles will also be necessary. These may be -bought, or made by fixing ordinary needles of requisite sizes into the -handles sold for small brushes. The needles must be kept free from -rust, and should always be carefully wiped after use. A good plan to -keep them clean is to stick them in a gallipot in which has been -melted a mixture of lard and paraffin in equal proportions. - -Small dissecting-knives are useful, but all the work described here may -be done with an ordinary pocket-knife in good trim. - - [Illustration: FIG. 12.--Three forms of Dipping-tube. - Method of using it.] - -The best preservative for our purpose is formalin, which is sold in -a forty per cent. solution. This should be treated as absolute, and -a five per cent. solution made. This will really be a two per cent. -solution, and is sufficiently strong for general use. - -The most profitable use we can make of specimens is to watch their -habits while living, and to break them up and learn as much as we can -about their structure when they are dead. For us to make a collection -of specimens in tubes would be a waste of material. - - [Illustration: FIG. 13.--Mounted Needles.] - -Little need be said about collecting. The objects treated of are -so plentiful that no great skill, nor any wealth of appliances, is -needed to secure an ample supply. The following remarks on the methods -employed at the Illinois State Laboratory for the capture of aquatic -insects and larvae are, however, worth quoting:-- - -‘Insects in vegetation, and on or in the bottom, were taken by means of -a dip-net--a net of about equal depth and width attached to a strong -semicircular ring, firmly fixed to a long handle, the straight side of -the ring being opposite the point of attachment. For the larger and -more active forms, a coarser net was used, and for smaller forms one -made of finer net proved most durable and satisfactory. To collect from -the mud of the bottom, the water immediately over it was violently -stirred and then swept with the net. The surface layer of mud was also -scooped up in the fine dip-net, and then allowed to wash through, -leaving the coarser contents in the net. Insects on the bottom in deep -water were secured by using a dredge, and washing its contents through -net sieves. The aquatic vegetation, when free from mud, was violently -washed in a large pan, many smaller forms being thus dislodged and -coming to the surface. Insects occurring in open water were taken in -drawing an ordinary towing-net[6].’ - -Here we have, so to speak, the general principles of collecting. It -will be easy to adapt them to particular cases. - -In choosing the subjects to be treated of in this little book, some -difficulty has been experienced in deciding what to select from the -multitude that lay ready to hand. It was felt necessary that the -subjects should be connected, since choosing them at random would -lead to purposeless work, and so to waste of time and opportunity. -After some consideration, the author has decided to take all the -examples from the Arthrop´oda--that great sub-kingdom of backboneless -animals which includes the Lobster, the Crab, the Sand-hopper and the -Woodlouse, the Spider and the Mite, the whole world of Insects and the -Centipedes. One cogent reason that influenced this decision was the -fact that these objects are exceedingly common, so that there can be no -difficulty in procuring material on which to work. There is, perhaps, -no other sub-kingdom so full of interest, on account of the many widely -different forms, which may be referred to one common plan. - -It may possibly appear to some readers that the powers of the pocket -lens have been exaggerated. As a matter of fact the material for the -book has been gathered by actual observation. The author has seen, with -an ordinary pocket lens, the objects here described. If some are shown -as they would appear under greater magnification than such a lens would -give, this is chiefly for the sake of emphasizing points of interest -which might otherwise be overlooked, but which can readily be made out -with a hand magnifier, when attention has been drawn to them, and the -observer knows what to look for. - - - - - CHAPTER II - - ARTHROPODS AND THEIR CLASSES.--THE MARGINED - WATER BEETLE; THE GREAT WATER BEETLE; - THE COCKTAIL BEETLE - - -Having got together our apparatus, which, as we have seen, need be -neither costly nor complicated, the next step will be to acquire some -knowledge of the group from which the examples here treated of will be -taken--the Ar´thropods, or animals with hollow-jointed limbs. These -are the ‘Insects’ of the Linnaean classification, and, for the matter -of that, of popular phraseology; for though few people would now -venture to call a Lobster an ‘insect,’ we still style some of its near -relatives Water ‘Fleas,’ as Swammerdam did two hundred years ago. - -The Arthropods form a phylum, or main division of the Animal Kingdom. -Above this phylum comes that of the Molluscs, or soft-bodied animals, -such as the Oyster, the Snail, and the Cuttlefish. Still higher are the -Lancelet, the Sea-squirts, and some few others, that bridge the chasm -between the phyla without, and that phylum with, a backbone. And to -this last Man himself belongs. - -Two reasons contributed to the selection of the Arthropods as a subject -for work with the pocket lens: (1) the great interest which surrounds -many of the group; and (2) the ease with which specimens may be -procured and kept under observation. - -Every one has pretty clear notions as to the general ‘make’ of a -Vertebrate or backboned animal. An Invertebrate animal has, of course, -no backbone or the semblance of one; the nervecord, where present, lies -on the under surface, and forms a ring round the gullet, and the heart -lies on the upper surface or back. We may verify this by pulling to -pieces a dead insect. - -But a phylum, or main division, is much too large to be considered as a -whole. It must, therefore, be broken up into smaller groups, which are -called Classes, generally reckoned as five in number. These, again, may -be grouped into two divisions, according as their members breathe by -means of air-tubes (_tracheae_) or by gills. Our scheme then will -stand thus:-- - - { { Peripatus. - { Breathing by { Centipedes and Millipedes. - { air-tubes { Insects. - ARTHROPODS { { Spiders and their kin. - { - { Breathing by { Lobsters, Crabs, Sand-hoppers, - { gills { and Woodlice. - -This scheme looks well on paper; and on the whole is workable. But -among our examples chosen from the Class of Insects, we shall find some -that breathe by gills in their larval stage, and by air-tubes when -adult. And among the Crabs are some, the gills of which have ceased -to perform their normal function, so that these animals cannot live -in water for a single day. And then there are the Sand-hoppers and -Woodlice. - -The body of an Arthropod may be represented by a series of similar -rings, thus: - - [Illustration] - -This similarity is clearly apparent in the Centipede, but is concealed -in the Beetle, the Shrimp, and the Spider. It seems, at first sight, -to be altogether lost in the Crab, and does really vanish in the adult -stage of some parasitic Crustaceans. - -It may be plausibly objected that our ideal Arthropod resembles nothing -so much as a worm. In many respects this is true. A primitive Arthropod -was worm-like, as is a Centipede. And Arthropods and Worms were -formerly classed together in one group, as Annulo´sa or ringed animals. -The chief external difference lies in the nature of the appendages -borne by the various rings or segments. - -We may represent those of the Worms thus [image], for they are -bristles, or groups, or modifications of bristles. Those of the -Arthropods may be represented thus [image], for the appendages are -really jointed, though, of course, in a fashion different from those of -a backboned animal. - -The jointed appendages of Arthropods may be modified to fulfil very -different functions. They may serve as legs for walking, hands for -climbing or seizing prey, jaws for masticating food, feelers or organs -of touch and sense, and, strange as it may seem, in one group, as eyes. - -It is well to get some notion of how these joints are formed. To take -the body first: the skin connecting the segments is much thinner than -that of the segments themselves, which is thickened by the deposition -of chitine, and, in some cases, also of carbonate and phosphate of -lime. A portion of the body, then, may be represented thus, [image] -where the heavy lines denote the segments, and the thin ones the spaces -between the segments. It will be seen that this arrangement allows -of considerable play, and also of a telescopic movement by which the -segments can be brought close together. - -It is easy to construct a kind of model that shall exemplify these -movements. Make a tube of calico, some six inches long, and having -stuffed it with cotton-wool, paste on it strips of brown paper one inch -in width, leaving an interval between each, as in the last diagram. -Then we shall be able to understand how Arthropods can bend the body or -move it from side to side. And the limb joints are made on a similar -plan. - - [Illustration: FIG. 14.--Cape Peripatus (natural size).] - -The most archaic Arthropod--Perip´atus--must be mentioned. It is not -found in Britain, nor even in Europe; so that, unless we travel, we -shall only know it from books, or from museum specimens. But it is an -extremely interesting creature, for it is of worm-like aspect, and -breathes by air-tubes, opening all over the body, which has no external -segments. The limbs are imperfectly jointed, and each of them bears -two claws. Most naturalists make this genus a Class by itself, while -some put it with the Centipedes. There are about a dozen species, four -of which are African, two Australian, and the rest are found in South -America and the West Indies. Besides these there are some doubtful -species. - -In habit they resemble the Centipedes, and they ensnare the insects on -which they feed by ejecting sticky slime from the small processes near -the mouth. The left process is shown in the illustration, just below -the antenna of that side. - -Professor Sedgwick, who described these animals in the _Quarterly -Journal of Microscopical Science_ (1888), and, more popularly, -in the _Cambridge Natural History_, says, that ‘the exquisite -sensitiveness and changing form of the antennae, the well-rounded plump -body, the eyes set like small diamonds on the side of the head, the -delicate feet, and, above all, the rich colouring and velvety texture -of the skin, all combine to give these animals an aspect of quite -exceptional beauty.’ - -Unfortunately, an illustration in black-and-white can only render -form. We must take the beauty of the colouring for granted. One thing, -however, cannot escape the most cursory examination of the picture--the -resemblance of the creature, in some respects, to a worm, and, in -others, to a caterpillar, which, as everybody knows, is the larval -stage of a butterfly. If this resemblance sets us thinking how it came -about, and what it means, Peripatus will, for the present, have done -its work for us. - - * * * * * - -With these general notions of Arthropods, we may pass on to put our -pocket lens to some practical use. Our first subject shall be the -Margined Water Beetle (_Dytis´cus margina´lis_), which can be -taken in almost any open pond in the country. Water covered with -duckweed should be avoided in hunting for these beetles, which prefer -ponds with a clear surface, so that they may easily come to the top to -breathe. - -Every one has a good general notion of the principal Insect-groups, -technically called Orders--Beetles, Cockroaches and Grasshoppers, -Butterflies, Bees and Wasps, and Flies. Insects may be defined -as animals with hollow-jointed limbs, and divided into three -regions--head, thorax, and abdomen. The head bears a pair of antennae; -the thorax carries three pairs of legs, and (generally) two pairs of -wings; the abdomen is without appendages. Insects when adult breathe -by tubes that open to admit air. In Chapter VI we shall see that many -larvae obtain an air supply in different ways. - - [Illustration: FIG. 15.--Margined Water Beetle (male).] - -Beetles may be taken as very good types of true Insects. They -constitute the Order Coleop´tera, or Insects with sheathed wings, only -the hinder pair being used for flight (Fig. 18), and at other times -they are folded under the wing-cases, or el´ytra, as in Fig. 15. - -We may advantageously compare our Beetle with Peripatus, and note the -points of agreement and of difference. - -Now, if our captive Beetles are to yield us the greatest possible -amount of profit, we shall keep them under observation for some time, -so as to watch their habits. - -In keeping these Beetles we shall not require a large aquarium. A small -gathering of aquatic weed will be necessary to keep the water in good -condition and the aquarium ready for its tenants. - -My interest in these Beetles was quickened by a letter in the -_Field_ (Oct. 28, 1893), in which a correspondent at Weybridge -asked ‘for information as to what animal or bird bisects so neatly the -shells of the Water Snail (_Planorbis_).’ I thought then, and -know now, that the shells were ‘bisected,’ if that is the proper word, -by Water Beetles. From that time I have had, and still have, several -living in small aquaria, but for a long time was unable to get direct -evidence on the subject. - - [Illustration: FIG. 16.--Shells of Molluscs broken up by - Dytiscus. - - (From a photograph by Cherry Kearton.)] - -Many experiments were tried, and at last these proved successful. -Several specimens of Dytiscus[7] were obtained, and put into a small -aquarium in which was no other food for them than some snails and other -molluscs. The Beetles were carefully watched, and were several times -seen trying the snails. In crawling along the inner surface of the -glass, Planorbis and Limnaea both protrude the foot to a considerable -extent, and pieces were ripped out by the strong mandibles of the -Beetles before the shells were actually broken up. - -All the shells represented in Fig. 16 were taken from this aquarium, -so that there is good evidence as to what creatures broke them up and -devoured their inmates. In these, as in the specimen kindly sent me by -Mr. Tegetmeier, the Natural History Editor of the _Field_, the -bisection is not complete, though in all cases it is carried far enough -to allow of the extraction of the mollusc. The large Limnaea shell in -the centre has been attacked, but it seems to have been left when the -beetles discovered it was empty. (The empty shell was noted before the -Beetles were put into the tank.) Another Limnaea shell is figured, from -which the snail has been picked out, and that of a fresh-water mollusc. - -After these observations had been recorded in the _Field_[8], I -found that I had been anticipated by about forty years. I picked up, -at a bookstall, a copy of G. B. Sowerby’s _Popular History of the -Aquarium_, and there I found that the author had distinctly seen -Dytiscus at this kind of work. He says[9]: ‘I have only once witnessed -him in the act of seizing an unfortunate Planorbis or Flat-coiled Water -Snail. At first, the Dytiscus seemed to be roaming about in quest -of something, first under, then over, the leaves of a water-lily. -At last, in a rather dark corner, he seemed to perceive suddenly a -Planorbis which was browsing upon the stem of a plant just under the -shade of a broad leaf. He darted at this, seized it, and then, putting -his tail out of water, for the purpose of taking in a fresh supply of -air, moved slowly down, bearing the snail with him. He held it by his -fore-feet, turning round the coil until the aperture of the shell was -opposite his mandibles, then he began nibbling away at the animal. In -vain did the poor mollusc try to withdraw within its shelly fortress, -for the beetle picked off the edges of the shell bit by bit, so as to -expose the body as fast as it was withdrawn. All the way down to the -bottom of the tank was this process continued, air-bubbles rising to -the top, and bits of broken shell falling, till the beetle with his -burden reached a stone near the bottom, where I left him still busy at -his work.’ - -This puts the matter beyond doubt, if any before existed. I at once -wrote to Mr. Tegetmeier to let him know that my experiments had, -unknown to me, been anticipated, long ago, by Mr. Sowerby. Had -he rescued his Planorbis shell, it would have compared very well -with those forwarded to the _Field_ office in 1893. They had -been exhibited at the Malacological Society, and no one was able -to solve the mystery of their mutilation. This shows, to quote the -_Field_[10] on the subject, ‘how easily statements that have been -recorded may subsequently be overlooked and entirely forgotten.’ - -To return to our Beetle. The male is a handsome creature, from an inch -to an inch and a quarter long, clad in olive-green, bordered with -yellow, and exceedingly active. His mate is smaller, more soberly clad -in brown, without the yellow markings, and the wing-cases are more or -less furrowed. - -The first thing to notice is the shape of the body, oval and smooth, -offering no resistance to the water. The hind pair of legs are -flattened and fringed with hairs, so as to make capital paddles. In -swimming the right and left legs are moved together. - -Now, though this Beetle lives in the water, it is made, so far as -concerns its breathing apparatus, after the fashion of a Land Beetle, -and consequently is compelled to come to the surface pretty frequently -for a supply of air, which it obtains in this wise. Directly it ceases -paddling it floats to the top of the water; and as the head is heavier -than the tail the latter projects a little above the surface. Then the -wing-cases are raised, and air flows in under them to the breathing -holes on each side. The operation is not a long one, and as soon as it -is over the Beetle is ready for another ramble round his dwelling-house. - -But if we do not supply our captive with food that he may take for -himself, it is only right that we should feed him, which may be done at -intervals--say, every other day. ‘Little, and often,’ is an excellent -motto to guide us in our feeding; and though its adoption may entail -some trouble, it will be more than compensated by the success that -will attend our endeavours to keep the inmates of our aquarium in good -condition. And the operation of feeding our Beetle will show us that he -has some capital sense-organs, which are of as much, if not of more, -use to him than his eyes. - -He is a flesh-eater. Let us take a small piece of meat or fish in a -pair of forceps, or stuck on a pointed stick, and hold it at a little -distance from his great eyes. The chances are that he will not see it. -Even if we put it in front of him, he is quite likely to disregard it, -for he has nothing corresponding to a nose, with which he may smell. -From his head there spring a pair of long feelers--the antennae--and by -means of these we will let him know that his dinner is ready. That is -effected by drawing the food along the side of one of the antennae. The -creature undergoes a sudden change. Till the antenna was touched with -the food he was resting on his swimming legs. But in a moment down goes -his tail and up goes his head, he stretches out his raptorial legs, and -clutches wildly at the forceps or stick, as the case may be, holding so -tight that he may be dragged round and round the glass vessel. Let go -he will not, of his own accord; and it would be a difficult matter to -shake him off. Similar experiments may be tried with other Beetles, and -the result will be to impress on the mind the fact that the feelers are -capital sense-organs. - -If we are to turn our Beetle to the best account, we shall need to -handle him. It may be inconvenient to wait till he dies, so we will -kill him quickly and painlessly by plunging him into boiling water, and -he may be preserved by putting him into a tube containing about equal -parts of water and spirit, or a five per cent. solution of formalin. - -Dissections should properly be made under water. The Beetle should be -fastened, back upwards, to a piece of cork weighted with lead, and -placed in a deep saucer, or dissecting dish, and covered with water. -But a good deal of rough dissection, as is ours, may be done in air, -and the Beetle may be fastened to any convenient piece of board, or -even held in the palm of the left hand. Very little practice is needed -to run over the external parts of a large Beetle in this manner. - - [Illustration: - - FIG. 17.--Outline of Dytiscus (male). _a_, - antenna; _b_, maxillary palp; _c_, eye; _d_, - fore-leg; _e_, thorax; _f_, middle leg; _g_, - elytron; _h_, suture; _i_, hind leg; _j_, claw; - _k_, tarsus or foot; _l_, tibia or shank; _m_, - femur or thigh; _n_, first three joints of foot, widened - into a plate with suckers beneath.] - -First, let us look over our Beetle, and get some general notions of -its make. As it lies, back upwards, it is clear that it consists of -three parts or regions------------[image], the first of which is the -head, the second the thorax, and the third the abdomen. Not only in our -Beetle, but in Insects generally, these parts correspond to the words -that denote them, in that the thorax is longer than the head, and the -abdomen longer than the thorax, as shown by the three dashes, a few -lines above. - -These divisions are well shown in Fig. 17, where other parts are also -marked. It will pay to go over our own specimen with this figure before -us, and so make acquaintance with the several parts, to some of which -we shall return in greater detail. - - [Illustration: FIG. 18.--Male Dytiscus in flight.] - -At this point, if we have not done so before, it will be convenient -to fasten our Beetle, in the position figured, by a stout pin driven -between the thorax and the abdomen, just above the suture (_h_). -We want to raise one of the wing-cases. - -If a needle be taken in each hand, between the thumb and first two -fingers, and that in the left hand be used to steady the creature, the -wing-case on the right may be raised with the needle in the right hand, -and then cut off. The small filmy membrane, of somewhat triangular -shape, which comes off with the wing-case, is the winglet. There is -one on each side; and their vibration causes the humming noise made by -these insects in flight. When the water dries up in one pond, or food -becomes scarce, they will leave and fly off to another. - -The wing lies folded upon the abdomen. A good deal of very interesting -matter has been written on the way in which Insects fold their wings, -but we can see for ourselves how this Beetle folds them. All we have to -do is to take the wing, and draw it gently away from us, and so unfold -it. We may use finger and thumb, or a small pair of forceps. When let -go, it will spring back to its old position. Reference to the expanded -wing in Fig. 18, and to the diagrams Figs. 19 and 20, will show how the -wing is folded. - - [Illustration: FIG. 19.--To show fold of (right) wing of - Dytiscus.] - - [Illustration: FIG. 20.--To show fold of (right) wing of - Dytiscus.] - -The cross-mark in the diagram represents a joint in the chitinous rod -that forms the wings. This lies just above the cell (which is left -white in Fig. 18). The shorter part of the rod is bent down, forming an -acute angle (Fig. 20); of course, carrying with it the membranous part -of the wing. - -This may seem a little difficult. But if it be tried on a specimen, no -real difficulty will be experienced. When the wing has been unfolded, -it will, if let go, spring back to its old position, the shorter part -lying underneath, and the chitinous rod fitting into a groove formed by -the projecting sides of the segments of the abdomen. - -To this point the sum of our knowledge about Dytiscus amounts -to this: It is aquatic in habits; its body is divided into three -regions; and it has a pair of membranous wings, covered by chitinous -wing-cases, or sheaths, technically called _el´ytra_ (each being -an _el´ytron_). Wing-cases of this kind are the distinguishing -mark of the Beetles, or _Coleop´tera_, though they are not always -so well developed as in the specimen with which we are dealing. This we -can discover for ourselves by examining all the Land Beetles met with -in a country ramble or in a stroll round the garden. - -Now let us unpin our Beetle, turn it on its back, and examine it from -the under side. Head, thorax, and abdomen may be made out more clearly -than before, and we can see that the last two regions are divided into -segments. - -Let us deal with the head first. This may be easily separated from the -thorax with a dissecting needle, or with a pocket-knife--an exceedingly -handy tool. The huge goggle-eyes cannot escape observation; and, even -without a magnifier, they may be seen to be compound--that is, made up -of a number of facets, which show like a fine network. - -Just in front of the eyes are the antennae, which serve as organs of -touch and perhaps also of other senses. - -Kirby has recorded facts which seem to show that the antennae (in -some cases) are also organs of hearing. Other authorities, after many -observations, have come to the same conclusion. The matter, however, -is beset with difficulty. It is certain that some Insects have their -ears in their legs; and for the present, at any rate, we may be -satisfied to know that the antennae are sense-organs, certainly of -touch, probably of smell, and, in some cases, of hearing. An excellent -authority on the subject is Sir John Lubbock’s book, _The Senses of -Animals_[11], which contains references to very many original papers. - - [Illustration: FIG. 21. - - FIG. 21.--Upper surface of head of Dytiscus. _a_, - labrum, or upper lip; _b_, clypeus or shield; _c_, - mandible dissected out, and (_d_) reversed; _e_, eye; - _f_, antennae.] - - [Illustration: FIG. 21 A. - - FIG. 21 A.--Under surface. _a_, mentum or chin; _b_, ligula - or tongue; _c_, labial palp; these three together forming - the labium, or lower lip; _e_, eye; _f_, antennae. Above the - maxillae, or lower jaws (_d_ _d_), are shown dissected out: - _d^1_, inner or palpiform lobe; _d^2_, maxillary palp; _d^3_, - lacinia or blade; _d^4_, the palpifer or piece that bears the - palp (_d^2_); _d^5_, stipes or stalk; _d^6_, the cardo or hinge.] - -Now we may pass to the mouth parts. It will be good practice to dissect -these out, either in air or in water. We may hold a Beetle between the -finger and thumb of the left hand, and separate all the parts with a -needle held in the right. It is a good plan to gum these parts on a -card, for comparison with the figures in our favourite book--whatever -that may be--on Natural History, and also with the mouth parts of -insects of other Orders. For however much these may differ in form, -and in the uses to which they are put, they are really modifications -of the same parts. - -In Fig. 21 we have the upper side and in Fig. 21A the under -side of the head represented, so that we may easily get acquainted -with the different parts, and the names given to them. The cut should -be gone over several times, and the parts in the picture compared with -those in the specimen under consideration. It is good practice to -endeavour to draw what is seen from the specimen itself, and then to -compare the result with the work of the trained artist. And the mouth -parts of Dytiscus may be compared with the mouth parts of the Cockroach -(Fig. 33). - - [Illustration: FIG. 22.--Disposition of mouth parts.] - -Returning to practical work, the first thing is to separate -the _labrum_, or upper lip, from the head. Then the large -_mandibles_ should be dissected out, and cleaned (by soaking in -caustic potash) from the muscles which will come away with them. Behind -these are a smaller pair of jaws, the _maxillae_, furnished with -a pair of palps, called maxillary palps from their position. These are -to be dissected out; and then the lower lip, or _labium_, may be -separated by passing a sharpened needle along the line where it joins -the chin. The palps on the lower lip are called labial palps. - -When these parts are cleaned and dried, they should be gummed on card, -as shown in Fig. 22, where the long lines represent the upper and lower -lips respectively, and the shorter ones the mandible and maxilla of -each side. - -So much for the head. Now we discover that what appeared to be the -thorax, when we were looking at the upper surface of the Beetle, and -what is called the thorax in descriptions of Beetles, is really but -a portion of that region, which is seen to be divided into segments. -The covering on the upper surface protects only the first segment, -the middle and hinder ones being covered by the wing-cases and the -_scutellum_ (a triangular piece jutting backward from the second -segment, and meeting the suture). This is not represented in Fig. 17; -but we may put in with our pen a tiny triangle, with its base towards -the head, and its apex towards the tail--this will meet the case. - -The first segment bears no appendage above, but to the under side is -attached the first pair of legs. The middle segment also carries a pair -of legs, and on its upper surface are the wing-cases, to the under side -of which, and to the body, the winglets are joined. The last segment -bears the wings above, and the last pair of legs below, these being -placed very far back, so as to give them greater power in propelling -the animal through the water. - -It will be convenient to examine the legs next. First, however, it -will be well to look at a normal leg of an Insect (the Cockroach), and -learn the names of the different parts. First comes the _coxa_ (_a_) or -haunch, next the _trochanter_ (_b_), then the _femur_ (_c_) or thigh, -the _tibia_ (_d_) or shank, and the _tarsus_ (_e_) or foot, ending in -a pair of claws. There are three pairs of legs in perfect Insects, and -usually the same number in larval forms, though in some of these legs -are entirely wanting. - - [Illustration: FIG. 23.--Leg of Cockroach.] - -In the males of the Margined Water Beetle and many of its near -relations the first pair of legs deserve special attention. The first -three joints of the tarsus have coalesced to form a disk or cup, which -in our specimen bears two smaller ones on its inner surface. A power -of 20 will show the disk nearly as well as it appears in Fig. 24. -The purpose of this disk, or clasper, which is absent in females, is -obvious. It was formerly supposed to act as a sucker, but Professor -Lowne and Professor Miall[12] have shown that it does not act by -atmospheric pressure, but by a viscid secretion discharged from the -cup-like hairs with which the inner surface is set. - - [Illustration: FIG. 24.--Tarsus of Dytiscus (magnified).] - -The middle pair of legs in the male also bear cup-like hairs on the -corresponding joints of the tarsus, and in very much greater number. -Professor Miall quotes Simmermacher to the effect that while the large -disk on the fore-leg has 170 sucking-hairs, the enlarged joints of -the tarsus of the middle leg bear no less than 1590. These hairs are -plainly discernible with the half-inch Steinheil, and I have made them -out with the inch, and think that I could show them to anybody else -with that power. I have not looked for these sucking-hairs on the -middle leg of other Beetles of the same family which have disks on -their fore-legs, but they do exist in some other genera. - -If we watch a male Dytiscus in life, in a small aquarium, we shall soon -be convinced that Lowne and Miall are correct in their statement that -the cup-hairs discharge an adhesive substance. We shall see this all -the more plainly if there is much floating vegetation. For, in swimming -about, the Beetle will often come in contact with some of this, and it -will adhere to the cup-hairs. His struggles to free himself from the -encumbrance will show that the attachment is not altogether under his -control. The offending weed is rubbed against the spines of one of the -other legs till it is removed. - - [Illustration: FIG. 25.--Female Dytiscus swimming.] - -The spines with which the legs are set are worthy of a good deal of -attention, and, like the adhesive cup-like hairs, though in different -fashion, they doubtless assist the animal in holding its prey. The -first and middle legs end in strong claws; those of the last pair are -not so well developed. - -The last pair of legs are the swimming organs. The tibia and tarsus -are fringed with long stiff hair behind, so as to hold the water -when the Beetle swims. A peculiar arrangement of the first joint of -the tarsus allows the edge to be presented to the water when the limb -is carried forward for the return stroke, thus offering the least -possible resistance. This Dr. Sharp has compared to the action of a -rower in feathering his oar. There is, however, this difference, which -it is well to note. The oar is feathered after the stroke; the Beetle -feathers its legs before the stroke. It is the first motion when it -begins to swim, and the action is not peculiar to the male. - -We now come to the third region, the abdomen. Like the thorax it is -visibly divided into segments, though the division between them is -not so great. Much difference of opinion exists as to the number of -segments in the abdomen of a typical insect. Some authorities maintain -there are eleven, while others put the number as low as five. This, -however, is theoretical rather than practical. It is enough for us -to know that the number apparently varies greatly, owing to the -coalescence of two or more of the segments. - - [Illustration: - - FIG. 26.--Upper surface of abdomen of typical Beetle.] - -The head in Insects, we have seen, carries the eyes, antennae, and -feeding organs. The thorax bears the legs and wings. The abdomen bears -no appendages, except in some cases, on the last segment; these are -called _cerci_. It may be, however, that the stings of bees and -the ovipositors of saw-flies and other insects are modified appendages. - -On examining the abdomen of Dytiscus we shall probably be struck with -the difference in appearance between the upper and the under surfaces. -The latter is hard, smooth, and shiny; the former, when the wings are -removed, is seen to be covered with felt-like hair. - -Our interest is with the upper surface. Along the abdomen on each -side lie spiracles, stigmata, or openings to the breathing tubes. The -first and last are larger than the rest, and their general form can be -readily made out with an inch magnifier, and with the half-inch we may -get some idea of the detail shown in Fig. 27. - - [Illustration: FIG. 27.--Spiracle of Dytiscus - (magnified).] - -Dytiscus breathes in this way. Floating up to the top of the water, -the end of the abdomen projects above the surface. If one watches the -Beetle the wing-cases will be seen to rise a little. The air retained -by the felted hairs is given off, and a further supply taken in. Then -the wing-cases are lowered again; the Beetle gives two or three strokes -with its swimming legs, and descends below the surface to ramble round -the tank in search of food. - - [Illustration: FIG. 28.--Tracheal tubes (magnified).] - -This air-supply between the wing-cases and the abdomen is taken in at -the spiracles and distributed through the tracheal tubes throughout -the body. These tubes branch and subdivide till they end in small -twig-like vessels comparable to the capillaries of the human body. -They consist of two layers--the inner strengthened by what probably is -a spiral fibre, though Packard believes that, in some cases at least, -it consists of similar rings. But we must not pursue this subject. It -would lead us beyond our appointed limits. - - * * * * * - -Another Beetle fairly common in stagnant waters round London and in -the southern counties is that to which the name Great Water Beetle -(_Hydroph´ilus pic´eus_) of right belongs. This name is sometimes -wrongly applied to Dytiscus, with which its rightful owner has -little in common, except its aquatic habitat. Its scientific name is -_Hydrophilus piceus_; but we shall speak of it as Hydrophilus. - -It is not a very easy matter to take this Beetle with a net, by -sweeping in the ordinary way, for it likes to get into the middle of -a mass of vegetation, where it is sure of a good food supply, and is -probably safe from the attacks of Dytiscus, who not unfrequently makes -a meal of his larger relation. A good plan is to pass the net under a -mass of weed and then shake it to and fro in the water. By this means -any Beetles in the weed will be dislodged from their hiding-places, and -fall down into the bottle. - -They have, in confinement, the same habit of making a snug place -for themselves; and more than once I have fancied that a Beetle of -this species had escaped from the aquarium, when all the time it was -hidden in a thick patch of water-moss. They are practically vegetable -feeders, though Dallas says that they are not such strict vegetarians -as to deny themselves a meal of animal food when they meet with a dead -mollusc or larva in the course of their wanderings. I have never known -them to indulge in animal food, dead or living, but I have known them -refuse it. - -Hydrophilus is the largest British Water Beetle, and, with the sole -exception of the Stag-Beetle, the largest British member of the Order. -Its total length is very little less than two inches, and across the -middle of the back it measures about half as much. It is more slenderly -built than Dytiscus, and the contrast in the size and armature of the -legs is very striking (Fig. 29). There is also a great difference in -their method of progression through the water. Dytiscus moves both legs -simultaneously, while Hydrophilus walks rather than swims, moving one -leg after the other. - -If we cannot collect this Beetle for ourselves--which we should -endeavour to do, if possible--it may be bought of almost any dealer -in what are called ‘aquarium requisites.’ But prices rule higher -for Hydrophilus than for Dytiscus. Bateman says that this species -is rarer than formerly, and that specimens cost from 1_s._ to -2_s._ 6_d._ a pair, ‘according to the dealer and the season.’ -From this I gather that I must have gone to a shop where the prices -were reasonable, for I have never paid more than 6_d._ for a -Hydrophilus, and then have been allowed to pick out a male. At the same -shop I have paid 2_d._ for Dytiscus. - - [Illustration: FIG. 29.--Great Water Beetle. _a_, - male; _b_, female; _c_, larva; _d_, pupa.] - -In keeping this Beetle we shall need a larger vessel than was required -for Dytiscus. (In both cases the aquarium should be covered, for if -food be scarce, and sometimes for other reasons, both these Beetles -may take to flight.) The aquarium should be well supplied with growing -water-weed, but none that is choice or valuable should be put in, for -in moving about over the weed the animal will damage almost if not -quite as much as it eats. This difficulty can be easily got over by -supplying it with anacharis, water-crowfoot, milfoil, or any other -common plant that grows rapidly and is easily procurable. - -The only specimen that I have taken myself was captured a few miles -north of London. It exhibited a strange instance of depraved appetite. -In the large tank into which it was put were growing vallisneria, -frog-bit, and water-crowfoot in plenty. These it was never seen to -touch. The tank, at one time, had been used for newts, and floating -on the surface was a piece of virgin cork. It had served the former -inmates as a kind of island continent, and had never been removed. To -the under side of this the Beetle would moor himself, head downwards, -and nibble away, as if cork were the natural diet of a British Water -Beetle. - -In a few days the Beetle died. It was put into spirit, and soon after -became the subject of a post-mortem. But its strange diet was not the -cause of its death, which was sufficiently accounted for by injuries -inflicted before its capture, probably by a larval or an adult Dytiscus. - -It would be mere waste of time to go over this Beetle and describe it -point by point, as was done with Dytiscus. If what was there written -was of any value, readers will be able to apply for themselves the -method laid down. There are, however, some points of difference to -which it will be well to invite attention. - -It is a good plan to lay specimens of these Beetles side by side -for comparison. Hydrophilus is the larger of the two; and differs in -colour as well as in size. Its hue is black with an olive tinge; and -in certain lights a blue-black metallic gloss may be seen on the outer -margins of the wing-cases. These are marked with faint longitudinal -lines, and each bears three rows of dots running in the same direction. - -The greater length and more slender build of the legs of Hydrophilus -are at once apparent. There is also a marked difference in the tarsal -joints of the fore-legs of the male. The disks and cup-like hairs of -Dytiscus are absent in Hydrophilus, but in their stead the last joint -bears a sub-triangular plate, studded on the inner surface with spines, -which probably serve a similar purpose. A great deal of valuable -information about organs of this kind and their functions will be -found in chapter X of Darwin’s _Descent of Man_. Simmermacher’s -paper[13] should be consulted by all who have the opportunity. Our inch -magnifier will show us these spines quite clearly; and also a curious -little bunch of bristles, which Simmermacher says are probably organs -of touch. - -It is a good plan to take Hydrophilus out of the water, and lay it upon -its back, so that the difference between it and Dytiscus may be clearly -seen. The Beetle should be handled carefully, for on the thorax is a -kind of keel, ending in a sharp spine, which extends over part of the -abdomen. This spine is free, and may easily wound the hands of those -who do not watch the motions of the creature pretty carefully. The fore -part of the abdomen and the thorax are covered with short close hairs, -and when the Beetle is in the water these parts entangle a layer of -air, which gives it the appearance of being covered with quicksilver. - -The two Beetles differ also in their method of exchanging impure for -pure air. Dytiscus, as we have seen, takes in a fresh supply under -its wing-covers behind; Hydrophilus takes in a fresh supply in front, -employing for this purpose the antennae, which apparently do not -function as feelers, as is generally the case. - -When Hydrophilus wants to take in a supply of pure air, it rises to -the top of the water, slowly and deliberately. Unlike Dytiscus, it -is never in a hurry. Then one of the antennae is pushed through the -surface film, thus communicating with the air, which descends to the -hair-covered thorax, whence it reaches the spiracles on the upper -surface of the abdomen. To allow of this the wing-cases are slightly -raised in front. The spiracles in Dytiscus are larger at the posterior -end of the abdomen: in Hydrophilus the largest spiracles are in front. -This is what might be expected, from the method adopted in each case -for procuring a fresh supply of air. - -These Beetles have frequently bred in confinement; but no better -account than that of Lyonnet has ever been given of the operation of -the female in making her cocoon and depositing her eggs. As his account -is not generally available, a condensed translation of it is inserted -with his illustration. - - [Illustration: FIG. 30.--Female Hydrophilus constructing - a cocoon. (After Lyonnet.)] - -Lyonnet[14] wanted to find out how the female made the cocoons (Fig. -30), and this is how he set to work. He put some of these Beetles into -a large aquarium, with a good quantity of water and some duckweed. -On May 31 and the following day he noticed that one of the females -was swimming about in every direction, as if in search of something. -Thinking that this was because she had not the proper materials for her -work, he then put into the aquarium some thread-like alga of a kind -which he had seen attached to some cocoons, and on June 3 the Beetle -began to make a cocoon, but soon gave up the task, apparently because -she was troubled by other aquatic insects which had made a home in this -weed. These intruders were removed, and the Beetle set to work once -more. Lyonnet then noticed that, like a spider, she had her spinning -apparatus at the posterior end of the body. She extended the last -segments slightly, and opened the hindmost one, when he saw a nearly -circular opening, in which was a whitish disk (Fig. 30A, -_a_). On this disk were two little brown tubercles side by side, -nearly at right angles to the longitudinal axis of the body. From each -there projected a blackish-brown conical tube, about a line long, stiff -towards the base, but flexible and elastic towards the tip. These tubes -were the spinnerets, which acted together with a parallel movement, and -from each proceeded a separate thread. - -And this is how she made her cocoon. She lay near the surface of the -water back downwards, the under part of the body and the second and -third pair of legs buried in the thread-like weed. The front legs were -free, and with these she shaped the weed over her abdomen. Then she -spun a covering of white silk against the under side of the weed. While -she was spinning, from time to time she used her front legs to press -and flatten the work against her body (Fig. 30B), giving it -the shape of a flattened arch, to which her body gave the requisite -curve. This, forming the top of the cocoon, was finished in about half -an hour. Then she turned (Fig. 30C), and spun the bottom of -the cocoon, moulding this, like the top, on the curve of her abdomen, -and uniting the top and bottom with silk which she spun. The work -occupied about an hour and a quarter. - -The Beetle then remained nearly in that position for some two hours. At -first she was hidden in the cocoon quite up to the thorax. The body, -however, was withdrawn almost imperceptibly. During this time she was -busy laying her eggs in regular order, with the pointed ends upwards. - -After this she came out of the cocoon, and closed the mouth (Fig. -30D), making the opening smaller by degrees. Then she made a -little mast (Fig. 30D, _b_), of the use of which Lyonnet -admits his ignorance, suggesting, however, that its construction may -serve to use up the silky matter remaining after the work is finished, -lest it should acquire harmful qualities in the body of the Beetle. The -true explanation seems to be that it serves to convey air to the eggs -inside the cocoon. - -On July 17 Lyonnet was rewarded for his patient watching by seeing -a larva come out of the cocoon, and the next day some fifty more -appeared. What he saw and recorded it is in the power of others to see, -if they will imitate his patient observation. - -The Cocktail Beetle, or Devil’s Coach Horse (_Ocypus olens_), is -an excellent specimen of a Land Beetle to examine, for it is of fairly -large size and extremely common. Moreover it does well in captivity, so -that there will be no difficulty in watching its habits in life, and -pickling it for closer examination when dead. - -During the day these animals usually lie concealed under stones or -pieces of earth, coming forth at dusk and during the night in search -of food. Occasionally, however, they may be met with in daylight, -leisurely stalking a smaller beetle or a fly; then with a dash seizing -the victim in their powerful mandibles, which are quite capable of -making an impression on the human skin, as those who handle these -Beetles unwarily will discover for themselves. - - [Illustration: FIG. 31.--Cocktail Beetle. _a_, - larva; _b_, pupa.] - -Nothing of an animal nature comes amiss to them, and if they cannot -capture living prey, they will make a hearty meal off carrion. This is -an advantage to us, for we may feed our captives with dead insects or -with small pieces of meat. - -This Beetle is about an inch long, and of a deep dull black colour. -The head is joined to the thorax by a distinct neck, and the abdomen -is naked, owing to the fact that the wing-cases are very short. Its -wing-cases bear about the same proportion to those of the Margined -Water Beetle that a man’s frock-coat bears to a boy’s Eton jacket. And -this Beetle may be taken as a good type of a group--the Beetles with -short wing-cases (_Brachel´ytra_). - -The attitude of this animal when irritated or alarmed is well depicted -in Fig. 31. It raises its head menacingly and opens its strong -mandibles to their full extent, at the same time turning up the end of -the abdomen, like a scorpion about to sting. From the last segment it -will often put forth a pair of white vesicles, from which is discharged -a volatile liquid of disagreeable odour, that probably acts as a -defence against insect-eating creatures. - -The best way to capture one of these Beetles is to pick it up with what -Kirby calls the ‘natural forceps’--the finger and thumb. It may be -dropped into any convenient receptacle; the small metal boxes in which -vestas are sold will answer the purpose very well. - -My specimen was given me by a friend, who kept it with another in a -round tin box. It lived with me for about three months in a four-ounce -bottle, that measured three inches in height, to the neck, and two -inches in diameter. The bottom was covered to the depth of about an -inch with garden soil, and the top tightly corked, to prevent the -prisoner’s escape. This precaution was necessary; for the inside of -the bottle, though cleaned from time to time, soon became covered with -a coating of earthy particles, which afforded the Beetle a pretty firm -foothold. - -It was an extremely interesting pet, and its struggles to escape -by climbing up the sides of the bottle often afforded me much -entertainment. It seemed to have a glimmering notion that the only -way out was by the top, and knowing nothing of the cork it would rear -itself up against the side, and try to climb up by vigorous movements -of its fore-legs. It would also take advantage of any little lump of -earth projecting about the rest. It had not intelligence enough to make -anything like a mound for itself, though the inequalities were probably -the result of its burrowing under the surface. Its temper was none of -the best, for if it was disturbed with the forceps it would resent it -fiercely. The mandibles would be opened, the abdomen curled up, and out -would come the two vesicles as a means of defence. If the forceps were -put near the mandibles, they would be seized, and the Beetle would hold -on so tenaciously that it has often been lifted out of its bottle in -this fashion. - -It was exceedingly voracious, and was generally fed on garden worms. -After a full meal its increase in size was very evident. This is not to -be taken to mean that insects grow after they have attained the perfect -or imago state, for this is not the case. But when they have had a long -fast, the segments approach each other, and are forced apart when the -creature is gorged with food. If a Beetle of this species were kept -fasting for some days, and then carefully measured, and measured again -after being plentifully supplied with worms or flies, there would be a -difference of some millimetres between the results. - -Dallas has an interesting passage in his _Elements of Entomology_ -respecting the boldness of the larval form, which is worth quoting. -‘I have seen one engaged in a struggle, which lasted about twenty -minutes, with a worm of some five inches in length, the larva being -scarcely more than an inch long. During this contest the little savage -crept under the worm, fixing his mandibles into the creature’s body in -various places, each bite apparently producing a considerable swelling. -Sometimes he would fasten upon the head of the worm, and retain his -hold with the pertinacity of a thoroughbred bulldog, although twisted -about in every direction by the struggles of his intended victim. At -last, however, he seemed to come to the conclusion that he had been -too ambitious in his desires, and went quietly off amongst the grass, -rather prematurely, as it seemed to me, for when the worm began slowly -to leave the field of battle, about an inch of his tail was attached to -the rest of his body solely by the intestine, a union which the jaws of -the larva would easily have dissolved.’ - -I have never seen a fight between a larva and a worm, for the few larva -I have kept have been fed on flies. But the adult Beetle which has once -fastened on a worm cannot be shaken off. It will grip its prey with the -first pair of legs, fixing the claws in the skin, and will finish a -worm three inches long at a meal. - -A dead specimen should be looked over in the way recommended for -Dytiscus, raising the small wing-covers and unfolding the wings. The -spiracles are to be looked for at the sides of the abdomen, in the -groove formed by the meeting of the upper and under plates of each -segment. The short downy hair with which the body is covered should -be noticed, and the front legs are well worth examination. The tibia -or shank is armed with a strong spine, and between this part of the -leg and that which follows it is a notch, through which the Beetle -passes its antennae to clean them from dirt. The peculiar shape of -the joints of the tarsus or foot is very plainly discernible with the -appliances at our command, and by a careful management we may make out -the different kinds of hairs with which four out of the five of these -joints are furnished; some stout and spine-like, others finer, ending -in a pear-shaped bulb. These last probably serve the same purpose as -the sucking-disks of Dytiscus and the tarsal plates of Hydrophilus. - - - - - CHAPTER III - - COCKROACHES; EARWIGS; THE GREAT GREEN GRASSHOPPER; THE - WATER SCORPION; THE WATER BOATMAN; - CORIXA. - - -The next insect to come within range of our pocket lens is the Common -Cockroach (_Blatta orienta´lis_[15]), popularly misnamed the -Black Beetle. We shall have no difficulty in procuring material for -examination. Housekeepers will tell us that these creatures are only -too plentiful. - -In the last chapter we dealt with Sheath-winged Insects--the -Coleop´tera. Cockroaches belong to the Orthop´tera, or Insects with -Straight Wings. The mouth-parts resemble those of Beetles. The chief -differences that mark off the Cockroaches and their kin from the -Beetles are the incomplete metamorphosis which the former undergo, and -the character of the wings. Straight-winged Insects, when they leave -the egg, differ little in shape from the adult, except in the fact that -they have no wings; and these appendages are absent, or so small as -to be useless for flight in many species. When wings are present the -first pair are of little or no use for flight. They are not, however, -hard chitinous sheaths, meeting in the middle line--that is, straight -down the centre of the back--but of a flexible leathery or membranous -substance, and they usually overlap each other at the tips. The hinder -wings are large and nearly semicircular. The principal veins radiate -from the centre to the circumference, like the sticks of a fan, and -when the wings are folded up they lie straight along the upper surface -of the abdomen. It is from this fact that the Order derives its name. - -There are two great groups, or sections, of Straight-winged -Insects--those that run, like the Cockroaches, and those that leap, -like the Grasshoppers. No Straight-winged Insect is aquatic. - -The Common Cockroach, now so abundant, is not a native, but an -importation from Asia; though how it reached this country is not quite -certain, probably by way of Holland. It seems to have established -itself in London by the end of the sixteenth century, and some two -hundred years later we find Gilbert White recording (in or before 1790) -that ‘a neighbour complained that her house was overrun with a kind of -black beetle, or, as she expressed herself, with a kind of black-bob, -when they got up in the morning before daybreak. Soon after this -account I observed an unusual insect in one of my dark chimney closets, -and find since, that in the night they swarm also in my kitchen.... -The male is winged, the female is not, but shows something like the -rudiments of wings, as if in the pupa state.... They are altogether -night insects, _lucifugae_, never coming forth till the rooms are -dark and still, and escaping away nimbly at the approach of a candle.’ - -This description leaves no doubt as to what the ‘black-bobs’ really -were. This name seems to have dropped out of use, and it would be well -if ‘black beetle,’ in the sense of Cockroach, were also allowed to -drop, for the term contains just as many errors as words. - -We may make our first acquaintance with these insects by keeping some -specimens in confinement. A tin box, with a glass lid, will make a -capital dwelling for them. Some paper should be put in, for them -to hide in away from the light, and there can be no difficulty in -providing them with food. ‘Bark, leaves, the pith of living cycads, -paper, woollen clothes, sugar, cheese, bread, blacking, oil, lemons, -ink, flesh, fish, leather, the dead bodies of other cockroaches, -their own cast skins and empty egg-capsules, all are greedily -consumed. Cucumbers, too, they will eat, though it disagrees with them -horribly[16].’ - -We have Dr. Sharp’s authority for the statement that in confinement -these insects are rather amusing pets, as they ‘occasionally assume -most comical attitudes, especially when cleaning their limbs. This they -do somewhat after the fashion of cats, extending the head as far as -they can in the desired direction, and then passing a leg or an antenna -through the mouth; or they comb other parts of the body with the spines -on the legs, sometimes twisting and distorting themselves considerably -in order to reach some not very accessible part of the body[17].’ - -The prejudice against these insects is, however, so strong, that most -people will prefer to examine dead rather than living specimens, on -account of the disagreeable odour of the latter. This odour is due to -a fetid excretion from the mouth, and if the specimens are killed by -dropping them into boiling water, this will be discharged, and after a -little while they may be taken out with a pair of forceps, and put into -spirit for preservation. If they are dropped alive into spirit, the -excretion will communicate its strong scent to the preserving medium, -and this should be changed before the insects are examined. - -From Fig. 32 we may get a general idea of the appearance presented by -a male or female, lying back upwards in a small glass dish, ready for -examination with the pocket lens. The female may be distinguished at a -glance by her wingless condition--only rudiments of wing-cases being -present, and no wings--and her broader abdomen. In life she does not -stand so high upon her legs as does the male, and her abdomen trails -along the ground. The male does not acquire his wings till the last -moult. - - [Illustration: - - _Female._ _Male._ - - FIG. 32.--Cockroaches.] - -As the Cockroach lies back uppermost in a glass dish, the head is -almost concealed. This is especially the case, unless the insect is -flattened out in some way, or pinned down to a piece of weighted cork. -There will thus be, apparently, two, instead of three main divisions. -This arises partly from the fact that the head is deflexed, or bent -down so that the mouth is turned towards the rear, and partly because -the first segment of the thorax bears a chitinous shield, roughly -semicircular, which covers so much of the head as would otherwise be -visible. - -The difficulty, however, may be easily got over, by reversing the -position of the insect, and raising the head with a needle. The -antennae will attract attention by their great length. In the male -insect they exceed, while in the female they fall a little short of, -the total length of the body. They are well worth examination. Even a -low power will show that they consist of a number of joints--usually -from seventy-five to ninety. The three basal joints are much larger -than the rest, and in the female the third basal is nearly as long as -the first. All these joints are thickly set with stiff hairs directed -forwards. At the outer side of each antenna is a compound eye, and on -the inner side is a pale spot, the _fenestra_, which in the males -of some foreign Cockroaches is replaced by a simple eye. - -If Cockroaches are kept in confinement, and forced out into the light, -the constant motion of the antennae will satisfy the observer that they -are of great use to their owners. By means of these organs they not -only discover their food, but become by some means, probably by the -motion of air-waves, aware of danger that threatens them. Belt, in his -_Naturalist in Nicaragua_ (p. 110), speaking of the Cockroaches -that infest houses in the tropics, says, ‘They are very wary, as they -have numerous enemies--birds, rats, scorpions, and spiders; their long, -trembling antennae are ever stretched out, vibrating as if feeling the -very texture of the air around them; and their long legs quickly take -them out of danger.’ It is not given to every one to visit the tropics, -but we may all use our eyes in observing the common insects that abound -in our country, and in doing this we shall strengthen the habit of -observation, and very often find confirmation of what we read of the -habits of insects in distant lands. - -Sir John Lubbock[18], in treating of the sense of smell in Insects, -says that ‘Plateau put some food of which cockroaches are fond on a -table, and surrounded it with a low circular wall of cardboard. He then -put some cockroaches on the table: they evidently scented the food, -and made straight for it. He then removed their antennae, after which, -as long as they could not see the food, they failed to find it, even -though they wandered about quite close to it.’ - -The large kidney-shaped compound eyes are sure to attract attention. -It is worth while to take out and break up an eye, gently washing out -the pigment. If we do this, and then examine it with the pocket lens, -we shall have some idea of the multiplicity of lenses in the eye of a -Cockroach, each of the six-sided facets being a lens. - -Next come the mouth parts, which may be run over very quickly, for -those of Beetles are formed upon the same plan, and from this primitive -plan are derived the mouth parts of all other Insects, of whatever -character they may be. To examine the mouth organs the insect must be -turned on its back, and the _labrum_ (_a_), or upper lip, -raised with a needle, so as to allow of a general view of the rest. -Then the jaws or mandibles (_b_) may be picked out with a needle. -These jaws are strongly toothed, and work from side to side, and it -is easy to see that they are very efficient organs. The lower jaws -(_c_), or _maxillae_, lie below, and are compound organs, -each being made up of several parts--the base, called the _cardo_ -or hinge (not shown in the illustration, but connected at right angles -by a joint with the lower part, the _stipes_). From the stipes -rise the _galea_, or helmet, on the outer side; and, on the -inner side, the _lacinia_, to which the name maxilla is often -applied, though it properly belongs to the whole. At the base of the -_galea_ is inserted the five-jointed maxillary palp, thickly set -with hairs, and probably an organ of touch. - - [Illustration: FIG. 33.--Mouth parts of a Cockroach.] - -By examining the maxillae (_c_) before they are separated, and -comparing them with the _labium_ (_c_) or under lip, which closes the -mouth from below, it will be evident that there is no slight similarity -between them. Nor is this strange: for the under lip consists of the -second maxillae joined at their bases, which form the _submentum_ (_s_) -and _mentum_ (_m_). (The former is the small, the latter the large -white basal portion; the vertical line in the illustration shows the -mental suture, and should be traced in the dead insect.) The organs in -the centre constitute the _ligula_; and on each side of the labium is a -three-jointed palp (_labial_), like that on the maxillae, thickly set -with hairs, and with a similar function. It is well to work over the -mouth parts a few times till the relation between the maxillae and the -labium is seen and understood. The internal tongue (_d_) is attached to -the inner side of the labium. - -Now, still working on the under side of the insect, the three segments -of the thorax are to be made out, and one cannot fail to notice the -great size of the first joint (the _coxa_) in all the legs, and -that these joints seem to serve as shields to protect the under side -of the thorax. Then the different parts of the legs should be traced, -and compared with Fig. 23 on p. 44. The spiny armature of the tibiae is -to be noticed, as are the claws, between which is a projecting lobe, -though this is absent in immature specimens. We shall find that the -appendages of the thorax are the same as in the Margined Water Beetle. -It is well to take as little as possible on trust, and to verify -everything that we possibly can. - -Now we may reverse the position of our subject, and having cut off -the wing-cases, which are technically called _teg´mina_, examine -the wings. These may be gently unfolded with a needle or a camel’s -hair brush, when the longitudinal method of folding will be clearly -seen, and the difference of the veining from that of the wings of -the Margined Water Beetle will be apparent. A female should also be -examined, and the small tegmina cut off, so as to see that not even the -rudiments of wings are present. - -The Cockroach breathes like other adult Insects, and the spiracles -are ten in number--two on the thorax and eight on the abdomen. The -thoracic spiracles may be pretty readily seen, but those on the abdomen -are not so easy to make out. But by cutting away, with a fine pair -of scissors, the edges of the plates that cover the upper and under -surfaces of the abdomen and the membrane that unites them (Fig. 34), we -may discover them as the open ends of small tubes. While dealing with -the insect in this fashion, it will be easy to take out a piece of the -tracheal tube, which may be compared with Fig. 28. - - [Illustration: FIG. 34.--Cockroach, showing Spiracles.] - -The abdomen consists of a series of rings or segments, the exact number -of which is rather difficult to decide, from the fact that some are -concealed and others altered in form. Dr. Sharp[19] says that ‘it is -considered that ten dorsal and ten ventral plates exist, though the -latter are not so easily demonstrated as the former.’ In the male, ten -above (dorsal) and nine below (ventral), and in the female two less in -each case, may be made out without dissection. - -From the sides of the tenth segment two organs, the _cerci_ -(Fig. 35, _a_), are given off, one on each side. These may be -distinguished from the styles of the males by their presence in both -sexes. Our inch lens will show that each cercus consists of sixteen -rings. If we use the half-inch, we shall see that each ring is set with -hairs of different lengths. - -When we have got so far it may be well to compare the structure of -a _cercus_ with that of an antenna (p. 67). In each we have a -succession of jointed rings giving flexibility to the organ, and the -rings in each case are studded with hairs. It has been shown pretty -conclusively--and we may verify the experiments--that the antennae are -sense-organs. Are we not justified in coming to the conclusion that, -since the antennae and the cerci resemble each other in structure, -they also resemble each other in function? If the Cockroach receives -sensations by means of the antennae, is it not probable that it also -receives sensations by means of the cerci? - -Having worked over the Cockroach from the outside, it will be -advantageous to get some acquaintance with its internal anatomy. -This is not a difficult matter. The specimen is to be pinned down, -under water, with its back uppermost. The wings having been removed, -a longitudinal cut is to be made down the centre from the posterior -part of the abdomen to the back of the head, and the two sides of the -integument turned back. Or the junction between the upper and lower -plates on each side may be cut through with a cutting needle, and the -whole integument removed. - -The first task is to clear away the fat-body, a whitish substance -which overlies the chief organs of the body. When this is picked to -pieces and floated off the digestive system will be exposed. After -this has been worked over a few times there should be no difficulty in -dealing with similar parts in other Insects. At the back of the head -lies the gullet or oesophagus leading into the crop (_c_), at the -base of which lies the gizzard (_g_). The interior of this organ -is furnished with six strong chitinous teeth, with small ridges of -the same substance between them. Towards the posterior end are six -cushions, all set with fine bristles. Behind this comes the stomach -(_v_), into which open seven or eight tubes, closed at one end, -and between it are the Malpighian tubes, which are concerned in the -process of excretion. The small intestine (_co_) succeeds, and -behind this is the rectum (_r_). - - [Illustration: FIG. 35.--Alimentary Canal of Cockroach.] - -It will be interesting to separate the gizzard from the crop (_c_) -and stomach (_v_) and break it open with a couple of needles, so -as to examine the teeth, which will be more easily made out if the -opened organ be allowed to soak for a time in a solution of caustic -potash. - -Similar teeth-like processes are found in the gizzards of many other -Insects, and their presence has given rise to some strange ideas. -Swammerdam[20] says, ‘I preserve also the threefold stomach of a -locust, which is very like the stomach of animals that chew the cud, -and particularly has that part of the stomach called Echinus[21] very -distinctly visible. I do not, therefore, doubt but locusts chew the -cud, as well as the animals just mentioned. Indeed, I persuade myself -that I have seen this.’ - -Somewhat similar teeth-like processes exist in the Lobster, the Crab, -and the Crayfish. ‘Professor Plateau has expressed a strong opinion -that neither in the stomach of Crustacea nor in the gizzard of Insects -have the so-called teeth any masticatory character.’ He adopts -Swammerdam’s comparison, but considers them strainers, not dividers of -the food[22]. - -We may be fortunate enough to meet with some specimens of the American -Cockroach (_Periplane´ta america´na_, Fig. 36), a much larger -species, which has established itself in some few places in this -country. At the Zoological Gardens, Regent’s Park, it is abundant, and -has almost, if not entirely, driven out the common form. Mr. Bartlett -believes that it was introduced in cases in which animals have been -sent over from America. Both sexes are winged. They not only possess -organs of flight, but use them. If one visits the Gardens, there will -be no difficulty in getting specimens; and it is interesting to compare -the points of agreement in and of difference between this animal and -our common form. - - [Illustration: FIG. 36.--American Cockroach (male).] - -The Earwig (_Forfic´ula auricula´ria_) is common enough to furnish -us with plenty of specimens on which we may employ our pocket lens. Any -garden in the summer months will yield an ample supply. Earwigs, like -Cockroaches, are light-shunning insects, and love to hide themselves in -the corollas of flowers; and it is probably from their habit of seeking -to conceal themselves that they have acquired their bad reputation--by -no means confined to our own country--of creeping into the ears of -persons lying asleep, and causing death by getting into the brain. Such -an occurrence is beyond the bounds of possibility. No insect of this -size could pass the drum of the ear. - -We may easily keep these insects and observe their movements, if we -put them into a wide-mouthed glass bottle and supply them with food. -They are extremely fond of the flowers of the dahlia; but a dahlia -would offer too many hiding-places, so we will put into the bottle some -nasturtium flowers, or any others with a bell-shaped corolla. - -If we get a colony in spring we may watch the care of the female for -her eggs. According to Kirby and Spence[23], ‘she absolutely sits -upon her eggs, as if to hatch them--a fact which Frisch appears first -to have noticed--and guards them with the greatest care. De Geer -(_Mémoires_, iii. 548) having found an earwig thus occupied, -removed her into a box where was some earth, and scattered the eggs in -all directions. She soon, however, collected them one by one, with her -jaws, into a heap, and assiduously sat upon them as before. The young -ones, which resemble the parents, except in wanting elytra and wings, -... immediately upon being hatched creep like a brood of chickens -under the belly of the mother, who very quietly suffers them to push -between her feet, and will often, as De Geer found, sit over them in -this posture for some hours.’ Mr. Kirby adds: ‘This remarkable fact I -have myself witnessed, having found an earwig under a stone which I -accidentally turned over, sitting upon a cluster of young ones, just as -this celebrated naturalist has described.’ - -Like the Cockroaches, Earwigs undergo an incomplete metamorphosis. -When the young leave the egg they resemble their parents, as may be -seen from the immature forms represented in Fig. 37. The resemblance -becomes greater at each successive moult. - - [Illustration: FIG. 37.--Larva and Pupa of Earwig.] - -In working over these insects, the forceps, or pincers, at the end -of the abdomen will attract attention. They are found throughout the -family, but little is known of their function. It is said that they -are used to aid in folding the wings, and tucking them under the -wing-covers. This can scarcely be their only function, for they are -found in species that have no wings. Probably they serve as organs -of defence and, to some slight extent, of offence. When the abdomen -is curled up, these forceps certainly give the insect a threatening -appearance. They cannot, however, do much harm. - -These forceps differ in shape in the male (Fig. 38) and female, the -blades being almost close together in the latter. In the males they -differ considerably in size. Of 583 mature males taken in one day in -the Farne Islands, and examined by Messrs. Bateson and Brindley, the -forceps varied in length from 2·5 mm. to 9 mm.[24] These are called -respectively ‘low’ males and ‘high’ males. The latter are in all points -larger than the former, and have been described as a separate species, -‘but it was impossible to get reliable measurements of the total -length, owing to the fact that the abdominal segments telescope into -each other’ (cf. p. 30). - -After examining the antennae and dissecting out the mouth organs, the -peculiar overlapping or imbrication of the plates of the abdomen -should be looked for; and on the membrane that connects them the -spiracles may be detected. - -The wings and the complex method of folding have led some systematists -to rank the Earwigs as an Order, while some others rank them as a -Sub-order. For the present, at any rate, we need not concern ourselves -about this. It is enough for us to know that they are closely related -to the Orthop´tera. - -As we look at the Earwig from above, the wing-cases recall to our mind -those of the Devil’s Coach Horse (Fig. 31), though there is one great -difference. From beneath those of the Earwig project two small leathery -pieces which are absent in the Beetle. These pieces are not, as one -might imagine, at the tips of the wings, but on the front margin, about -halfway down, and is indicated in the illustration by the shading -between the extremity of the wing-case and the crease-mark at _a_. - - [Illustration: FIG. 38.--Earwig (male).] - -From the illustration we may understand how the Earwig opens and closes -its wings. From the point _a_ veins, which are thickened about -halfway down, radiate to the hinder edge of the wing, and a little -beyond the thickening they are connected by a vein which runs parallel -with the hinder edge. These radiating veins are brought together, so -that there is a fan-like closing, like that of the Cockroach, but from -a different centre. The wing is then folded back at the place where the -veins are thickened, and then there is a second transverse fold at the -point _a_, so that the only part of the wing now visible is the -leathery patch, which projects beyond the wing-case when the wing is -tucked away. - -It is not difficult to unfold the wing of a dead specimen, under water, -using a needle and fine brush. Mr. E. A. Butler[25] recommends a simple -but excellent plan for unfolding and preserving the wing, by gumming -it, with the upper surface downwards, to a piece of card, and gradually -unfolding it and fastening it down. This is not so easy as it may seem, -but with patience and perseverance success will be obtained; and a -similar method may be adopted with the wings of other Insects, which -may be mounted in this way without any trouble. Thus they may be easily -preserved for examination at a future time, or for comparison with the -wings of other Insects. - -It is rather remarkable that an insect like the Common Earwig, which -very rarely takes to flight, should have such a complex method of -folding its wings. Dr. Sharp says that though the Earwig ‘is scarcely -surpassed in numbers by any British insect, yet it is rarely seen on -the wing. It is probable that the majority of individuals of this -species may never make use of their organs of flight, or go through the -complex process of folding and unfolding them.’ - -Let us choose our next example from the Leaping Orthop´tera. They may -be distinguished at a glance from their relatives that run, but do not -leap, by the peculiar structure of the third pair of legs. These are -much longer and stouter than the other two pairs, and the thigh is very -muscular. This insect is a very good type of the family Locus´tidae, to -which, however, none of the insects popularly called ‘locusts’ belong. -They are included in another family (_Acridi´idae_), where the -common British Grasshoppers are also placed. The Locustids and the true -locusts may be distinguished by the difference in their antennae: in -the latter these organs are short, in the former they are very long and -delicate. - -The Great Green Grasshopper (_Locus´ta viridis´sima_) (Fig. 39) is -fairly common all over the country, but often escapes observation from -the fact that its hue corresponds so nearly to that of the foliage on -or among which it lives. One specimen taken in a Devonshire lane gave -me a great deal of trouble before it was secured and transferred to -a small tube. It was perched on a leaf when I first saw it, and as I -approached it leaped away. Though I was certain it had not gone far, -it was some little time before I discovered it, and got near enough -to grasp leaf and insect, in time to prevent the latter from taking -another jump. - -This insect may be kept alive in confinement for a considerable time, -and will do fairly well on a diet of leaves and fruit, though it will -not refuse an occasional meal of flesh. Dr. Sharp says that a specimen -in confinement ‘mastered a humble-bee, extracted with its mandibles -the honey-bag, and ate this dainty, leaving the other parts of the -bee untouched.’ It is said that if two be placed together in a box -they will fight most desperately, and that the victor will make a meal -off the body of its victim. De Geer witnessed a case of this kind in -a closely allied species that is found in Sweden. Its specific name -signifies ‘wart-eater,’ and commemorates the fact that the peasants -incite these insects to bite their warts, firmly believing that warts -once bitten speedily disappear, and do not grow again. Westwood says -that one of these insects actually devoured part of its own leg that -had been broken off accidentally. When the creature was seen at night -the detached leg was whole; in the morning about half of it had been -eaten. - - [Illustration: FIG. 39.--Great Green Grasshopper - (female).] - -It is well to get specimens of male and female insects. We shall -require the former in order to examine the sound-producing apparatus, -which the females do not possess; and the latter for the sake of the -ovipositor--a long scimitar-like organ by means of which the eggs are -deposited. Let us take the female first. The length, including the -ovipositor, is a little under two inches, and the antennae will measure -about as much more. The wing-cases do not lie flat upon the back, as do -those of the Cockroach, but in a slanting position, like the sides of -a roof, forming a ridge in the centre. The head is not bent back, as -in the Cockroach, nor does it project in front, as in the Beetles, but -the front is almost vertical. The armature of the mouth is strong, and -of the same pattern as that of the Cockroach. The hood--so the upper -covering of the thorax is called--is of a peculiar shape, somewhat like -that of a saddle. The wing-cases and wings, with their folding, will -offer little difficulty. Next we may examine the cerci, and contrast -them with those of the Cockroach and with the forceps of the Earwig. -Last of all, the ovipositor must be examined, and its structure made -out, so far as the means at our command will allow. - -Apparatus of this kind for placing eggs in positions favourable to -their development is by no means confined to these insects, for -examples may be found in other Orders. Sirex, the so-called Tailed -Wasp, has a long straight one, which is often supposed to be a sting, -and the insect itself is not unfrequently taken for a gigantic wasp or -hornet. - -When the ovipositor of our subject is looked at with the unassisted -eye, it appears to consist of two curved blades placed side by side, -with an internal groove on each. The apparatus, however, is not quite -so simple: it is made up of six chitinous rods, of which four--the two -above, and the two central ones--are developed from the ninth segment -of the abdomen, while the two lower ones spring from the eighth. It is -not difficult to test these statements. Specimens are plentiful; and as -the ovipositor in this insect is large, and easily broken up into its -component parts, it may well serve as an introduction to the study of -these organs in other Insects--the Saw-flies, for example. - -When the insect is about to deposit her eggs, she selects a spot where -the soil is light, and bending the ovipositor nearly at a right angle -to her body, thrusts it into the ground as far as possible. Then, by -a muscular effort, the plates of the ovipositor are separated, and -several eggs travel down the passage formed by the central pair of rods -into the hole. This is repeated time after time, till the operation of -egg-laying is completed. This takes place in the autumn, and the young -emerge from the eggs in the spring. When they come out they are tiny -copies of the adults; but they do not acquire wings till after several -months. The ovipositor of the female appears after the second moult, -and till this organ is developed no difference is apparent between the -young insects. - -The chief interest of the male insect lies in its wings, for the first -pair (the _teg´mina_) are the organs with which it produces its -‘love-songs.’ Kirby comments on the fact that Lichtenstein, in the -_Linnaean Transactions_ (iv. 51), ‘draws attention to the eye-like -area in the right wing-case of the males of this genus,’ adding that -that author seemed ‘not to be aware that De Geer had noticed it before -him, as a sexual character; and also, with good reason, supposed that -it assists these animals in the sounds they produce.’ - -This is how De Geer (_Mémoires_, iii. 429) describes the -sound-producing apparatus of the Great Green Grasshopper: ‘In our -male grasshoppers, in that part of the right elytron which is folded -horizontally over the trunk, there is a round plate of very fine -transparent membrane, resembling a little mirror or piece of talc, of -the tension of a drum. This membrane is surrounded by a strong and -prominent nervure, and is concealed under the fold of the left elytron, -which has also several prominent nervures answering to the margin of -the membrane or ocellus. There is every reason to believe that the -brisk movement with which the grasshopper rubs these nervures against -each other produces a vibration in the membrane, augmenting the sound. -The males in question sing continually in the hedges in the months of -July and August, especially towards sunset, and part of the night. When -any one approaches they immediately cease their “song.”’ - -It is probably unnecessary to do more than remark that the noises made -by Insects do not correspond to the voices of the higher animals. ‘For -no insect, like the larger animals, uses its mouth for utterance of -any kind: in this respect they are all perfectly mute; and, though -incessantly noisy, are everlastingly silent[26].’ - -Our plan with these wings is to first verify the fact of their bearing -these talc-like spots, the serrated nervures on the right and the -rudimentary file on the left elytron. The sound is produced by rubbing -the base of the left elytron against that of the right. A recent author -compares this insect to a fiddler, and says that the left tegmen is the -bow and the right the fiddle. - -The last point to examine is the ear. It seems strange to say that -these insects have ears in their legs; but though some of the older -entomologists regarded these structures in the tibiae of the first pair -of legs as nothing more than resonators or sound-boards to intensify -their chirping, there is no doubt that they are really organs of -hearing. Much interesting information on this subject will be found in -Sir John Lubbock’s _Senses of Animals_. - - [Illustration: - - FIG. 40.--Tibial ear of Great Green Grasshopper.] - -These oval patches are plainly distinguishable by the unassisted eye, -and correspond in function to the tympanum or drum of the human ear. -The air-supply to the tibiae is distinct from that of the rest of the -body, and is derived from a large orifice on each side of the first -segment of the thorax. These orifices may be seen by removing the -‘hood.’ Indeed, they cannot escape observation. From these orifices an -air-tube passes to each leg, dividing into two branches in the tibia -and reuniting below the drums. - -Dr. Sharp[27] says that ‘although the tibial ears of the Locus´tidae -are very perfect organs, there is great difficulty in deciding on the -exact nature of their functions. They would appear to be admirably -adapted to determine the precise locality from which a sound proceeds -... for the legs can be moved in the freest manner in every direction, -so as to bring the drum into the most direct line of the vibrations. -But as to what kinds of vibrations may be perceived, and the manner -in which they may be transmitted to the nerves, there is but little -evidence.’ - -The next Order from which we shall choose examples will be the -Hemip´tera, containing the Land and Water Bugs and some other forms. -Our chief concern, however, is with the Water Bugs. In this Order the -metamorphosis is incomplete; the mouth is adapted for sucking the -juices of plants and animals; and there are usually four wings. In the -Land and Water Bugs, part of the fore wings is harder than the hind -wings; in the other winged members of the Order both pairs of wings are -membranous. The front wings are called hemel´ytra or halfel´ytra, to -distinguish them from the el´ytra or wing-cases of Beetles, which are -chitinous throughout. Fig. 41 shows the hemel´ytron and hind wing of a -Land Bug, and the names given to the different parts of the front wing. - - [Illustration: FIG. 41.--A Land Bug (magnified). - _a_, corium; _b_, clavus; _c_, membrane.] - -The Water Scorpion (_Nepa cine´rea_) is not difficult to procure, -or to keep in confinement when it is caught. It would be straining -language to call it a handsome creature, yet it well deserves careful -study, on account of the wonderful modification of the first pair of -legs, and it is from the resemblance of these to the pedipalps of the -scorpion that the insect derives its popular name. Its length is about -an inch and a quarter, from the tip of the beak, or rostrum, to the end -of the breathing-tube. Its greatest width is a little over a quarter of -an inch (Fig. 42). The general hue harmonizes well with the mud, but -the upper surface of the abdomen is a warm red, ‘and is thick set with -hair, so as to afford a very agreeable sight.’ - - [Illustration: FIG. 42.--Water Scorpion.] - -It is extremely common in shallow pools, and its favourite haunt is -near the shore, where it will lie, almost buried in the mud, with its -raptorial legs elevated, ready to seize on any passing insect, and its -breathing-tube just pushed through the surface-film. I learnt this -habit of the insect on the first occasion on which I tried to collect -specimens of it. I had been told that a certain piece of water swarmed -with Water Scorpions. This, I afterwards found, was quite correct; -but though I worked the pond from end to end, a single specimen was -all that rewarded my labour. Whilst transferring the insect from the -net-tube to the bottle for transport, a stranger joined me, and kindly -volunteered his assistance. He had no collecting tackle, but in about -a quarter of an hour he brought at least a dozen good specimens in the -bottle he had borrowed. - -It was natural to inquire to what his success was due. He told me that -it was his first attempt at collecting, but that just before joining -me he had noticed the ends of the breathing-tubes sticking out of the -water. This excited his curiosity, and on moving the mud with his -walking-stick, the insects were seen to crawl away slowly. When he -saw me transfer the Water Scorpion from the net-tube to the bottle, he -immediately recognized it. Then he courteously offered his help, for -which, of course, I was grateful. - -We may keep the Water Scorpion alive for a considerable time in a small -bottle of water, in which is some growing weed. If we watch it moving -about, we shall see that the front legs are used for locomotion as well -as for seizing prey. Some authors doubt this. Any one may settle the -question for himself, if he will put one of these insects into a small -bottle with plenty of weed. Generally, however, the insect uses only -the second and third pairs for walking, the first pair being raised and -directed forward, with the tarsus bent at an angle (Fig. 42). Even when -it does use its front legs for locomotion, the action is not that of -walking; the insect employs these limbs to pull itself along in a sort -of ‘hand-over-hand’ fashion, but on a level surface it uses the first -pair in the same way as it does the other two pairs. - -Its habit of burying itself in the mud may also be watched with very -little trouble. A common pudding-basin will make an excellent aquarium -for this purpose. The bottom is to be covered with garden mould and -vegetable _débris_, mixed with a few stones. The whole mass should -be arranged unevenly, so that when water is added it may not form one -sheet, but a series of small shallow pools. Very little duckweed will -serve to keep it sweet. It only remains to drop in the Water Scorpion. -Before long it will accommodate itself to its new surroundings, and so -bury itself that it will be no easy task to discover it. - -An aquarium of the kind described stands at present on my -writing-table. Many have been the inquiries as to what kind of creature -lived therein; and more than one old hand at collecting has failed to -find the insect. It is always safe to look round the sides of the basin -for the breathing-tube; if it is not detected in this situation, a -glance along the surface of the tiny pools will probably show a break -in the film. The Water Scorpion will not be far off. - -That the insect really does cover itself with mud may be demonstrated -by transferring it from the aquarium described to any shallow vessel, -and allowing a fine stream of water--say, from a dipping-tube--to fall -gently on it. The mud will be washed away, and in a few seconds will -settle at the bottom. - -It is well to keep such an aquarium covered, for the Water Scorpion has -no mean power of flight. A circular plate of glass, which may be bought -for a few pence, makes the best cover, but a piece of fine muslin -fastened round the rim of the basin will do. Swammerdam says, ‘These -Water Scorpions live all the day in the water, out of which they rise -about the dusk of evening into the air, and so flying from place to -place, often betake themselves in quest of food to other waters.’ Then -follows a deduction which shows how far he was in advance of his time: -‘This affords us a satisfactory reason for the great number of insects -that immediately appear in the smallest collections of water, since -they may very well get thither when it is dark, so that the opinion -which ascribes to putrefaction the power of forming insects, &c., must, -by this instance of the Water Scorpion’s nocturnal transmigrations, -appear more and more frivolous and unnecessary.’ - - [Illustration: - - FIG. 43.--_A._ Water Scorpion. _a_, rostrum; - _b_, wing-cases; _c_, wings; _d_ _d_, - second and third pairs of legs; _e_, raptorial legs (the - first pair); _f_, spine forming breathing-tube; _g_, - parasitic mite. _B._ Portion of an oviduct containing eggs - (magnified). _C._ An egg (magnified). _D._ Parasitic - mite. _a_, head; _b_, eyes; _c_, legs; _d_ - _d_, legs (seen from under surface). (After Swammerdam.)] - -No larva or other animal that is of any value should be kept in the -same aquarium with the Water Scorpion. Dr. Hill, who annotated the -English edition of Swammerdam, says, ‘There is not perhaps in all the -animal creation so outrageous or fierce a creature against those weaker -than itself as the Water Scorpion. It destroys, like the wolf among -sheep, twenty times as many as its hunger requires.’ The Rev. G. C. -Bateman placed one in a saucer with a tiny minnow; ‘but no sooner did -the little fish swim within reach of the fore-legs of the scorpion -than it was seized by them, and pressed against the hungry creature’s -rostrum.’ It seems to be particularly fond of Asellus, the water -woodlouse. I have often taken dead specimens of this crustacean, sucked -completely dry, from between the raptorial legs of the insect. One -specimen was so thoroughly cleaned out that it was mounted just as it -was, the only preparation being a brief soaking in spirit. - -In examining the head the eyes may be readily distinguished, and on -pressing the rostrum or beak with a needle, the proboscis will be -forced out, just as one may force out the sting by pressing the abdomen -of a bee or a wasp. In this group the antennae are three-jointed and -concealed. When one begins to look for these organs he will probably -come to the conclusion that the concealment is highly effectual. - -A very simple method of finding them in a spirit specimen is to take -the insect between the thumb and index finger of the left hand, holding -it up to the light in such fashion as to keep the first pair of legs -well clear of the head. Then, with a needle held in the right hand, -raise the thorax till it lies in the same plane as the body. Each -antenna lies in a groove beneath the eye. Gentle manipulation with the -needle will lift them out, so that they may be clearly seen, not only -with the hand magnifier, but with the unassisted eye. Or the insect may -be pinned down under water instead of being held in the hand, and the -antennae lifted or brushed out of the groove. - -It will greatly simplify matters if, before attempting to raise the -wings, the fact is borne in mind that the tip of the right wing-case -lies over that of the left. It is perhaps as well to remove the -wing-case altogether by inserting a needle under it, and gently raising -it, using a little pressure in an outward direction. It will then be -quite time to raise the wing and to see the method of folding and -unfolding. - - [Illustration: FIG. 44.--Raptorial leg of Water - Scorpion.] - -In Fig. 44 we have a representation of the raptorial (front) leg -of this insect. This leg should be compared with the legs of other -Insects--not in pictures only, but in actual specimens--that we may see -how, while the general plan is preserved, different joints are modified -to suit the special function of this limb--that of taking prey. (See -also Fig. 43.) - -The thigh (_f_) is the largest joint, for the obvious reason that -it contains the muscles that work the tibia and tarsus, which together -form a kind of knife-blade, shutting down into a groove in the thigh, -which may very well be compared to the handle of a pocket-knife. This -description, however, is not to be taken on trust. It is not enough -to read about the groove: we must see it for ourselves, raise the -‘knife-blade’ from the groove, and press it down again, and pass the -needle along the groove. If we examine the interior of the groove, we -shall find that there is a projection along the bottom, so that a cross -section would appear like this--W[image]. The inner portion of the -tibia is also grooved; so that when once the prey is seized by this -powerful limb, it has no chance of escape. The tarsus (_tar_) -is not clearly distinguished from the tibia (_tib_) in the -engraving, but it may be distinctly seen as a claw-like appendage in a -living or dead specimen. - -The breathing-tube remains to be examined. It may be detached from the -body for more convenient manipulation. When this is done, the tube will -be seen to consist of two pieces, each grooved on the inner side and -set with hairs, which, as they interlock, prevent the entrance of water. - -A somewhat similar arrangement occurs in the proboscis or tongue of -butterflies. There is perhaps a closer parallel in the antennae of -the masked crab, which, under certain conditions, form a kind of -breathing-tube, each antenna being joined to its fellow by the hairs -with which it is set. - -There are two other Water Bugs which lend themselves to our purpose -very well. Each is popularly called Water Boatman, though that name is -better confined to Notonecta, because the insects of this genus ‘row -themselves about on their backs with their long feathered legs.’ In the -United States they are called Water Cicadae, from the shrill noise they -make, probably by rubbing the fore-legs together. - - [Illustration: FIG. 45.--Water Boatman.] - -In Fig. 45 the Water Boatman (_Notonec´ta glauca_) is represented -as seen from above--a position in which we shall rarely discover it, -if we keep it in a small aquarium. In Fig. 46 the same insect is shown -swimming on its back, or in the position it assumes when taking in a -supply of air. The end of the abdomen and the tips of the feet rest -against the surface-film; and at the slightest alarm a vigorous stroke -of the last pair of legs sends the insect to a place of safety. From -the way in which these insects habitually swim, Mouffet came to the -conclusion that it was probable men learned the art of swimming on -their backs from them. - - [Illustration: FIG. 46.--Water Boatman swimming.] - -Active as the Water Boatman is, it often falls a victim to the Water -Scorpion, if both are kept in the same aquarium. I learnt this fact by -experience, for having put two Water Boatmen into a small tank in which -was a Water Scorpion, I found both the former dead in the morning. It -was evident that their destroyer had had a good meal. - -The only point to which attention need be called in examining the Water -Boatman is its method of taking in a supply of air. In looking at a -dead specimen we shall see a ridge or keel running down the middle of -the under side of the abdomen, and fringed with hair on each side. -A similar fringe runs along each side of the abdomen, thus forming -two passages along which the air taken in at the end of the body is -conveyed to the spiracles, the largest of which are on the thorax. - -Corixa (Fig. 47) swims with its back uppermost, and when kept in the -aquarium may generally be seen foraging for small creatures--larvae or -worms--among the sediment at the bottom. Bateman, who kept a number -of these insects, says that he fed his specimens on garden worms and -pieces of raw meat. Mine have always foraged for themselves, and done -very well without feeding. They may often be seen to rub the short -fore-legs alternately across the front of the head, probably for the -purpose of producing a call-note. I have often watched them at this -practice, but have never been able to detect any sound. The defect is -evidently in my sense of hearing, for the sounds rest on undoubted -authority, and are coincident with the rubbing of the fore-legs across -the head. - - [Illustration: FIG. 47.--Corixa, with wings expanded.] - -Where sound-producing organs exist it is more than probable the -capacity for receiving sound-impressions also exists. Graber made some -interesting experiments to test the sense of hearing in Corixa. His -results are thus summarized by Sir John Lubbock[28]: ‘He placed some -Water Boatmen (Corixa) in a deep jar full of water, at the bottom -of which was a layer of mud. He dropped a stone on the mud, but the -insects, which were reposing quietly on some weeds, took no notice. He -then put a piece of glass on the mud, and dropped the stone on to it, -thus making a noise, though the disturbance of the water was the same. -The Water Boatmen, however, at once took to flight.’ - - - - - CHAPTER IV - - SPIDERS, MITES, AND MYRIAPODS - - -In this chapter we shall take examples from two Classes--the -Arachnoi´dea and the Myriap´oda. To the first-named Class belong also -the Scorpions, which, with the Book Scorpions, the Harvestmen, and some -others, may be neglected here. This will leave us only the Spiders and -Mites to deal with. - -Every one knows a Spider when he sees one, though not every one can -give offhand a definition that shall include the whole Order. Let us -endeavour to express their characters in simple terms, keeping in mind -the definition of head, thorax, and abdomen in Chapter II. In Spiders -the head and thorax are joined together in one unsegmented portion, -called the cephalothorax, and this is connected with the abdomen, which -is also unsegmented, by a more or less slender stalk or peduncle. So -that while Insects have three regions, Spiders have but two. We may -express the difference thus: - - Insects head, thorax abdomen. - \---v---/[image] - Spider cephalothorax abdomen. - -The cephalothorax bears six pairs of appendages (Fig. 48A). -Taking these in order, there are-- - - 1. A pair of falces (_an_), representing the antennae of - insects. These have a movable claw-like joint at the extremity, - perforated so as to convey into a wound the secretion from the - poison-glands. - - 2. A pair of five-jointed pedipalps (_p_), sometimes called - maxillary palpi, from the fact that the parts whence they spring - correspond to the maxillae of insects (Fig. 21A, - _d_). In the female the last joint terminates in a claw; in - the male this joint is specially modified for sexual purposes - (Fig. 48B). - - 3. Four pairs of walking legs, of which only the coxae - (_c_) are shown in the diagram. The two front legs are - often used as organs of touch. - -Breathing is carried on by chambered air-tubes or lung-sacs, and in all -our British Spiders (with the single exception of the native Trap-door -Spider, which, by the way, does not make a trap-door) there are also -air-tubes resembling those of Insects. The lung-sacs open to the -external air by stigmata (_st_) on the abdomen, while the ordinary -air-tubes open near the spinnerets (_sp_), the organs employed in -the production of the silky threads from which are formed webs, nests, -egg-bags, and ropes. By means of these threads, spiders drop from their -webs to the ground, construct flying bridges from one point to another, -and even in some sort travel through the air. - -Spiders live upon the juices of their prey, which are drawn up into the -stomach by means of a suctorial apparatus at the end of the gullet. -The young, when they leave the egg, resemble their parents in all -respects but size--that is, they undergo no metamorphosis. - -The eyes of spiders are simple, and six or eight in number. These vary -much in size and relative position, and furnish characters of great -importance in classifying species. Those of the Hunting Spiders, which -make no web, but pursue or spring upon their prey, are usually arranged -in three rows; while those which make webs for the capture of prey have -the eyes in a double row. In all cases they are on the front part of -the upper surface of the cephalothorax. - - [Illustration: - - FIG. 48.--_A._ Scheme of under surface of Wolf - Spider (female). _B._ Pedipalp of male (enlarged). For - other references, see text.] - -The Common Garden Spider (_Epei´ra diade´ma_) is a very good -subject, and there can be no difficulty in procuring any number of -specimens. The smallest garden will be sure to yield a plentiful -supply; and even if we have no garden, a very superficial search -among the hedgerows will give us as many as we can possibly want. -Every one knows this spider, and the beautifully regular web which -it makes. First of all, what one may call the outline of the web -is spun--strong threads stretching from point to point, to which -are attached lines radiating from a common centre. This may be -represented diagrammatically by drawing a circle and producing radii -from the centre to the circumference in all directions, or by making a -rectangular figure and drawing lines to the boundaries from the point -where the diagonals intersect. It must not, however, be supposed that -the outline of the web is of a regular form. In this respect the spider -adapts itself to circumstances, and spins a greater or less number of -supporting threads, as may be necessary. - - [Illustration: FIG. 49.--Garden Spider and Web.] - -Then the spiral is made (Fig. 49) from the centre to the circumference. -The first few turns are of the same character as the radial lines; but -all the rest of the short lines forming the spiral, and connecting -the radial lines, are coated with a viscid secretion, which is the -essential part of the snare; for the victims are really limed like -birds on a twig, not entangled in the threads. It is well to test the -character of the different parts of the spiral, not only by touch, -which is convincing enough, but with pocket lens. Our low powers will -not give such results as are shown in Fig. 50, but we shall have no -difficulty in distinguishing the sticky parts from those not coated -with the secretion. - - [Illustration: FIG. 50.--_A_ Adhesive Threads of - Spiral. _B._ Non-adhesive Radial Threads.] - -It may be doubted whether all the Spiders of this genus make the -spiral in the same way, for observers differ in their description of -what they have seen. Some say that a non-adhesive spiral from centre -to circumference is first made, and that the spider then moves ‘in a -closer spiral from the circumference inwards, biting away the former -spiral, replacing it by another, which is viscid and adhesive[29].’ Dr. -Butler, on the other hand, who ‘watched spiders for months together, -petting, feeding, and trying experiments with them every morning,’ -after describing the making of the first and non-adhesive part of the -spiral, says, ‘This line is not carried to the boundary, but at some -distance from the centre a second is commenced, formed of extremely -viscid silk, upon which the gummy secretion is distinctly visible, -with the aid of a lens, in the form of closely approximated globules -of amber-coloured glue. It is said that when the viscid lines are -completed the spider cuts away the unadhesive lines, but this I have -never observed[30].’ My own observations lead me to believe that Dr. -Butler is correct in his description. Though I have often watched, -I have never seen a spider ‘biting’ away any part of its web, nor -would the falces appear to be adapted for such an operation. They are -piercing, not cutting, weapons. - -The spider may be watched at leisure, if put into a bottle of moderate -size, the top of which should be covered with muslin or calico to -prevent escape. Here it is fairly easy to bring the pocket lens into -play, and to distinguish the different parts of the animal. The eyes, -and their arrangement, should be particularly noticed. - - [Illustration: FIG. 51.--Anchorage of Web.] - -Blackwall, in support of the position that in making their webs -spiders are guided by touch rather than sight, says, ‘Various species, -when confined in spacious glass jars placed in situations absolutely -impervious to light, construct nets which do not exhibit the slightest -irregularity of plan or defect of structure[31].’ My specimens have -always been kept in the light, and in small bottles rather than -spacious jars, but I have never seen spiders attempt to make a -geometrical web under such conditions. - -A bottle which for some months served as a prison-house for a Garden -Spider now stands on my writing-table. Its sides are marked by hundreds -of ‘anchorages’--but the threads cross and recross, forming in some -parts a kind of sheet, and in others a tangled mass. Some of these -threads must have been covered with viscid secretion, for flies were -limed, and so fell a prey to the spider. Their dried skins are dotted -about among the threads, and the spider itself perished long ago from -cold. But I keep the bottle as a curiosity, to show that these spiders -do not always make geometrical webs. - -When one has a Garden Spider in a bottle, it may be observed to -practise a curious and very effective method of disabling its prey. -If a bluebottle or any other large fly be dropped and entangled among -the threads, the spider will envelop it in a sheet of web. This is -how Blackwall describes the operation: ‘Causing the victim to rotate -by the action of the third pair of legs and the palps, the first pair -of legs also being frequently employed in a similar manner, they -extend the spinners laterally, and applying to them alternately the -_sustentaculum_ of each posterior leg, they seize and draw out -numerous fine lines in the form of a fillet, which they attach to their -revolving prey, and thus involve it in a dense covering of silk from -one extremity to the other. By means of this stratagem they are capable -of overcoming formidable and powerful insects, such as wasps, bees, and -even large beetles[32].’ - -The operation does not occupy much time; in a very few minutes the fly -is swathed in a silky covering as completely as an Egyptian mummy in -its linen folds. Of course resistance, much less attack, is out of the -question, and when it is thus rendered powerless for harm the spider -proceeds with its meal. - -The _sustentac´ulum_--or support--is a strong movable spine near -the end of the tarsus, on the under side of each of the last pair of -legs. These spines act in opposition to the claws, and thus these -animals are enabled to hold with a firm grasp such lines as they have -occasion to draw from their spinners with the feet of the hind legs, -and such also as they design to attach themselves to. - -With regard to this method of swathing prey, Hudson[33] says of -an Argentine spider, ‘that its intelligence has supplemented this -instinctive procedure with a very curious and unique habit. The -Pholcus, in spite of its size, is a weak creature, possessing -little venom to dispatch its prey with, so that it makes a long and -laborious task of killing a fly. A fly, when caught in a web, is a -noisy creature, and it thus happens that when the Daddy longlegs--as -Anglo-Argentines have dubbed this species--succeeds in snaring a -captive, the shrill outrageous cries of the victim are heard for a -long time--often for ten or twelve minutes. This noise greatly excites -other spiders in the vicinity, and presently they are seen quitting -their webs and hurrying to the scene of conflict. Sometimes the captor -is driven off, and then the strongest or most daring spider carries -away the fly. But where a large colony are allowed to continue for a -long time in undisturbed possession of a ceiling, when one has caught -a fly he proceeds rapidly to throw a covering of web over it, then, -cutting it away, drops it down and lets it hang suspended by a line at -a distance of two or three feet from the ceiling. The other spiders -arrive on the scene, and after a short investigation retreat to their -own webs, and when the coast is clear our spider proceeds to draw up -the captive fly, which is by this time exhausted with its struggles.’ - -In this connexion Hudson notes that spiders are attracted by the sound -of the vibration of a string or wire, thinking it made by an insect -that has been caught; and he says that the stories of tame spiders -are founded on a misunderstanding of the motive that brings the -animal down. We may well doubt if spiders are attracted by music, but -that some spiders possess a sense of hearing, or something analogous -thereto, seems to be proved by the existence of stridulating organs in -certain members of the group. - - [Illustration: FIG. 52.--Foot of Garden Spider.] - - [Illustration: FIG. 53.--Spinnerets of Garden Spider.] - -Two other points remain to be noted. The feet should be examined, -for their structure throws some light on the way in which the Garden -Spider runs so securely to and fro on the radial lines. One of the -legs of a dead specimen should be detached, and its armature of spines -and hairs noted. The foot is armed with three stout claws, which -are pectinated--that is, toothed like a comb, and beneath them are -smaller ones, sometimes described as toothed hairs. It will be easy -to understand what a secure foothold these claws give the animal as it -runs backwards and forwards over the radial lines; for if the web be -shaken by the wind or designedly its owner can take a firm hold with -each foot, and thus have eight separate points of attachment. An inch -hand lens is quite sufficient to give a general idea of the hairy and -spinous clothing of the legs and the position of the claws; but to see -the teeth a higher power--a half-inch--will be necessary. - -It is a good plan to choose a freshly killed specimen for the -examination of its spinnerets. If the spider is laid on its back in a -glass dish, gentle pressure on the abdomen away from the cephalothorax -will cause the material secreted by the spinning-glands to ooze out. -This, however, cannot be done if the specimen has been for some time -in spirit. We shall be able to make out six tubes (four of them larger -than the other two) grouped round the anal aperture; but, for the -present, we must take for granted the fact that these are made up of -a number of smaller tubes, so that the end of each spinneret is not -unlike the rose of a watering-can. A good half-inch will give some -indications of this rose-like appearance. - -The Jumping Spider (_Sal´ticus sce´nicus_) belongs to a family -the members of which make no web or snare for the capture of prey, but -trust for their food-supply to their skill in stalking flies and other -insects, which they capture by a sudden spring. It is from this habit -that the type-genus and the family have received their scientific and -popular names. - -The common British species is extremely abundant, and wherever flies -are plentiful these spiders will not be very far off. This is the case -not only in the country, but also in London and other large towns. It -is a noticeable spider from its coloration--black marked with white. -The eyes are eight in number; though the artist in our illustration -has only represented four. The centre two of the front are the largest -of all, and have been compared not inaptly to bull’s eyes. Two others -are placed on each side of the cephalothorax, so that the eyes form, -roughly, three sides of a square, and the central eyes in the lateral -lines are the smallest. We may represent them thus [image], while the -eyes of the Garden Spider are disposed in this fashion [image]. - - [Illustration: FIG. 54.--Jumping Spider. (Line shows - natural size.)] - - [Illustration: FIG. 55.--Falces of Male Jumping Spider.] - -It requires some little practice to detect the eyes of spiders and to -remember their position in the different genera, but by examining every -spider met with, and consulting some handbook to the group, one will -soon be able to determine the commoner British species. - -With a couple of needles we may remove the falces (Fig. 55) for -examination; and there is no difficulty in mounting them, as shown in -the cut, on a piece of card, so that they may be compared with the same -weapons in other species. For example, the falces of the Garden Spider -differ from those of the Jumping Spider in that they are short and -stout, and the teeth on the basal joint are more in number. - -The following account of the habit of this spider in capturing prey is -from Kirby and Spence’s _Introduction to Entomology_ (ed. 1870, p. -453):--‘When these insects spy a small gnat or fly upon a wall, they -creep very gently towards it with short steps, till they come within a -convenient distance, when they spring upon it suddenly like a tiger. -Bartram observed one of these spiders that jumped two feet upon a -humble-bee. The most amusing account, however, of the motions of these -animals is given by the celebrated Evelyn in his _Travels_. When -at Rome, he often observed a spider of this kind hunting the flies -which alighted upon a rail on which was its station. It kept crawling -under the rail till it arrived at the part opposite to the fly, when -stealing up it would attempt to leap upon it. If it discovered that -it was not perfectly opposite, it would immediately slide down again -unobserved, and at the next attempt would come directly upon the -fly’s back. Did the fly happen not to be within a leap, it would move -towards it so softly, that its motion seemed not more perceptible -than that of the shadow of the gnomon of a dial. If the intended prey -moved, the spider would keep pace with it as exactly as if they were -actuated by one spirit, moving backwards, forwards, or on each side -without turning. When the fly took wing, and pitched itself behind the -huntress, she turned round with the swiftness of thought, and always -kept her head towards it, though to all appearance as immovable as one -of the nails driven into the wood on which was her station: till at -last, being arrived within due distance, swift as lightning she made -the fatal leap and secured her prey.’ - -This spider employs a clever precaution against falling, when about to -spring upon its prey. It applies the end of the abdomen to the surface -on which it stands, and opening its spinnerets, makes an ‘anchorage’ -(Fig. 56). Then, by the act of springing, it draws from the spinnerets -a line attached to the spot from which it started. This line is strong -enough to support the spider in case it misses its prey. - - [Illustration: - - FIG. 56.--_A._ Foot or Jumping Spider. _B._ - Scopula. (Much enlarged.)] - -The foot of the Jumping Spider is extremely interesting, and shows -a very ingenious arrangement, by means of which the animal can run -with difficulty on smooth polished upright surfaces, or retain its -footing when it alights on such surfaces after a spring. We can see -this arrangement in Fig. 56. Just behind the claws is a bundle of -coarse hairs, technically called a _scop´ula_, or little brush. -From these hairs adhesive matter flows, and in this fashion the spider -literally sticks on. With this brush of hairs may be compared the -tarsal cushions of many flies, and the adhesive hairs of Dytiscus -and other beetles (see Chap. II)--though these last have a different -function. - -Diving Spiders (_Argyrone´ta aquat´ica_) are especially suitable -for our purpose. They are very common in most ponds, and in some -places are so abundant as to be almost a nuisance to the collector who -is in search of other things. Three of them are represented in Fig. 57. -One is swimming; another is just entering the bell-shaped web under -water; and the third is just climbing out of the water on to the broad -floating leaves of the water crowfoot. - - [Illustration: FIG. 57.--Diving Spiders.] - -De Geer’s account of these spiders is extremely interesting[34], and -we may verify it for ourselves, for these creatures may be kept without -any trouble. They certainly agree, when a number are kept in captivity, -much better than do other spiders. De Geer kept several in the same -aquarium, and says that when they met they felt each other with their -palps, and opened their falces, but he never saw them do any harm to -each other. I have kept them under similar conditions with the same -result. - -He tells us that these spiders spin under water a cell of strong, -close, white silk, the shape of which he compares to a skull-cap, the -half of a pigeon’s egg, or a diving-bell. In September, 1736, he first -became acquainted with these creatures, and kept one in an aquarium for -four months. It made its cell against the side of the aquarium, and the -top of it rose above the surface of the water. (This was due to its -being inflated. The web was not spun above the surface.) The walls of -the cell were very thin, but it was filled with air, and the spider was -resting inside, head uppermost, with its legs pressed against the body. - -About three months later he found that the mouth of the cell was -closed, and the spider was comfortably settled in its winter quarters. -When pressure was applied the cell burst and the air escaped, mounting -up to the top in bubbles. The spider made its way out, and took an -Asellus that was offered, and made a meal of it. - -De Geer then came to the conclusion that these cells under water were -constructed for the purpose of affording the spider a retreat when the -water was frozen over, so that they could not come to the surface -for a supply of air. He found, however, by observation, that they -were also made in summer by both sexes. In a cell of this kind the -female deposits her eggs--from eighty to a hundred in number, enclosed -in a cocoon of white silk--and keeps guard over them, with her head -defending the entrance to the cell. - -He succeeded in finding out the method by which the Diving Spider fills -its cell with air. He noticed that when the creature was moving about -in the water, its body was covered with a layer of air, and that this -air was renewed from time to time when the animal came to the surface -and raised its abdomen above the water. Loaded, so to speak, with air -in this fashion, the spider descended, and entered the cell backwards, -leaving an air-bubble. Having repeated this several times, at last she -removed all the water from the cell, introducing in its place an equal -quantity of air. - -It is very easy to watch the Diving Spider making its dwelling under -water, and filling it with air. First of all the web is woven in a -bell or thimble shape between the sprays of water-weed, or against the -bottom or side of the aquarium. It is curious to notice how practices -that must be necessary when the creature is at liberty are continued -in captivity where they are useless. A web constructed in running -water, or even in a pond or ditch, is liable to be swept away or to be -emptied of air by a very slight current, so its owner has recourse to -a system of guys and supporting threads, which are not required when -the spider is safely housed in a small aquarium. Nevertheless, the guys -are made. In an eight-ounce bottle I have now a male Diving Spider, -which has lived there for about seven months. Its cell is made between -the whorls of a spray of milfoil, and guy threads have been carried to -no less than five whorls--two above and three below the opening. Now -that it is filled with air, the cell gleams in the water like a great -bubble of quicksilver. The air may be expelled by shaking or tilting -the bottle, and if the web be not damaged the spider will generally -refill it with air, though sometimes it prefers to make a new dwelling. -Fig. 58 shows the cell of a Diving Spider; the white lines represent -supporting threads attached to the water plants. - -In examining dead specimens we shall find that, contrary to what is -usual, the male exceeds the female in size. I have a slide of a male, -with the legs spread out before and behind, and the measurement from -the claws of the first pair of legs to those of the fourth pair is 1¾ -inches. The body is ¾ inch long. The whole surface is more thickly -clothed with hair than is the case with other spiders, and the reason -for this is obvious. This hairy body-covering serves to carry down into -the water a layer of air, and the fringe of hair on the legs makes them -efficient swimming organs. - - [Illustration: FIG. 58.--Cell of Diving Spider.] - -The Order of Mites will yield us subjects for our pocket lens. Mites -are related to Spiders, but form a distinct Order. Like the Spiders, -some are aquatic, though the most of them live on land. Many are -parasitic, during the whole or part of their lives subsisting on -the juices of their hosts: the food of others consists of organic -_débris_, and these seem to be of benefit to man, since they act -as scavengers. If we turn to page 96 we shall there find noted the -points of difference in the arrangement of the main divisions of the -body in Insects and in Spiders. In Mites the distinction between the -cephalothorax and abdomen is lost, and the body is more or less oval or -globular. In the perfect forms there are eight legs; but some, in their -earlier stages, have only six. The mouth may be adapted for biting, -though it is usually suctorial. In the Cheese Mites and some others -breathing seems to be carried on through the skin, for there are no -air-tubes; but in most Mites air-tubes, with two stigmata, are present. - -If we take a dip with the collecting-net in almost any pond we shall -be pretty sure to capture some specimens of Water Mites of the genus -Hydrach´na, easily recognizable by their bright coloration, their eight -swimming legs thickly fringed with hair, and their unceasing activity. -They may be kept in a bottle, or other small vessel, with some -water-weed, and will forage for themselves. In Fig. 59 we shall see -the points we have to look for in examining a Water Mite with a pocket -lens. There should be no difficulty in making out in the specimen all -the details shown in the cut. - -It may be that they will breed: if so we should avail ourselves of -the opportunity of watching their development. Their life-history is -somewhat curious, and is specially interesting from the fact that -while Swammerdam had some faint perception of the true meaning of what -he saw, De Geer, writing a hundred years later, drew entirely wrong -conclusions from similar observations. It was left for Dugès to clear -up the matter in the _Annales des Sciences Naturelles_, 1834. -Before summarizing the account of the French naturalist it may be well -to quote what Swammerdam and De Geer have said on the subject:-- - -‘There is nothing more remarkable in this insect [the Water Scorpion] -than that it constantly appears covered with a prodigious number of -nits of different sorts and sizes, though perhaps we may with more -reason consider them as so many little creatures, which live and grow -by sucking the Scorpion’s blood. These are somewhat of an oblong -figure, approaching to round, and have a shining, and as it were -bloated, surface, without any of the rings observable in most insects. -The neck is oblong and shaped like a pear, with the small end sticking -in the Scorpion’s body. The colour of this insect is a mean between -that of vermilion and purple; and when it is pretty well grown there -appears within it an elegant transparent spot or particle (Fig. 59). - - [Illustration: FIG. 59.--Red Water Mite (nat. size, and - under surface magnified).] - -‘This spot or particle induced me to consider with more attention -this minute and hitherto unregarded insect, and even to undertake the -dissection of it. But who would imagine that on this examination it -should prove a perfect and surprising insect? This is, however, a -certain fact; and thus in that infinite variety of works, by means of -which God is pleased to make Himself known to us, we ever meet with new -matter of admiration and astonishment. - -‘This little creature being extracted from the shell that covered it, -looks like a young spider before it has left its egg. On the fore part -is the head (Fig. 43D, _a_) and on its head are the eyes, _b_: under -the eyes are placed its little legs elegantly coiled and folded, _c_ -_c_; but they appear much more distinctly on turning the insect on its -back, _d_ _d_; and in this situation also it best appears with what art -these legs are laid up in the shell, and all are covered with hair. -The colour of this little creature is, as I have already observed, a -mean between that of vermilion and purple; and this colour shows itself -through the coat or shell, which is transparent. I cannot determine to -what species of insects this is to be referred; nor can I say to what -size it grows, or by what kind of creature it is thus deposited on the -Water Scorpion in the form of an egg, there to receive life and growth. -Nevertheless, I cannot but look on the discovery I have made as very -interesting, since it proves that there are in the nature of things -eggs which acquire a sensible growth by an entraneous nourishment, -unless perhaps some naturalist should choose to consider this as a -complete insect, rather than as an egg; nor shall I strenuously oppose -his opinion, seeing that, in all cases, the egg is in reality no -other than the insect itself, which remains in that state till it has -acquired sufficient strength to break its prison, and live without such -a covering[35].’ - -Having quoted Swammerdam, let us see what De Geer has to say on the -subject:-- - -‘On the body and legs of many aquatic insects, such as Dytiscus and -Water Scorpions, may be frequently seen little oval, seed-like bodies, -of a bright red colour, firmly attached, and, as it were, implanted -in the skin, by a little stalk. I have had Water Scorpions with the -upper surface so covered with these red bodies that there was scarcely -a vacant space on the skin. They are most frequently to be seen in -the spring; but the insects on which there was such a great number -did not live long with me. Having crushed some of these seed-like -bodies, I found them filled with red liquid matter. I am convinced, by -experiment, that they are the eggs of Water Mites, since there came out -of them little red Mites with round bodies and long legs, which swam -about with great swiftness. - -‘These red Water Mites, then, attach their eggs to the bodies and legs -of larger aquatic insects, and there they remain till the young are -hatched. And since we find eggs of many different sizes, we may be -sure that they grow and increase in size, doubtless owing to a certain -nutritive juice which passes from the body of the insect into the egg. -Hence it is, as I have seen myself, that Water Scorpions loaded with -these eggs become weak and feeble, because they are obliged to furnish -their hangers-on with nourishment from their own bodies. Moreover, -these eggs appear to cause the Water Scorpions some irritation or -uneasiness, since I have often seen them rub with their feet those -parts of the body where the eggs were; and perhaps they did this with -the view of rubbing them off, but they were too securely fastened[36].’ - -Dugès watched the development of the common Red Water Mite (Fig. 59), -and tells us that towards the end of May the females deposit their eggs -in the leaves of pondweed, which they puncture with their beaks. The -larva (Fig. 60), red in colour, with six legs, is free-swimming, and -has a large beak, which looks like a great head, and terminates in a -narrow mouth. It is not known how long this larval stage continues; -but in the next stage (Fig. 61) the Mite becomes parasitic on aquatic -beetles and bugs, fastening its beak into the body of its host, -from which it derives its nourishment. The legs and palps are often -retracted or absorbed, so that it is not difficult to understand -how it was Swammerdam and De Geer took these parasitic nymphs to -be the eggs of the Mite. During their parasitic condition they -increase considerably in size, at last emerging as adult eight-legged -free-swimming Mites. It was just before the emergence of the Mite -that Swammerdam examined the parasitic nymph, for he figures the -‘insect,’ which he extracted from the egg, as having eight legs (Fig. -43D). - - [Illustration: FIG. 60.--Larva of Water Mite.] - - [Illustration: FIG. 61.--Nymph of Water Mite.] - -I once found a Water Mite in the body of a Dytiscus[37]. I was -breaking up the beetle, and had removed the elytra and the wings. I -only wanted the external skeleton; so a slit was made between the -plates of the dorsal and ventral surface, and the intestines removed. -The Mite was embedded in the fat-body. I could find no mention in the -literature of Beetles or Mites of any similar occurrence; and should -scarcely have mentioned it here, had I not been unexpectedly confirmed -by my friend Mr. G. E. Mainland, F.R.M.S., who once had a similar -experience, and who kindly allows me to quote from a letter he sent me -on the subject:-- - -‘I am sorry to say I can find no documentary evidence as to the -Arachnid I found embedded in the tissues of Dytiscus, but a good deal -has come back to my recollection. On removing the right elytron and -slitting up the dorsal surface, I found it in the tissue close up to -the thorax. I cannot recollect what ultimately became of it, after I -had shown it to friends at the Hackney Microscopical Society.... I know -that I carefully measured the Hydrachna (which was abnormally large) -and its relative size to that of its host, and made a comparison in a -lecture (to the Senior Band of Hope at St. Michael’s, Hackney) of a man -with a creature as large as a guinea-pig under his shoulder-blade.’ - -The occurrence of the Mite _inside_ the Beetle was, of course, -quite exceptional. It probably found its way in through one of the -abdominal spiracles. - -The Beetle Mite (_Gam´asus coleoptrato´rum_) (Fig. 62) is -extremely common, and is parasitic on the Dung Beetle and on the Humble -Bee, so that in order to examine the parasite we must capture the host. -There can be no difficulty about this, for Dung Beetles and Humble Bees -are plentiful enough. This Beetle Mite, apparently, does not infest -other species of beetles. I have kept the Devil’s Coach Horse in a -bottle with the common Dung Beetle for some months, and though the -latter swarmed with these parasites, they never left their host for -the other beetle. Even when removed by means of a small brush from one -beetle to the other, they left the Devil’s Coach Horse of their own -accord, and soon made their way back to the Dung Beetle. - - [Illustration: FIG. 62.--Beetle Mite.] - -These parasites, with their host, came into my possession in a strange -way. A friend, who knew my hobbies, told me that he had managed to -procure for me some young beetles just born. I ventured to suggest that -beetles were not born as beetles, but in quite a different shape. My -suggestion was received unsympathetically, and I was told that I should -alter my opinion when the creatures were sent me. But I did not. The -box contained a Dung Beetle, over which were swarming scores of these -little Mites, and I had some difficulty in convincing the gentleman -who sent them to me that these Mites were not the young of the beetle. - -We should compare this Beetle Mite with the Water Mite, and notice the -difference in the mouth parts and the legs, which have a large pad -between the claws. - -We may find another Beetle Mite, closely allied to this species, on the -Devil’s Coach Horse, and some of its near relations. This Mite was also -known to De Geer[38], whose remarks upon it are worth quoting, in a -condensed form. - -He found a beetle covered with these Mites, and on examining them with -a hand lens saw that they were attached to their host by a long thread -or stalk, which came from the posterior end of the body. Several Mites, -he tells us, were joined together by one thread which fastened them all -to the beetle; and he came to the conclusion that the parasites were -nourished at the expense of the beetle, the thread serving to convey -the juices of its body to them. - -‘It is very singular,’ he says, ‘to see living insects planted on the -body of larger insects, from which they draw their subsistence by means -of a thread or stalk.’ And then he goes on to compare these ‘vegetative -Mites,’ as he calls them, with the ‘eggs’ of the Water Mites, which -he found on Dytiscus and the Water Scorpion. The thread exists, and -the Mites are attached by it to their host, but they do not draw -nourishment through it from the beetle, for it is composed of their -excrements. - -The Myriapods are worm-shaped creatures, breathing by means of -air-tubes, and furnished with a number of limbs closely resembling -each other. There are two groups: the Centipedes and the Millepedes. -The former have the body flattened, with one pair of appendages to each -segment, the first pair being modified into piercing poison-organs, and -they feed on living prey. The body of the Millepedes is round, with two -pairs of appendages to each segment; they have no poison-organs, and -their food consists chiefly, if not entirely, of vegetable matter. - -There seems to be some doubt, however, as to whether _Ju´lus_, one -of the commonest Millepedes, does not occasionally indulge in animal -food. In _Nature Notes_ (Jan. 1896) there was a review of the -_Cambridge Natural History_ (vol. v). The reviewer, in a brief -summary of Mr. Sinclair’s part of the book (the Myriapods), said, -after describing the Centipedes: ‘The millepedes, on the contrary, are -sluggish vegetarians, with hard, cylindrical bodies, &c.’ On this a -correspondent wrote in the March number: ‘Some time ago my attention -was attracted to a large earthworm, writhing and twisting about on -the garden path, as though in pain, or through having received some -injury. On examining it more closely to ascertain the cause of its -unusual movements, I found that a millepede had fastened itself to the -side of the worm, and appeared to be boring or eating its way into -the body, whilst the most violent efforts on the part of the worm -were ineffectual in shaking off its antagonist. If the millepede is -a vegetarian, what could be its object in attacking so harmless and -defenceless a creature as the earthworm? The above, which I take to -be a millepede, is the black or dark-coloured creature “with hard, -cylindrical body” ordinarily found coiled up in a spiral under stones -or rubbish.’ - -The editor, as a matter of course, referred the matter to the writer -of the review. His reply was as follows: ‘If there is no mistake -about the identity of the aggressor in the account cited above, the -observation is one of considerable interest; for, so far as we are -aware, it is the only case on record of a millepede being guilty -of such conduct. But were it not for the positive statement that -the species was the dark-coloured creature with a hard, cylindrical -body, which is ordinarily found coiled up in a spiral under stones -or rubbish--a description which exactly applies to the millepedes of -the genus _Julus_--we should have concluded without hesitation -that the struggle in question was merely one of those that habitually -takes place between the centipedes of the genera _Litho´bius_ or -_Geoph´ilus_ and the earthworms upon which they feed.’ - -Both the Centipedes and Millepedes are shy, light-shunning animals, -and if we turn over some stones in the garden or in a walk through the -fields we shall probably find specimens enough to serve us in getting -some idea of both groups. - -The Centipedes are sometimes called ‘Hundred-legs,’ but this implies -the possession of many more legs than the creatures really have. In -Norfolk and Suffolk the people call them ‘Forty-legs,’ and this is much -nearer the mark. - -_Litho´bius forfica´tus_, about an inch long and rufous brown in -colour, is extremely abundant under stones and the bark of trees, and -in cellars and outhouses. These animals run with great rapidity when -disturbed, so that one needs to be on the alert to seize them when -they are driven from the places in which they lurk. The body has nine -principal and six subsidiary or smaller rings, and there are fifteen -pairs of walking legs, besides the first pair, which are modified to -serve as poison-organs. De Geer says that he never dared to pick up -these Centipedes with ungloved hands, because he had seen a fly, which -had been bitten by one, die on the spot, ‘which seems to be a sign that -their bite is venomous.’ He examined their modified legs with a good -microscope, but could not distinguish any opening. There is, however, -an opening, as De Geer suspected, though he could not distinguish it; -it lies near the point, and we may also trace the canal through the -claw down to the poison-glands which lie, one on each side, at the base -of the claws. The mouth parts resemble those of insects, and may be -dissected out in the same way. When this Centipede walks, says De Geer, -it does not use the last four pairs of legs, but drags them after it; -but when it walks backwards, which it does as well as forwards, it then -makes use of these four pairs of legs in the same way as the others. If -we keep Lithobius alive we shall see that it can walk backwards, though -it can scarcely be said to go as well one way as the other. From the -same old writer some useful hints as to the method of keeping these -animals may be gathered. Those that he kept in a vessel without any -moisture soon died, and were quite dried up in twenty-four hours, which -will teach us to keep them in a vessel with damp earth, shaded from -light and heat. - -Dr. Sharp[39] gives some interesting details about the breeding habits -of Lithobius, and describes, for the first time, the uses of the two -hooks on the under surface of the body of the female. - -He experimented with Centipedes and Millepedes. Keeping them in large -shallow glass vessels, the bottom of which was covered with a layer -of earth, he fed the specimens of Lithobius on insects and worms, and -sometimes on raw chopped meat, but they did not thrive on this as they -did on prey which they could kill for themselves. - - [Illustration: FIG. 63.--_A._ _Lithobius - forficatus._ _B._ Mouth parts seen from below (After - Graber.)] - -Lithobius, he tells us, lays but few eggs compared with the number -deposited by Julus. Each egg, as it leaves the oviduct, is received -by the hooks mentioned above, and by means of them it is rolled on -the soil till a covering of earth adheres to the viscous material -with which the egg is coated. The male considers the eggs special -delicacies, and devours them whenever he has the opportunity. It is to -prevent this that the female covers them with earth, so that the male -may not recognize them. - -Geophilus is a much longer animal than Lithobius, for its body may -consist of from 80 to 180 rings. The species have no eyes. Several of -them are common, especially in the south of England, and possess, as -do many genera of the same family, the property of phosphorescence, -whence have arisen the stories of ‘luminous earthworms’ current from -time to time. _Geophilus crassipes_ is the form most frequently -captured when displaying its light. It is from one inch to two inches -long, of a reddish-orange colour, and somewhat worm-like in shape. Mr. -Pocock, of the British Museum (Natural History), says: ‘The property -of luminosity lies in an adhesive fluid secreted by glands which open -upon the lower surface of the body, and the power of discharging or -retaining the fluid appears to be entirely under the centipede’s -control. The phenomenon is observable during the autumn months, from -about the middle of September to the end of November, and although its -significance is not clearly understood, it is generally believed to be -connected with the pairing of the sexes[40].’ - -During a visit to the seaside it is well to look out for specimens of -a marine Centipede, which is, apparently, not very common. It is said -to occur ‘under stones and sea-weeds on the shore at or near Plymouth’; -and in 1895 I had the good fortune to meet with one at Bexhill. -This Centipede does not live in the sea, but will survive prolonged -immersion in salt water. It is far too valuable for us to pick to -pieces, so that, if we should have the good fortune to meet with one, -we should carefully examine it, making what notes are necessary, and -then pickle the specimen and send it to the British Museum, Cromwell -Road, S.W. The tube should be labelled with the place and date of -capture, and it should be stated on the label whether the animal was -taken above or below high-water mark. - -The Common Millepede--often miscalled the wireworm--is readily -distinguished by the absence of poison-claws, and its cylindrical -worm-like appearance. De Geer, who of course adopted the Linnaean -definition of ‘Insects,’ says of the Millepedes of the genus Julus, to -which our Common Millepede (_Ju´lus terres´tris_) belongs: ‘They -form, as it were, the last link of the chain which unites the class of -Insects to that of Worms, for the body is elongated and cylindrical; -and though they have a great number of feet, these are so short, that -when these animals walk, they seem rather to glide along after the -fashion of legless worms[41].’ - - [Illustration: FIG. 64.--The Common Millepede.] - -Dr. Sharp says that these animals do very well in confinement, and he -found that sliced apples and grass formed the best food for them. He -watched the process of nest-making and egg-laying, and these creatures -are so abundant, and the necessary appliances so simple, that we may -follow his example and see it for ourselves. His arrangements were the -same as for Lithobius, and he saw the female make a hollow sphere of a -bit of earth, stuck together by the secretion from the salivary glands, -and smooth on the inside. A small hole was left on the top, and through -this she passed in from 60 to 100 eggs, closing the aperture with earth -moistened with the salivary secretion. The eggs were hatched in about -twelve days. The young of all the Myriapods when they leave the egg -have but three pairs of legs, but the number of limbs and segments is -increased at each successive moult. - -Having watched our Millepedes in confinement, it will be well to take a -preserved specimen and examine it carefully with the pocket lens, so as -to compare it with the Centipede; then to compare both with the common -earthworm, and to note the points of likeness and of difference. The -dark spots on each segment in the illustration show the stigmata. - - [Illustration: FIG. 65.--Segments of Millepede - (magnified).] - - - - - CHAPTER V - - CRUSTACEANS.--PRAWN, SHRIMP, MYSIS, CRABS; - AMPHIPODS; ISOPODS - - -The next group of Arthropod animals with which we have to deal is that -of the Crusta´cea. Some or other of the members of this class are -well known to everybody, if only in the shape of toothsome food--the -Prawn, the Shrimp, the Lobster, the Crayfish, and the Crab. The great -characteristic of this class of the Arthropod phylum is the so-called -‘shell,’ which differs greatly from true shell in being composed of -chitine, hardened with salts of lime. Most of the species live in the -water and breathe by means of gills or through the skin. In dealing -with these creatures, some long words must be employed, if our present -work on them is to be a stepping-stone to something more advanced. The -difficulty is more apparent than real, and if boldly faced will soon be -overcome. - -Our first division, or sub-class, of the Crusta´cea is that of the -Malacos´traca, or animals with soft shells--a name originally adopted, -as Mr. Stebbing tells us[42], ‘to distinguish such creatures as crabs -and crawfish and prawns from such others as oysters and clams; not -because of the absolute, but because of the comparative softness -of their shells.’ Under this sub-class are grouped two Orders--the -Stalked-eyed and the Sessile-eyed Crustaceans, the technical names for -which are the Podophthal´ma and the Edriophthal´ma. - -To the Stalked-eyed Crustaceans belong the Prawn, the Shrimp, Mysis, -or the Opossum Shrimp, and the Crabs, to mention only those forms with -which we are dealing here. The reason for scientific and popular names -will be evident if living or spirit specimens are examined, for it will -be seen that the eyes are elevated on stalks. Mr. Stebbing[43] relates -an amusing story of a very intelligent student, who, on being told that -the eyes (of the shrimp) were stalked, candidly confessed to having -always thought that this appearance was due to their having been forced -out of the head by boiling. - -The general shape of a Prawn (_Palaemon serratus_) is fairly familiar -to everybody. The body is divided into two principal regions--the -carapace, or cephalothorax, as it used to be called (formed by the -union of the head and thorax), and the pleon, or swimming part. The -carapace has a projecting beak or rostrum, and is unsegmented; the -pleon is divided into segments, and the whole may be represented thus:-- - - ---- -- -- -- -- -- -- ) - _c_ 1 2 3 4 5 6 _t_ - -where the long stroke (_c_) stands for the carapace, the shorter ones -(1–6) for the segments of the pleon, and the ) for the telson or tail. -The carapace consists of fourteen united segments, and this will give -twenty or twenty-one segments in all, according as we reckon the telson -an appendage of the sixth segment of the abdomen, or as a distinct -segment. The carapace bears the eyes, two pairs of antennae, six pairs -of mouth appendages, and five pairs of walking legs or perei´opods, -normally with seven joints--in all, fourteen pairs of appendages, that -is, one pair for each of the fourteen segments of which the carapace -is composed. The segments 1–5 of the ple´on bear swimming feet, or -ple´opods, and the female uses these for retaining the eggs, which she -bears about with her. In this fashion the ‘hen’ lobster carries her -‘berries.’ - -The Prawn is a capital inmate of the aquarium, and as it does well -in confinement, specimens should be kept in order to get a general -acquaintance with their form and external anatomy, and to watch their -habits. The Common Prawn will answer the purpose, but still better is -_Palaemone´tes varians_, an exceedingly common species. It has -this advantage, that it ‘seems to be equally at home in salt water -and fresh.’ The only condition necessary is a good supply of food, -and this may be furnished by putting into the aquarium from time to -time a quantity of water-fleas. If these Prawns are well fed they will -shed their skins at frequent intervals, and this operation will give -us material for examination, for the cast skin will serve our purpose -almost as well as a spirit specimen. - -Some of these Prawns are now living in one of my aquaria. They were -taken in a brackish dyke or cut near Newhaven, in Sussex, and in -the mud which was brought back with them were a number of small -bivalves of the genus _Sphaerium_. Most people know Mr. Kew’s -exceedingly interesting book, _The Dispersal of Shells_[44]. -In it he relates some extraordinary instances of the way in which -species of shells are carried short distances, and may be carried -from one district or country to another. These Prawns offered a good -illustration of this, and practically confirmed some of the statements -in his book, for on several occasions they were seen with the bivalve -shells attached to their walking legs. The molluscs lay half buried -in the mud and vegetable _débris_ at the bottom of the tank, -and as the Prawns walked about they sometimes trod between the open -valves, which, as they closed, fastened on to the intruding limb. On -one occasion the molluscs did not relax their grasp for days; and had -this incident occurred when the creatures were at liberty the molluscs -might have been carried for a considerable distance. If specimens of -_Sphaerium_ are put into an aquarium containing Prawns of this -kind, it is probable that before very long the crustaceans will have -one or two attached to some of their limbs. - -Prawns are exceedingly beautiful, and if we get hold of live specimens, -from salt water or fresh, they should be put into an aquarium--the -smaller, in reason, the better--so that their motions may be watched -with the hand lens. If much weed be put in, the Prawns will use their -walking legs in preference, while if there is little vegetation the -powerful tail-fan will be employed for motion backwards, while the five -pairs of limbs on the abdomen enable their owners to move forwards -through the water. - -From Fig. 66 one may get a good notion of a Prawn, and of the points -in which Prawns, in the zoological sense of the word, differ from -Shrimps. The head of the Prawn is armed in front with a long blade-like -beak, studded along its upper and lower edges with a series of teeth -like those of a saw, and the second leg is chelate, that is, armed with -pincers, resembling, in miniature, that of a lobster or crab. In the -Shrimp, on the contrary, there is scarcely a trace of the beak, and -the first leg is incompletely chelate, or sub-chelate[45] (Fig. 67), -its last joint folding back upon the one that supports it, just as the -blade of a pocket-knife closes on its handle. These two distinctions -hold good between all Prawns and all true Shrimps. - - [Illustration: FIG. 66.--Prawn.] - -Now let us go over our Prawn--a spirit specimen--in detail. The -antennae may be separated, and examined, and the appendages of the -inner pair distinguished, for at first it may be thought that there -are more than two pairs. This, however, is not the case, as should be -ascertained by actual investigation. A needle inserted at the base of -the outer antennae will separate the first three segments, bearing -respectively the eyes, and the first and second pairs of antennae. -The eye should be carefully looked at to make out that it is really -compound. Then the joints of the antennae, each with its circle of -sense-hairs, are to be noticed. Last of all, the inner pair of antennae -deserve attention, for these carry in the basal joint an organ of -hearing. This joint is large and sac-like, and contains an opening -through which grains of sand are introduced by the animal itself. The -grains serve to transmit the vibrations of the water in the sac to the -auditory hairs, to each of which a branch is sent off from the auditory -nerve. If the joint is opened the sand will be found. The first -antennae of a lobster or crayfish may also be examined and compared. - -The mouth organs, of which there are six pairs, will offer some -difficulty, and for this reason it may be well to pass them over in -this case and to deal with these organs generally when treating of the -Crab. - -Beneath the outer foot-jaws are the first pair of walking feet, which -are used as cleansing organs. Gosse describes them as ‘beset with hairs -which stand out at right angles to the length of the limb, radiating in -all directions like the bristles of a bottle-brush.’ If we watch our -Prawn in life, we shall frequently see these limbs in active operation. -They are brought to bear on every part of the body within reach. -Sowerby says[46]: ‘The prawn loves to be clean, and he takes surprising -pains to keep himself so. Drawing up his tail and abdomen, he subjects -their under surface to the most careful revision, scrubbing and poking -between the lappets of the shell and body, diving into every crevice, -and with the pincer-hand picking out every speck too large to brush -away.’ The next pair of legs are also chelate; but the three following -pairs are armed with claws, and it is upon the points of these that the -animal walks on the bottom. The pincers of the second pair of legs are -used to pick up food and bring it up to the mouth organs, where it is -taken by the outer foot-jaws, and passed into the mouth. The swimming -feet carry two branches, finely fringed with hairs. - - [Illustration: FIG. 67. First walking leg of Shrimp - (enlarged).] - -If the carapace be removed the gills at the base of the walking feet -will be exposed. These consist of thin leaf-like plates attached to a -central stalk, and they are aërated by water passing in behind and out -in front. - -After what has been said of the Prawn, little space need be devoted -to the Shrimp, for it may be gone over in precisely the same way. It -will be sufficient to call attention to the difference in the antennae, -to the rudimentary rostrum or beak, and to emphasize the distinction -between the terminal joints of the first leg in the two creatures. The -leg shown in Fig. 67 corresponds to the limb used for cleansing by the -Prawn. - -There is a great difference in their habits, for Shrimps burrow in the -sand for concealment. In doing this the swimming feet, as well as the -walking legs, are brought into action, and when the Shrimp is settling -down, sand is swept over its back by the antennae, to render the -concealment complete. - -In many of the rock-pools round the coast, and also in brackish water, -Mysis, or the Opossum Shrimp, may be met with. It is not, so far as my -experience goes, a good inmate of the aquarium, but it is extremely -interesting from the fact that, unlike its higher relations, the -auditory apparatus is not situated in the antennae, but in the plates -of the telson (Fig. 68E). - - [Illustration: FIG. 68.--Mysis, or the Opossum Shrimp.] - -Mysis is shrimp-like in general appearance but differs from Shrimps -in the structure of the legs, in the absence of gills, and in other -particulars. - -The telson consists of five pieces. In each of the two inner and -smaller pieces is an oval sac, like that described in the basal joints -of the first antennae of the Prawn, containing a single lens-shaped -otolith, consisting of chalky matter embedded in some organic substance. - -‘The vibration of the hairs [in this sac] is mechanical, not depending -on the life of the animal. Hensen took a Mysis, and fixed it in such -a position that he could watch particular hairs with a microscope. He -then sounded a scale; to most of the notes the hairs remained entirely -passive, but to some one it responded so violently and vibrated so -rapidly as to become invisible. When the note ceased the hair became -quiet; as soon as it was re-sounded, the hair at once began to vibrate -again. Other hairs, in the same way, responded to other notes. The -relation of the hairs to particular notes is probably determined by -various conditions; for instance, by the length, thickness, &c.[47]’ - -We shall not be able at present to repeat Hensen’s experiment, but we -may break up the sac and extract the otolith, which may be seen with -the lenses at our command. - -Small specimens of the Shore Crab (_Car´cinus mae´nas_) are fair -game for us. They will interest us while living in the aquarium, and -when dead we can put them into pickle, and break them up at our leisure. - -The broad shell of the Crab--the crab-cart of children--corresponds -to the carapace of the Lobster, the Prawn, and the Shrimp, and bears -the same number of appendages--fourteen pairs. To make out the pleon -or swimming part, it is only necessary to lay the crab on its back, -and, with a needle, or small knife, turn back the flap--or ‘apron,’ -as fishermen call it--which lies in a groove on the under surface. -Here we shall find the pleopods, or swimming feet, though they are not -really used for that purpose. The eyes, the two pairs of antennae, -and the five pairs of walking legs will offer no difficulty. It is -only necessary to remark that the terminal joints of the last pair of -walking legs are flattened and fringed with hair, showing some approach -to the swimming crabs, which use those organs to swim with. - -Now we may examine the mouth organs, of which there are six pairs. -To do this, the crab may be fixed, with the back downwards, or held -lightly but firmly in the left hand. The latter plan is perhaps the -more convenient. The index and middle fingers should support the -carapace, and the thumb should be placed on the pleon. The outer pair -of mouth organs are the third maxillipedes, or jaw-feet. These close -the area of the mouth, somewhat after the fashion of the double-doors -of a cupboard, though the hinging, of course, is different. To open -these jaw-feet, a needle should be inserted at the top, with a gentle -pressure downwards and outwards. The back of the crab is turned away -from us, so that the left jaw-foot should be pressed outwards to the -right, and the right jaw-foot to the left. - -Theoretically these limbs consist of the same number of joints as -the perei´opods or walking legs; and this is to be borne in mind, -even if we do not succeed--and we probably shall not--in tracing the -full number of seven joints. But we may notice and count the terminal -joints, and observe the fringing of the limb with hair. - -A similar method of using the needle will enable us to raise the second -and first pairs of maxillipedes, which are of smaller size and softer -structure. - -Having raised these organs, it is well to replace them--to close the -doors, as it were--and then to raise them again, to observe how they -work. They may then be detached and fastened to a small piece of card, -for comparison with similar organs in the lobster and the crayfish, and -with the mouth organs of insects. - -Beneath the maxillipedes are the second and first maxillae--thin, -leaf-like organs. The first-named are furnished with spoon-like scoops, -which serve to carry out from the gill-chamber the water that has -parted with its oxygen in aërating the gills. - -Immediately below the maxillae lie the mandibles, with hard, cutting -edges, by means of which the food is broken up. Each carries a palp. - - [Illustration: FIG. 69.--Maxillipedes and Maxilla - (_b_) of Shore Crab. (_d_) First maxillipede. (After - Savigny.)] - -These inner three pairs should also be detached, and the whole of the -mouth organs arranged on a card thus:-- - - MANDIBLES. - FIRST MAXILLAE. - SECOND MAXILLAE. - FIRST MAXILLIPEDES. - SECOND MAXILLIPEDES. - THIRD MAXILLIPEDES. - -The first attempt will certainly be unsuccessful; and the first few -attempts will probably be unsatisfactory; but we shall gain knowledge -with each successive trial. And knowledge is worth the winning. - -The stomach is interesting, and the gastric mill may be easily -examined. When the mouth organs are removed, there will be no -difficulty in taking out the stomach. This should be cut open with a -needle, and then we shall see the gastric teeth (_g_ _g_) -which grind up the food against the fixed calcareous plate (_b_ -_b_). The lower end of the stomach is set with fine hairs, which -prevent the passage of food into the intestines until it has been -ground fine between these living millstones. A similar arrangement is -found in all the higher Crustacea. The time spent in comparing the -gastric mill of the Crab with the ‘gizzard’ of the Cockroach will not -be thrown away. - -The Broad-clawed Porcelain Crab (_Porcella´na platyche´les_) is -also worth keeping, for it is a droll little creature. These crabs -are generally to be found clinging to the under surface of stones or -of ledges of rocks overhanging small pools. The chief interest of -these crabs, for us, lies in the exceedingly beautiful arrangement for -procuring food with which the outer pair of foot-jaws is furnished. - - [Illustration: - - FIG. 70.--Stomach of Crab laid open. _b_ _b_ - _b_, fixed plate, against which the gastric teeth _g_ - _g_ are opposed; _b´_ _b´_, gastric teeth - enlarged.] - -‘Watching a Broad-claw beneath a stone close to the side of my tank, I -noticed that his long antennae were continually flirted about; these -are doubtless sensitive organs of touch, or some analogous sense, -which inform the animal of the presence, and perhaps of the nature, -of objects within reach. At the same time I remarked that the outer -foot-jaws (pedipalps) were employed alternately in making casts, being -thrown out deliberately, but without intermission, and drawn in, -exactly in the manner of the fringed hand of a Barnacle, of which both -the organ and the action strongly reminded me. I looked at this more -closely with the aid of a lens: each foot-jaw formed a perfect spoon -of hairs, which at every cast expanded and partly closed. That you may -understand this better, I must say that the foot-jaw resembles a sickle -in form, being composed of five joints, of which the last four are -curved like the blade of that implement. Each of these joints is set -along its inner edge with a row of parallel bristles, of which those -of the last joint arch out in a semicircle, continuing the curve of -the limb; the rest of the bristles are curved parallel or concentrical -with these, but diminish in length as they recede downwards. It will be -seen, therefore, that when the joints of the foot-jaw are thrown out, -approaching to a straight line, the curved hairs are made to diverge; -but as the cast is made they resume their parallelism, and sweep in, as -with a net, the atoms of the embraced water[48].’ - -All this description may be verified from a spirit specimen, if the -foot-jaws be carefully removed. And the examination with the lens will -also show that these hairs are plumose, that is, set with smaller hair, -like the barbs of a feather. - -At this point we may conveniently take leave of the Stalk-eyed, and -pass on to the Sessile-eyed, Crustacea. Leaving the Cuma´cea out -of the question, we have two Sub-orders from which to choose our -subjects--the Amphip´oda and the Isop´oda--conveniently Englished, -Am´phipods and I´sopods. We learn from Mr. Stebbing[49] that ‘the -Amphip´oda, which are common in fresh as well as in salt water, were -so named by the French naturalist Latreille, as having feet extending -in all directions, their limbs at the same time having much diversity -of form, in correspondence with diversity of function. The Isop´oda, -or equalfooted animals, besides being found both in fresh and salt -water, have more decidedly than the Amphip´oda extended their range -to the dry land. The name was invented by Latreille in ignorance of -the great number of species, since investigated, in which the feet are -strikingly unlike and unequal. Nevertheless, the name may stand, just -as a rose remains a rose even when it is not rose-coloured.’ These last -two sentences must be borne in mind, for they throw great light on a -subject that may give us some trouble--the question of priority in -nomenclature. - -The majority of the Amphipods live in salt water, but a few are found -in ponds and streams, and some dwell on the shore, near, but not in, -the sea. The animals of this Sub-order are distinctly segmented, and -three regions may be distinguished thus [image], where C stands for -the Cephalon, or head, Per. for the Perei´on, or body, and Pl. for -the Ple´on (literally, the swimming part), or tail. On the head we -shall find two pairs of antennae, the eyes, and the mouth appendages. -Each segment of the perei´on bears a pair of appendages; the first -two pairs are called respectively the first and second gnath´opods -(or jaw-feet), and the other five pairs perei´opods, or walking feet. -The pleon carries three pairs of ple´opods, or swimming feet, on the -first three segments, and each of the following three has a pair of -uropods or tail appendages. It is well to make out these parts in every -specimen that comes in our way. More is learnt by breaking up one -specimen than by reading the clearest description so often that one -knows it by heart. - - [Illustration: FIG. 71.--Gammarus. (After Sars.)] - -We may begin with the Fresh-water Shrimp (_Gam´marus pulex_), -which may be taken abundantly in running water where there is plenty -of vegetation. Willow-moss affords these Crustaceans a favourite -hiding-place. It is an excellent plan to gather a quantity of -weed and shake it over a newspaper or a piece of mackintosh. The -‘Shrimps’--which, by the way, are not really Shrimps--will be dislodged -from the weed, and we shall see them wriggling along on their sides, -from which habit they and their near relatives are often called -‘Scuds,’ and ‘Screws.’ They are useful inmates of an aquarium, because -they feed on decaying animal matter, and so keep the water pure and -sweet. Opinions are divided as to whether these animals feed on -water-plants; it is probable that when their natural food fails them, -they take what comes in their way. I have kept marine and fresh-water -species of Gammarus (the genus to which the Fresh-water Shrimp belongs) -in tanks which contained no other animals, but plenty of vegetation, -and both lived and did well for a considerable time. They are by no -means unwilling to make a meal off the dead body of one of their own -species; but it is exceedingly doubtful if they prey on each other, as -some old writers have asserted. This notion probably arose from the -fact that the male carries the female, which is much smaller, about -with him, during the period of courtship, holding her tightly beneath -his body by means of the fingers of its first two pairs of hands. The -habit is not confined to this genus, nor even to this Sub-order; for -some, if not all, the species of Idotea carry on their courtship in -similar fashion, as does also the Water Woodlouse. For the verification -of statements such as these, a small aquarium is necessary, but the -animals will not be under observation long before the observer will be -convinced of their truth. - -All species of Gammarus, whether living in the sea or fresh water, -may be readily distinguished by the rows of small spines on the three -hinder segments of the pleon, for this is one of the characteristic -marks of the genus. After we have kept specimens in the aquarium for -a time, so as to become familiar with their general appearance and -habits, we will put them to practical use by breaking them up. - -Our first task is to work over the animal as a whole, and to make -out the three regions--ceph´alon, or head; pereī´on, or body; and -plē´on, or swimming part, or tail--into which it is divisible. It -will not be sufficient to do this once, and then to imagine we have -the whole matter fixed in our memory. It should be repeated over and -over again, with every specimen that comes into our hands, till we know -these regions practically, and the number and kind of appendages they -carry. And then the three rows of spines are to be looked for. For all -this the inch lens will be quite sufficient. - -Now let us separate the head. When this is done, and if we use the -lens, we shall at once be able to account for the name ‘Sessile-eyed -Crustacea,’ for the difference between the eyes of our specimen and -those of a shrimp or a crab will be evident. Nor can there be any doubt -that they are compound eyes, though the outer integument is not divided -into facets. The antennae are next to be considered. Of these there -are two pairs, the superior, or inner, pair being the longer. These -antennae consist of three basal joints and a many-jointed flagellum, -or lash, and on each of the inner pair is a secondary appendage, -arising from the distal (or outer) end of the third basal joint. We -may represent one of the superior antennae thus: [image]. The dashes -represent the three basal joints, the long row of dots the many-jointed -flagellum, and the slanting row of dots stands for the secondary -appendage. The sensory-hairs on the joints of the flagellum should be -looked for, and may be made out with the inch lens. The same power will -show the denticle, or tooth-like projection at the base of the lower -antennae. - -Next come the mouth parts. As compared with Crabs, Amphipods seem badly -off in this respect; for the second and third maxillipedes of the -former become the first and second gnathopods of the latter, so that -instead of six pairs of mouth organs the Amphipods have only four. - -It is not an easy matter for a beginner to separate the mouth parts -of an Amphipod, but the difficulty is not insuperable, and will grow -‘small by degrees and beautifully less’ with practice. We have to make -out four pairs of organs arranged in the order given at the side of the -page, the mandibles being the innermost. - - MANDIBLES. - FIRST MAXILLAE. - SECOND MAXILLAE. - MAXILLIPEDES. - -Of course we must begin with the maxillipedes (Fig. 72). The specimen -may be held between the finger and thumb, and the parts picked out with -a needle. It is, however, better and easier to make the dissection -under water. Then we can remove the second and first maxillae, the -latter easily recognizable by its palp or feeler. Last of all come the -mandibles, also bearing a palp. We shall _feel_ these under the -needle, because of their hardened cutting edges. These are distinctly -toothed. When practice has made the separation of these parts fairly -easy, they should be compared with the mouth parts of other members of -the group, so as to utilize the knowledge we have gained. - - [Illustration: FIG. 72.--Maxillipedes of _Gammarus - marinus_ (in centre). _A._ First maxilla. _B._ - Second maxilla (magnified).] - -Next come the two pairs of gnathopods, and in these we have to find -seven joints--which may be denoted by the numbers 1, 2, 3, 4, 5, 6, 7; -1 being the basal joint, or that nearest the body. The sixth joint is -often called the ‘hand,’ and the seventh, the ‘finger.’ The joints vary -greatly in different genera. The walking legs are next to be examined, -and we may notice that the first and second pairs are turned forwards, -and the third, fourth, and fifth pairs backwards. At the bases of these -legs are the breathing apparatus, and the females have leaf-like plates -on the anterior four pairs, forming a pouch in which the eggs are -hatched, and here she shelters her young, and carries them about with -her. - -The following account of this habit is taken from Bate and Westwood’s -_Sessile-eyed Crustaceae_ (i. pp. 380, 381), and was furnished to -the authors of that book by Dr. James Salter: ‘On catching a female -with live larvae, nothing is seen of the progeny till the parent has -become at home in the aquarium, when the little creatures leave her -and swim about in her immediate neighbourhood. The plan I have adopted -to watch this curious habit of maternal protection, has been to place -a single individual in a bottle of sea water. After a time, and that -soon, the little crustacean seems at ease and swims slowly about, -when the young fry leave her and swarm around her in a perfect cloud; -they never leave her for more than half or three-quarters of an inch, -and as she slowly moves about they accompany her. If now one taps the -side of the bottle with one’s finger-nail, the swarm of larvae rush -under their parent, and in a second are out of sight. The parent now -becomes excited, and swims about quickly, as if trying to escape; -but by letting the bottle containing her rest quite still she soon -gets composed, when out come the young larvae again and swim about -as before. This may be repeated as often as the observer wishes, and -always with the same result. I have only seen this in one species, but -it is quite a common species in Poole Harbour, and I have watched the -interesting habit many times.’ - -The swimming legs are, roughly speaking, [image]-shaped--that is, they -consist of a stem, carrying two many-jointed filaments, fringed with -fine plumose hairs. A hair is said to be plumose when it bears smaller -and finer hairs on each side. ‘By folding the tail beneath the body, -and suddenly striking it out again, those animals which exist in the -water, as well as those which live on the shore, are enabled to dart or -leap to a considerable distance[50].’ - - [Illustration: FIG. 73.--Nest-building Amphipod. (From - life.)] - -Our hand lens may be well employed in watching some of the -nest-building Amphipods at work in the aquarium. There can be no -difficulty in keeping these creatures in captivity, and under -observation, as they build their tubes and rear their families. They -are plentiful in every rock pool round the coast, and it would be a -hard matter to dip the net into any such pool without getting a few -specimens. - -They need absolutely no care. The aquarium of the specimen figured -was a four-ounce bottle, tightly corked; and in it was a spray of -Cladophora, on which the animal fed, and the growth of which broke up -the carbon dioxide and set free good store of oxygen. Here it lived for -some months, and built more than one tube for itself against the side -of the bottle. - -It is easy enough through the pocket lens to watch the Amphipod at -work. Like other builders, the first thing it does is to get its -materials ready. Lying on its side, with its back against the glass, -it will rake together with its antennae and jaw-feet a good store of -vegetable _débris_, or if there be no supply of this, will break -off branches from the growing weed. - -But gathering vegetable _débris_, or even filaments of living -weed, is very far from being tube-building. Something more is needed -to bind the mass into a coherent structure. This the animal itself -supplies. The bases of the first two pairs of walking feet are large, -and contain glands which secrete a glutinous cement, that can be spread -like mortar, or spun out into threads. - -An American observer devoted much time to the observation of these -animals. He says[51]: ‘When captured and placed in a small zoophyte -trough, with small branching algae, the individuals almost always -proceeded at once to construct a tube, and could very readily be -observed under the microscope.... The branches were not usually at once -brought near enough together to serve as the framework of the tube, but -were gradually brought together by pulling them in and fastening them -a little at a time until they were brought into the proper position, -where they were firmly held by means of a thick network of fine threads -of cement spun from branch to branch. After the tube had assumed -very nearly its completed form, it was still usually nothing but a -transparent network of cement-threads woven among the branches of the -weed.’ - -Then he describes the method in which the Amphipod works up bits -of weed and its own droppings into the framework of the tube. In -putting its foecal pellets to this use, it reminds one of a species of -Melicerta (_Melicerta janus_)[52], which employs the same material -to coat its gelatinous sheath. - -In breaking up weed and pellets with its foot-jaws and (probably) its -mandibles, the Amphipod recalls the practice of some of the Masking -Crabs, which have been seen to apply to the mouth the material they -were using to deck themselves. Dr. Aurivillius suggests that in the -case of the Crabs there may be an adhesive secretion from the mouth, -as there is possibly in the Amphipods. ‘The spinning was done wholly -with the first and second pereiopods, the tips of which were touched, -from point to point over the inside of the skeleton tube, in a way -that recalled strongly the movements of the hands in playing upon a -piano. The cement adhered at once to the points touched, and spun out -between them in uniform delicate threads. The threads seemed to harden -very quickly after they were spun, and did not seem, even from the -first, to adhere to the animal itself. In one case, in which the entire -construction of the tube was watched, the work was apparently very -nearly or quite completed in little more than half an hour.’ - -The species we are likely to meet with in rock-pools fashion their -tubes in a similar way. The only difference to be noted is that they -employ less cement, and a larger proportion of broken-down weed and -other matters. - -The Sand-hopper (_Tali´trus locus´ta_) and the Shore-hopper -(_Orches´tia littorea_) are so exceedingly plentiful that it may -be well to collect and preserve some during any visit to the seaside. -Both are of fairly large size, and present no great difficulty to us in -making out their several parts. Let us take the Sand-hopper first. - -Sand-hoppers swarm on most sandy shores, where they perform the useful -part of scavengers. They are always found above high-water mark, and -do not enter the sea of their own accord. In hunting for them it is a -good plan to turn over decaying masses of sea-weed, for under them the -Sand-hoppers are sure to swarm. - -Strange tales have been told of their voracity. Bate and Westwood[53] -record the story of a correspondent who says that at Whitsand he ‘saw -“not millions, but cartloads,” of this species lying piled together -along the margin of the sea. They hopped and leaped about, devouring -each other, as if for very wantonness. A handkerchief, which a lady let -fall amongst them, was soon reduced to a piece of open work by the -minute jaws of these small creatures.’ - -This statement has been copied into a good many books, without -criticism. At last Mr. David Robertson tried various experiments with -a view to discover if these creatures would feed on each other, or, -failing other food, put up with cambric or muslin. The specimens upon -which he made his observations did neither the one nor the other. Mr. -Robertson embodied the results of his experiments in a paper which he -read before the Natural History Society of Glasgow[54]. And the story -may be read in an abbreviated form in the Rev. T. R. R. Stebbing’s -_Naturalist of Cumbrae_, p. 329. - -In Gammarus we have a standard with which to compare our Sand-hopper. -The first thing to notice is the difference in the antennae. Here the -superior pair are very short, and carry no secondary appendage, and -the lower pair have no denticle or tooth-like process. There is also -considerable difference in the gnathopods, or jaw-feet, the sixth joint -of which, in the Sand-hopper, does not form a ‘hand.’ The pleopods, or -swimming feet, are small, and are used for leaping. We shall also find -some difference in the details of the mouth parts, especially in the -toothing of the mandibles. - -We now come naturally to the Isop´oda, which are distinguished by the -nearly uniform size of the seven segments which constitute the trunk, -and the seven pairs of limbs borne by these segments. The head is -distinct, and the breathing apparatus is carried on the under side of -the pleon--in these animals not the ‘swimming’ part--five pairs of -plates lying one over another, sometimes covered by a larger outer pair. - -A normal I´sopod may be represented [image:--·······--], where the -small dash will stand for the cephalon, or head; the seven dots for the -segments of the perei´on, and the long dash for the pleon. - -The Common Asellus (_Asellus aquaticus_) of ponds and ditches -is an excellent subject. It lives well in confinement, and if the -conditions are fairly favourable, will increase and multiply. These -animals will forage for themselves, and pick up a comfortable living -from the vegetable _débris_ that always accumulates at the bottom -of an aquarium, and they are not averse from an occasional meal of -animal food. - - [Illustration: FIG. 74. Water Woodlouse.] - -While our specimens of Asellus are moving about in any convenient -vessel, we may verify with the hand lens what has been said about the -general form. Then we may notice the antennae, the inner pair being -much the smaller. There can be no difficulty in discriminating the head -and the eyes; the seven segments of the perei´on, each bearing a pair -of limbs; and the pleon with its two terminal appendages. These last -consist of a stalk bearing two longer filaments, armed with spines, and -ending in a small pencil of hairs. - -It is easy to see that the segments of the pleon have coalesced, so as -to form a continuous plate or shield on the upper surface. - -If we now take our dissecting microscope and place an Asellus in some -water in an excavated 3 in. by 1 in. slip on the stage, examination -with an inch lens will show us a considerable amount of detail. With -the half-inch Leitz lens (see p. 18) one may see quite clearly the -beautifully annulated form of the flagella of the antennae, the sensory -hairs with which these organs are set, and the circulation of the blood -in the limbs and the antennae--the corpuscles moving in a continuous -stream. More than this: we shall be able with the same power to -distinguish tufts of Vorticellids that settle on the Asellus, and the -commensal rotifers that roam about on the body of their host, generally -on the limbs and under surface. - -Now we may turn the Asellus on its back, to examine the breathing -apparatus more closely than we were able to do when the creature was -moving about in the bottle. It will be easy to make out the opercular -plates--modified tail appendages--that open and shut to admit water to, -or allow it to flow out from, the true breathing-plates which function -as gills, and correspond to the swimming feet of the Amphipods. - -In the female there is a pouch beneath the perei´on, in which the eggs -are carried till they are hatched, and which serves as a nursery and -refuge for the young. - -If a good number of these animals be collected they will probably -breed, and then there will be the opportunity of seeing for ourselves -the young carried about in the incubatory pouch. - -There are two other aquatic I´sopods which will make good subjects for -us on account of their great abundance, and the ease with which they -may be kept in any improvised aquarium, with a little weed. They may -both be taken in brackish water, and will live and thrive in fresh -water, without any admixture of salt. Indeed, both have lived for some -months in a small bottle of New River water, in which the only weed is -some willow moss. They feed on this and on the vegetable _débris_ -that accumulates at the bottom of the bottle, and both species have -bred. - -The first is Idot´ea (_I. pelag´ica_), a long, narrow creature, -with very short inner antennae. The last four segments of the pleon -form a plate on the upper surface; and on the under surface the -opercular plates may be opened like tiny folding-doors, to show the -breathing plates. - -These vary greatly in colour. Of another species, Spence, Bate, and -Westwood say: ‘According to our experience the colour of the animal is -dependent upon that of the weed on which it lives. Those that live on -the black fucus are generally very dark purple, while those that we -find on the green algae are brightly verdant; and it has always been -our opinion that this change was due to the food[55].’ - -The other little creature is called Sphaero´ma--it has no English -name--from the fact that it can roll itself into a ball. It is not -difficult to identify, from the fact that all the segments of the pleon -are joined into one plate, the hinder margin of which is entire, thus -[image]. - -The garden will afford us a hunting-ground for the last specimen of -this group for which we have space--the Woodlice. Enough has been said -of the method of looking over and breaking-up I´sopods generally to -render detailed description unnecessary. The inner pair of antennae, -however, are so small as to be readily overlooked: indeed, on first -sight these creatures seem to have but a single pair. Some have, and -others have not, the power of rolling themselves into a ball; and, -concerning the former, Swammerdam tells the following story:-- - -‘One of our maidservants had at one time found a great number of -Woodlice in the garden, contracted into round balls ..., and thinking -she had found a kind of coral beads, she began to put them one after -another on a thread, but it soon happened that these little creatures, -which roll themselves up in such a manner only for fear of harm, and -appear as if they were dead, being obliged to throw off their mask, -resumed their motions. On seeing which, the maidservant was so greatly -astonished, that she threw away the Woodlice and the thread, and cried -out, and ran away[56].’ - - - - - CHAPTER VI - - AQUATIC INSECT LARVAE - - -In this chapter we shall deal with a few aquatic insect larvae. Of -these, some are aquatic also in the perfect condition, while others -emerge from the pupa stage as aërial insects. It requires no great -amount of care to keep these creatures, and some hints on this subject -and on collecting are given in the first chapter. - -The larva of Dytiscus is abundant during the greater part of the year, -and is almost sure to be met with by the collector, who will find it -an extremely interesting object for examination and study. No other -creatures should be put in the same bottle with these larvae; and if -there are several of them in one bottle, it is a good plan to put in -plenty of pondweed, which will often keep them from attacking each -other. - -When full grown, the Dytiscus larva may attain a length of two inches -or rather more. Its colour is dingy brown, and its aspect forbidding -enough to justify the uncomplimentary names that have been bestowed -upon it--Water-devil and Water-tiger. It certainly rivals the tiger in -fierceness, and its method of stealing up to its prey and attacking it -from behind led Swammerdam to call it the Sicarius or Assassin Worm. - -One must not imagine that Swammerdam was ignorant of its nature; ‘worm’ -with him was a general term for any larval form. Indeed, he says, -‘It is extremely probable that some peculiar species of the Water -Beetle proceeds from this worm, when, having remained in the water a -sufficient time, it betakes itself to the land to undergo its mutation; -but this is mere conjecture.’ What was conjecture for him is fact for -us. - -Now let us put our larva into a small tube, and examine it more -closely. The head is large and joined to the first segment of the -thorax by a distinct neck. There are twelve small eyes, six on each -side, a pair of antennae, two pairs of palps, and a large pair of -sickle-shaped mandibles, which Swammerdam calls ‘teeth,’ and says that -‘it is perhaps to contain the muscles such teeth require that Nature -has made the head so large.’ Behind the head come eleven segments, of -which the first and last are the longest. They gradually increase in -width till the sixth, the rest again decreasing, till the eleventh ends -in a blunt point, from which diverge two appendages, thus [image], -thickly fringed on both sides with hair, as are the tenth and eleventh -segments. - -There are six legs, one pair to each of the first three segments. -These also carry fringes of hair, thus increasing their power as -swimming organs; and, in addition, they bear numerous spines, and end -in strong double claws, which must be of service in climbing over -aquatic vegetation, and may assist in holding a struggling victim or in -striking it down, so as to bring it within reach of the mandibles. - -Spiracles will be found--seven on each side. These do not, however, in -the larval condition, serve as breathing organs, though they fulfil -their proper office in the pupa. The air-tubes of the larva open at the -extremity of the last segment. When the larva wants to breathe it comes -to the surface without an effort, for it is lighter than the water it -displaces. The tail rises above the surface, and a fresh supply of air -is taken in. When the larva wishes to descend, a stroke of the tail -sends it downwards, and as it reaches the bottom of the tube it will -cling with its claws to any weed we may have put in with it, or hold on -with them to the glass itself. - -The chief interest of this animal lies in its mandibles, and the method -in which they are employed. It was formerly believed that the mouth of -this larva was closed, so that it could not take solid food, and that -it lived entirely on the juices of its prey, which it sucked up through -its hollow mandibles. - -Swammerdam says of this larva, ‘When about to eat he seizes with the -two teeth (mandibles) the little creatures that come in his way, and -pierces their body with the sharp crooked points. The teeth being -perforated from the points to the roots, he in a surprising manner -sucks through them into his mouth the blood of the unfortunate captive. -This may be easily seen, especially when the blood of his prey is of a -red colour, as the teeth are transparent.’ - -He then describes how he watched one of these larvae feed, and saw the -blood, mixed with air-bubbles, travel up the mandibles. After this he -tells us how, if we have a Dytiscus larva, we may ‘procure ourselves -a very entertaining and surprising sight, by throwing to it a small -earthworm; for let this last move, twine, and otherwise bestir itself -ever so much, the other keeps its hold, and very calmly sucks the blood -of its prisoner.’ - -We may, however, go to work in another fashion. We may dissect out the -mandibles from a dead larva and pass a fine hair into the slit near the -point, and it will come out at the orifice near the base. It is through -this orifice that the nutritive juices of the prey are drawn into the -true mouth. This practical proof that the mandibles are pierced is by -no means so difficult as one might suppose. - -De Geer[57] seems to have been the first to suggest that there must -be some kind of true mouth, and in support of his suggestion tells us -that he saw this larva eating up the solid parts of a Water Woodlouse -(_cloporte_), after having sucked up its juices. More than this, -he places the mouth in what has proved to be the true position, though -he did not solve the mystery as to why it is kept so firmly closed. -This was done by Mr. Burgess, an American naturalist, from whose -paper[58] the following particulars are condensed:-- - -‘Authors have described this creature as mouthless; and if we examine -the slit where we should expect the mouth to be, we find that this slit -ends in a perfectly closed seam. The methods of microscopical research -were brought into play, and a longitudinal section of the head cut and -mounted. This showed that the upper and lower lips were locked together -by a peculiar joint--the upper coming over and locking into the under -lip (Fig. 75).’ - -We may get some idea of this mouth-lock by placing the fingers of the -right hand over those of the left, and then bending them. - -Mr. Burgess concludes his paper thus: ‘We find that the Water-tiger, -far from being mouthless, as ordinarily assumed, has in fact a -very wide mouth, though its lips are closely locked together by a -dove-tailed grooved joint developed for this purpose. Whether this -joint can be unlocked by the animal itself is another question, which -I cannot answer, though De Geer’s observation above quoted makes this -probable. It is, at all events, easy to open the mouth by manipulation -with a pair of forceps.’ - - [Illustration: FIG. 75.--Mouth-lock. _m_, mouth × - 125. (After Burgess.)] - -Professor Miall[59] has verified Burgess’s observations, and carried -them a step further. He found by actual experiment that ‘the mouth-lock -acted automatically, opening when the mandibles opened, and closing -when they closed.’ - -Both these authorities stand very high. Yet, with all respect to them, -it will be well to test these statements before accepting them. - -Something of this mouth-lock may be seen in any well-prepared slide -of a Dytiscus larva. If we hold the slide up to the light and examine -with a power of 10, we shall see a dark line--in some cases two nearly -parallel thinner lines--running from the base of one mandible to the -base of the other. The dark line is the closed mouth-lock. The two -nearly parallel thinner lines are the edges of the lips drawn asunder -in preparing the specimen or by the pressure of the cover-glass. If we -get to see this much, we shall have advanced one step. - - [Illustration: FIG. 76.--Dytiscus Larvae.] - -Next we may verify Professor Miall’s experiment, though not quite in -his way, for such section-cutting as he speaks of is beyond our powers. -Larvae as large as possible should be chosen, and killed by dropping -them into boiling water. The mandibles of one should be allowed to -remain closed, and those of the other plugged open with pith or a small -piece of wood--a bit of a match will serve. By putting each in turn -into an excavated slip with water, carefully covering this with a plain -slip, and holding these slips together with an elastic band, we may -examine the larvae as we did the slide. - -The result will be practically the same. Where the mandibles are -closed, we shall see the dark line; and where they are open, we shall -see the two thinner ones nearly parallel. - -One caution may be necessary. The mandibles bear at the base a -rounded process, which fits into a chitinous cup. It is not difficult -to mistake this for the mouth-lock, with which, however, it is not -connected. - -There is still one other method which we may adopt to see the mouth. -The head of one of these larvae may be cut off, dropped into a strong -solution of caustic potash, where it should remain for a day or two. -After washing it well in water, cut it in half lengthways, and turning -either half upon its side, so as to expose the part cut, examine with -the pocket lens. - -These experiments are by no means difficult. But if carried out step -by step, it will be easy to understand how the larva can suck out the -juices of its prey, and how it can open its mouth to swallow some of -the solid parts. - -The larva does not readily change into a pupa in confinement. If, -however, we wish to rear a beetle, the larva must be plentifully -supplied with food, and removed from a bottle to a flat dish, -where earth can be placed against the side so as to rise above the -water-level. Fig. 77, where a pupa is represented in a bank by the side -of a pond, will give us a hint how to go to work. The time occupied in -pupation will vary according to the temperature of the room--but is -never less than a fortnight. In the open it is probable that the winter -is passed in the pupal condition, the perfect insect emerging in the -spring. Like Land Beetles, it does not assume its dark hue for some -days, but its pale skin darkens by degrees. - - [Illustration: FIG. 77.--Pupa of Dytiscus.] - -The larva of Hydrophilus does not seem to be often taken in this -country. It would make a capital subject for investigation, and the -food-supply could be arranged easily enough. The repetition of the -experiences of Lyonnet, who reared these larvae from the egg, would -be of great interest. He says that he took about thirty larvae from -the brood, and fed them with very small water-snails. These they -devoured in the same way as the larger larvae do. Having seized the -snail with their mandibles, they bent backwards, and supporting it -on their back, which served them for a table, eat it there, without -making any use of their legs to hold their prey. When the supply of -small snails ran short, they did very well with large ones cut up into -pieces, and with tadpoles. If, however, food was not supplied to them, -they fed on each other. But, except when pressed by hunger, they lived -together peaceably enough, and seemed to take pleasure in each other’s -society[60]. - -The larva of _Limnobia replicata_, a Crane-fly allied to, but -smaller than, the well-known Daddy-longlegs, is another excellent -subject for investigation. It is not very often taken; perhaps because -it is not often looked for. But it is common enough, for all that. - -In general appearance these larvae resemble small caterpillars covered -with spines. Some of these are simple and others forked, not much -unlike the letter [image], with a short stem, and the arms slightly -curved. There are no feet, and the last segment carries two pairs of -hooks, one large and the other small. From their position they are -called anal hooks. - -The dykes of the Sussex marshes are an excellent hunting-ground. -Probably the channels of water-meadows, or any other shallow standing -water in which aquatic moss grows, would serve the collector’s purpose -quite as well. And such pieces of water abound all over the country. - -For taking these larvae the ordinary net and bottle are of little use, -though a few may be captured by sweeping backwards and forwards among -patches of aquatic moss. - -There is, however, a far easier and surer method. A good handful of -the moss should be gathered, and put into a shallow vessel half full -of water--a developing-dish answers capitally--and then shaken to and -fro or gently stirred with a small piece of stick. The larvae will curl -into a ring and fall to the bottom, whence they may be picked up and -dropped into a bottle or other receptacle to be taken home. A fair -quantity of moss should be gathered, for this is their favourite food, -and all larvae are greedy feeders. - -Other water-plants, however, do not come amiss to them. Just before -these lines were written I was examining a bottle in which some of -these larvae were kept. It contained a few sprays of willow-moss and -some ivy-leaved duckweed, which floated on the surface. One larva on a -spray of moss was reaching upward, and it was distinctly seen to feed -on the duckweed. This must have been from choice, for there was within -reach plenty of what all observers consider to be its natural food. -This, too, might have been more easily obtained; for, to reach the -duckweed, the larva had to hold on to the moss by the anal hooks, and -extend its body in a fashion analogous to that of the caterpillar of a -geometer moth, which will hold on to a branch with its fore-legs and -claspers and maintain the body at an angle of 45°, sometimes for hours -together. I have also seen them feed on hornwort. - -The larva of this small Crane-fly is not at all difficult to keep. It -is exceedingly hardy, and will survive a great deal of rough treatment. -In November, 1895, I sent three in a tube--securely packed, as I -thought--to a friend in Yorkshire. A few days afterwards I heard, with -regret, ‘that the bottle was broken in transit, and that the larvae -arrived dead.’ Three days later I was gratified by receiving a letter, -from which the following is quoted: ‘The Limnobia larvae have come to -life again. I put them into water as soon as they arrived, and after -lying motionless for many hours they have begun to creep about and -feed.’ - -This is excellent testimony to their powers of endurance, but it is -weak in comparison to that which De Geer supplies[61]. - -He was Marshal of the Court of Sweden, and one November, before leaving -his country house for his official duties at Stockholm, he put four -of these larvae into a vessel of water, and left them to take their -chance. The water froze into a solid mass. When he returned in the -following May he found about half the water thawed, and two of the -larvae dead. The others, though they had been enclosed in ice all the -winter, were lively and in good condition. He put them into another -vessel with fresh water and some aquatic moss, and at once they began -to move about and commenced to feed. Both pupated by the fifteenth of -the month, and the perfect fly emerged after six days in the pupal -stage. - - [Illustration: FIG. 78.--Larva of _Limnobia - replicata_.] - -The following description of this larva is principally condensed from -De Geer, whence the figures are also taken. The body is long and -cylindrical, and divided into eleven segments, of which the first and -largest is sub-triangular. The second and third segments are shorter -than the rest. - -The head (_t_) is very small and completely retractile within -the first segment, the anterior margin of which completely closes -the orifice, so that, in this condition, the creature appears to be -headless. The body is covered with spines, some simple and others -branched. On the first three segments there are only simple spines; -but from the fourth to the tenth segment inclusive there are also on -each segment two forked spines--that is, fourteen in all. On the last -segment the spines are simple, and here are also four chitinous hooks, -one pair much larger than the other. These simple spines carry a white -vessel, which extends throughout their whole length; but in the forked -spines there are two such vessels placed side by side in the stem, and -diverging one to each branch. - -He comes to the conclusion that these spines are probably the breathing -apparatus of the larva, for they are similar to those which he observed -in an aquatic caterpillar. Walker[62] calls these spines ‘long -filamentous processes, which appear to be internally supplied with -air-tubes,’ but he does not seem to have taken the trouble to break up -a specimen, or he would have been in no doubt as to their real nature. -This is shown by the fact that the larva never comes to the surface to -take in a supply of air, but contents itself with the oxygen dissolved -in the water. - - [Illustration: - - FIG. 79.--Forked spine of Limnobia, enlarged; the dark - lines show air-tubes.] - -The pupa is quite as remarkable as the larva, though the breathing -apparatus does not assume the form of spines, but consists of two -‘trumpets,’ one on each side of the head, as is the case with the -pupae of gnats, using that term in a wide sense. The colour is a -greenish-brown, dotted with black. The abdomen is capable of a good -deal of motion from side to side; and by this means the pupa can raise -itself to the surface of the water to take in a supply of air. - -De Geer remarked that when the pupa rose for this purpose it lay with -its body horizontal, having the lips of the trumpets a little above the -surface. It appeared not to like being placed on its back, because in -that position the trumpets cannot be raised above the surface. When he -tried the experiment of putting the pupa back downwards, it wriggled -over by bending the abdomen. - - [Illustration: FIG. 80.--Pupa case of Limnobia. - - (From a photograph taken at the Yorkshire College, Leeds.)] - -On the abdomen there are several chitinous hooks, which serve in some -sort as substitutes for limbs. By their means the pupa can moor itself -to the stems of aquatic plants; and this is necessary, since its -specific gravity being less than that of the water it would be always -at the surface, if it had no such means of anchorage. And of course, -at the top of the water, it would be exposed to the danger of being -snapped up by birds. - -De Geer’s specimen passed six days in the pupal state, and then emerged -as a perfect Crane-fly. My specimens did not emerge till after ten and -eleven days of pupahood, which seems strange, as they were plentifully -supplied with food in their larval stage. - -The fly is a little more than half an inch long, and may be -distinguished from the common Daddy-longlegs by the character of the -wings, which are folded somewhat like those of a wasp, but with this -difference: that the wings of this fly are folded outward, while those -of the wasp are folded inwards. When the insect wishes to fly, it opens -the fold so that the whole wing presents a plane surface, but the fold -reappears directly the Crane-fly ceases its flight (Frontispiece). - - [Illustration: FIG. 81.--Fore-wing of Bee, showing - marginal fold (× 7).] - -De Geer’s allusion to the wing of the wasp might have been extended -to most of the Hymenoptera, as we may see by examining the fore and -hind wings of a bee or a sawfly. Dr. Sharp[63] says, ‘The wings [of -the Hymenoptera] are remarkable for the beautiful manner in which the -hinder one is united to the anterior one, so that the two act in flight -as a single organ. The hind wing is furnished with a series of hooks, -and the hind margin of the front wing is curled over so that the hooks -catch on to it. In some of the parasitic forms the wings ... have no -hooks. The powers of flight, in these cases, are probably but small.’ - -If we were taking our subjects in consecutive order, the larva of -Ptychoptera would properly come here, as being that of a Crane-fly. But -since it will be convenient to examine another larva which resemble -Limnobia in its breathing apparatus, we will take next the larva of -_Parap´onyx stratiota´ta_, one of the China Marks, for it is -extremely interesting and by no means hard to come by. - -The China Marks are small moths, with white wings bearing dark -markings, which have been supposed to resemble Chinese characters. -Their larvae are aquatic in varying degree--that is, some breathe air -in the usual way, by means of spiracles; while others, by means of -gills, breathe the oxygen dissolved in the water. - -Many collectors have, no doubt, taken these larvae, and cast them away -in the belief that they were caddis-worms. Such was the experience of -the Rev. Gregory Bateman, the author of _Fresh-water Aquaria_, -who says (p. 259): ‘While hunting for fresh-water animals, one not -seldom comes across an insect wrapped up in two or more green leaves, -or pieces of leaves, of some aquatic plant. The leaves and the animal -have somewhat the appearance of a caddis-worm in its case; in fact, for -a time, before I knew what it was, I mistook it (and I daresay others -have done so also) for a caddis-worm.’ - -The cases are usually, but not invariably, made from the food-plant -of the insect. Mr. Bateman has noted that these larvae ‘do not -always confine themselves to the same weed, either for food or for -building material.’ This has also been my experience. A larva of the -Brown China Mark, recently taken on the Norfolk Broads--an excellent -collecting ground for aquatic larvae--was put into a tube. The case -had been damaged, and the only vegetation in the tube was a spray of -bladderwort. On examining the tube, after some days, I failed to find -the larva. The reason was evident on removing the cork, a small part -of which had been gnawed away to procure material for the repair of -the larval case, which was affixed to the under side. The larva was -dead and too much decayed to be put into pickle, a circumstance I much -regret, as I should like to have preserved the larva in such a strange -dwelling. As it is, I have only been able to keep the house without its -tenant. - -Pondweed is the usual home of the larva of the Brown China Mark, and -from the leaves of this plant the first larval case is generally -fashioned. This was the species upon which Réaumur made his interesting -observations, most of which have been confirmed by succeeding -observers. In well-grown larvae the contrivance by which the animal -is protected from contact with the water in which it lives should be -noted, as it may be easily, with the hand lens. The skin is thickly set -with tiny protuberances between which the water cannot penetrate, the -surface film stretching from tip to tip of these prominences, just as -it does over the hairs that cover the body of a water-spider. - -De Geer[64] describes an aquatic larva of one of the China Marks -(_Paraponyx stratiotata_), which has its breathing apparatus -fashioned on a similar plan to that of Limnobia, though there is some -difference in the details. He found his specimens on the leaves of the -Water Soldier, and his interesting account recalls the fact to memory -that this remarkable plant was at one time called the Marsh Aloe--an -exceedingly appropriate name. - -He describes the filaments on the body of the larva, and concluded -that they were probably breathing-organs, because of the dark-coloured -vessels within them. These he traced, as we will presently do, to their -union in the stem of the gill, and thence to the air-vessels running -down each side of the body of the larva. He fed them on leaves of the -Water Soldier, and kept them through the winter. In the following June -he found them preparing to undergo their transformation into the pupal -stage, and at the end of the month the moths came out. He was gratified -by seeing the congress of these insects. The females deposited their -eggs on the floating vegetation and on the sides of his aquarium, a -little below the surface of the water, and in about eight days the -young larvae were seen. - - [Illustration: FIG. 82.--Larva of _Paraponyx - stratiotata_ (enlarged).] - -These larvae must be very abundant, though they do not seem to be often -taken by collectors. In describing an allied (American) species, which -is found on Vallisneria and pondweed, Mr. Hart says[65], ‘They feed -at first exposed on the leaf, but later two or even three leaves are -loosely webbed together, face to face, by each larva, between which it -remains concealed while feeding. They are, therefore, hard to discover -unless their hiding-places are broken up by seining, or the like, when -the larvae may be seen swimming about.’ This is, no doubt, the reason -why these larvae are not more often taken. Anything like a seine net is -of course out of the question for us; but masses of vegetation may be -readily broken up by vigorously working the bottle and net backwards -and forwards amongst them. Specimens I have seen were taken among -duckweed; and Mr. Hart mentions one instance of part of the larval case -being constructed of ivy-leaved duckweed, ‘which was abundant there at -that time.’ - -Now let us bring our lens to bear, so that we may make out the external -structure, and recognize the similarity of the breathing-organs of this -Moth-larva to those of the Crane-fly larva already treated of (p. 168). - -In order to make out the scheme of the gills, which is somewhat -complicated, one should first of all distinguish the spiracles, -remembering that they are not functional. And it is best to begin with -those on the middle segments of the body. They may be detected as -little dark spots, sometimes enclosed in a ring. The head, the first -segment of the thorax, and the last segment of the body, bear no gills; -the second segment of the thorax has but two pairs on each side; and -there is but a single gill on each side of the ninth segment of the -body. On the other (nine) body-segments there are the full number -of five gills on each side, arranged two above, and three below the -spiracle. The upper pair are called supra-stigmals, or gills which lie -_above_ the spiracles; the lower pair are called infra-stigmals, -or gills which lie _below_ the spiracles; and the single one, the -lowest, is known as the pedal or foot gill. These technicalities need -not give us any trouble here, in our examination of the larva; nor do -they present any real difficulty. But it is worth while to master the -arrangement as soon as we get hold of one of these larvae, and then we -shall be able to take up and understand technical descriptions of this -aquatic caterpillar and its allies, in so far, at least, as they refer -to the breathing apparatus. - -The gills differ in their character: some few are simple, while most of -them are more or less branched. In Limnobia the branching of the gills -is into a simple fork; in Paraponyx this kind of division also occurs, -and in others most of the gill branches are also given off from the -main stem below one of the branches of the fork. - -In Fig. 84 we have a representation of one of these branched gills. -It will not be difficult for us to make out the details as there -shown. But the vessels that run down into the filaments, constituting -them breathing-organs, are smaller than those of Limnobia, and will -consequently require a little more care and patience before we can -distinguish them. - - [Illustration: - - +---------------+ - | GILL GILL | - | SPIRACLE | - | GILL GILL | - | GILL | - +---------------+ - - FIG. 83.--Diagram of segment of Paraponyx, showing - arrangements of tracheal gills.] - - [Illustration: - - FIG. 84.--Gill of Paraponyx larva. _a_, _b_, - stem; _c_, _d_, _e_, _f_, branches; - _g_, attachment of the air-vessel of the gill to the main - tracheae of the body. (After De Geer.)] - -One would think that, with such an array of gills, this larva ought -to be in good case for its air-supply. It may, perhaps, be doubted -whether this is so. At any rate, the creature adopts the same plan as -the larva of Chironomus, which has no gills at all, for driving away -from its case water that has parted with its oxygen. Water charged with -oxygen pours into the case, and so the air-supply is renewed. This plan -is nothing more than keeping the fore-part of the body in undulating -motion, the tail in both the larvae serving as a point of attachment. -One or two that I have kept made their cases against the side of the -bottle, and so afforded an excellent opportunity of seeing them in this -motion. The Tanypus larva does the same thing. Against the side of one -of my small aquaria a Tanypus larva and a Chironomus larva have both -made tubes; and as I look up from writing these lines I can see them -both hard at this work. - -The larva of the Alder-fly (_Si´alis luta´rius_) is also furnished -with tracheal gills, seven on each side. So little is known of the -life-histories of common insects that it may be profitable to introduce -the account of an observer who watched the deposition of the eggs and -the emergence of the young larvae: - -‘On April 25 I found, on the rushes round the margin of a small pond, -a great many patches of eggs, and shortly after observed many of the -_Sialis lutarius_ depositing them. - -‘They form large patches of from two to three inches in length, -generally encircling the whole rush near the top, but sometimes -deposited on one side only, and extended to about a line in breadth. - -‘I counted 100 in a square line, so that each batch may be fairly -considered to contain from 2,000 to 3,000 eggs; the greater portion of -which must consequently perish either in the egg or larva state; as, -common as the insect is, and widely distributed throughout the country, -we should be perfectly overwhelmed with the swarms of the perfect -insect if such were permitted, when it is considered that round this -one small pond there could not have been less than 100 patches of them. - -‘The eggs are of a very singular form, and placed in a slanting -position. - -‘The females, while depositing them, appeared perfectly motionless on -the rush, and varied considerably in size, being from five lines to -nearly double that in length. Some parts of the patches of eggs are of -a much lighter colour than the rest. - -‘On May 3 I found many of the eggs hatching, the little larvae tumbling -about in great numbers, with their bodies erected like [the larvae of] -the _Staphylinidae_. - -‘On putting them into water they swam about with the greatest activity, -wriggling and undulating their bodies about much like a serpent or the -tadpoles, and working their legs at the same time[66].’ - -The author draws attention to the disproportionately large head of the -larvae, which, however, he did not describe, as he had ‘brought some of -them alive, and some eggs for exhibition.’ - -Sialis larvae occur in most ponds with muddy bottoms. They may be taken -by scooping up some of the mud in a long-handled spoon--a most useful -instrument for the collector--and washing it, or by throwing in the -drag, and bringing to land a mass of water-weed, roots and all. A few -may generally be detected near the roots. They may be picked up with a -small pair of forceps, or with a brush, and dropped into a bottle; or, -better still, into separate tubes; for they are fierce and voracious, -and, failing other food, by no means indisposed to prey on each other. - -Their general appearance, and especially their powerful mandibles, give -them some resemblance to the larvae of a water beetle, for which a -celebrated naturalist not unnaturally took them, when he began to study -them. And this would seem to be the opinion of some mounters, for I -have a slide of the mouth parts of this larvae, labelled ‘Mouth parts -of the larvae of a water beetle.’ It was not till I had broken up a -good many Sialis larvae that I found out what the slide really was. - -These larvae may be kept alive in small bottles of water, if they -are supplied with food. They will eat Chironomus larvae and those of -Tanypus. Professor Miall has found that they will eat caddis-worms and -May-fly larvae. Probably, no small aquatic creatures that they can -overcome are safe from them. - -A larva that is full-fed, and ready to change to become a pupa, will -measure about an inch in length or a little more (Fig. 85). The general -colour is brownish, with dark markings. The legs are powerful, and our -lens will show us that they end in two strong curved claws. From each -of the first seven segments of the abdomen are given off a pair of -jointed tracheal gills or breathing-organs, which are directed upwards -and backwards when the larva is at rest--a rare occurrence--but which -wave to and fro in the water when the creature is swimming. - -From this fact has arisen the statement found in most books that the -larva uses these gills not only for respiration, but for locomotion. -Professor Miall has come to a contrary conclusion, and, as he has -kindly informed me, is confirmed in his opinion by the weakness of the -muscles. - - [Illustration: - - FIG. 85.--Larva of Sialis (enlarged).] - -It will be well to make repeated observations till we are satisfied -on the subject. When these larvae are kept, the conditions necessary -to provide them with food and to keep the water aërated by means of -growing vegetation are unfavourable to close observation. It will, -therefore, be necessary to remove one or more of these larvae to a -bottle in which there is nothing but pure water. - -The work is now rendered much easier. There is nothing to obstruct. As -soon as the larvae reach the bottom they will walk round and round, -giving us a good opportunity of watching them. In swimming--which may -be backwards as well as forwards--the abdomen is waved from side to -side. To see the backward motion one need only put a dipping-tube or a -pencil, or the like, in front of the larva, so as to bar its progress. -The creature will retreat a step or two, and then, with a flourish of -the abdomen, dart back through the water. The larva will sometimes wave -the abdomen up and down, just as one may see a Chironomus larva do when -it has affixed its dwelling to the side of the glass, and this motion -probably assists the process of respiration. - -When the larvae have been watched under the conditions above described, -I have never been able to detect independent motion of the gills. But -it is better that every one should observe for himself, and draw his -own conclusions from what he sees. - -Now let us examine a specimen more closely with the lens, or under the -dissecting microscope. The mouth parts may be broken up separately, or -a little careful manipulation will enable us to see the chief features -without injuring the specimen. The head is strong and massive, and -the group of ocelli, or simple eyes, may be clearly made out. The -antennae bear a small pencil of hairs, no doubt sensory in function, -at the extremity, but careful management of the light will be required -to distinguish them. The mandibles are extremely business-like -instruments, and each bears two strong teeth on the inner side. Next -come the maxillae, with their palps, each of which has an appendage, -while each maxilla carries three strong spines. The labium, with its -palps, and the mentum, with its saw-like notchings, may be plainly seen. - -The three segments of the thorax offer no difficulty. The legs are -worth more than a cursory examination from their apparatus of spines -and double fringe of hairs. Nine body-segments succeed to the thorax, -and behind these is a long tail-like organ, which some authors consider -represents a tenth segment. - - [Illustration: - - _h_ _t_ 1 2 3 4 5 6 7 8 9 tail - -- ----- -- -- -- -- -- -- -- -- -- ------ - | | | | | | | | - - - FIG. 86.--Diagram of Sialis larva, showing arrangement - of gills (represented by vertical lines). _h_, head; - _t_, thorax; 1–9, segments of abdomen.] - -The gills are seven on each side, and are given off from the spaces -in front of the first seven segments of the abdomen. Each gill is -five-jointed--an unusual arrangement, for the gills of the larvae of -Limnobia and Gyrinus are without joints. With the half-inch Leitz the -branching tracheal tube in the gill may be seen, as well as the double -fringe of hairs and the long hairs at the extremity. The tail-like -organ, though without joints, bears a close resemblance to the gills. -It has two tracheal tubes running through it, and it is fringed on both -sides with hair. Indeed, Professor Miall, F.R.S., compares it to ‘two -ordinary tracheal gills completely fused together.’ The first glance -will convince the observer that the comparison is just. - - [Illustration: FIG. 87.--Pupa of Sialis.] - -The pupa (Fig. 87) need not detain us, for the larva undergoes its -transformation in the ground, not in the water, where it could be -watched. But it is interesting to notice that the legs and wings are -enclosed in separate cases, and that the segments of the abdomen bear -spines. These spines are extremely serviceable to the pupa when making -its way out of its cell to emerge as a perfect insect, which is well -known, especially to fishermen, as the Alder-fly. It may be found near -streams, and rarely uses its wings. - -_Ptychoptera paludosa_ is a small Crane-fly, with an aquatic larva -which will repay observation. It is one of the group generally called -‘rat-tailed maggots,’ from the peculiar character of the breathing -apparatus, which consists of a retractile tube at the end of the -abdomen. It is, I believe, better known to some dealers than the larva -of the Drone-fly, the rat-tailed maggot of Réaumur. A few months ago I -wanted some Drone-fly larvae, and asked a dealer to supply me. When the -larvae arrived and were turned out for examination, they proved to be -Ptychoptera larvae--which I did not want. I naturally wrote to point -out the mistake; and was told, in reply, that the larvae sent were the -only ‘rat-tails’ known to my correspondent. - -This larva is a mud-dweller, and is best captured by scooping up -surface mud near the banks of pools and ditches, just where the water -shallows on to the shore. This should be washed in a small dish or -saucer, so as to carry away the mud and leave the larvae wriggling -on the bottom. They may be picked up with a brush and dropped into a -bottle for transport home. - -There is not the slightest difficulty about keeping them for -observation. A bottle of the capacity of six or eight fluid ounces -will make a good aquarium for a dozen or even twenty. The bottom should -be covered to the depth of about an inch with mud fairly rich in -organic matter. My own plan has been to use the accumulation from the -bottom of a large aquarium. In this the larvae will bury the body, and -feed, the tail protruding and thrust up to the surface of the water, of -which there should be about two inches above the mud. - -This is a liberal allowance of space. A couple of these larvae lived -with me for some months in a glass capsule two inches in diameter and -three-quarters of an inch in height. The mud at the bottom and the -water covering it together measured about half an inch. Both pupated, -and in due time from the pupa cases a perfect insect came out. - -But that larvae may pupate, they require to be well fed. How shall -we know when the bulk of the nourishment has been extracted from the -mud? From the castings of the larvae; and these, though of a different -shape, are as easy to be distinguished as the castings of the earthworm -in the garden or those of the lobworm on the seashore. All the mud that -passes through the bodies of the larvae is discharged in the form of -tiny hard, cylindrical pellets; and when the mass consists of these -pellets it should be changed, or the larvae will go short of food. They -will, however, support long fasts. - -From Fig. 88 we may get a good idea of the appearance of the larvae -when kept in confinement. The figures are rather less than natural -size, and all the attitudes were sketched from life. One is seen -extended on the bottom; two are partially buried in the mud, with the -breathing-tube protruding. The larva on the mud, and bent into curves, -is just about to rise to the surface; others are shown in the act of -rising, while one has its breathing-tube raised above the surface, and -another is attached by the breathing-tube to the side of the glass -vessel. The larva with the star-like process at the end of the tail is -that of Odontomyia, a large bee-like fly. - - [Illustration: FIG. 88.--Larvae of _Ptychoptera - paludosa_ (from life).] - -A larva of good size, like that of Ptychoptera, is especially easy to -examine; and by reason of its transparency the tracheal tubes may be -clearly traced. The under surface of the larva should be first looked -at, and its adaptation for existence in the mud of a pond-bottom will -be evident. The creature is legless, but possesses three pairs of -false legs armed with dark-coloured hooks, and each body-segment bears -a circle of stiff hairs, which enable the larva to travel through -the mud, in the same way that the earthworm moves through the soil. -Moreover, the segments between these circles are pretty thickly set -with hairs. - -The tracheal tubes run down on each side of the body, not in a direct -line, for there is a most ingenious arrangement by which contraction -and expansion of the larva, and the protrusion and retraction of -the tail, are provided for. One can easily discern that in most of -the segments the tubes are large, and that these large portions are -connected by smaller tubes, whence others are given off into the body. -These connecting-tubes are loop-like when the larva is of the normal -length, but are straightened out, thus adding to their length, when the -larva is extended. - -The opening and closing of these loops may be observed at leisure if -a larva be put in a long excavated slip, with some water, and then -covered with a plain glass slip. The two slips, fastened together with -small elastic bands, should then be laid on the stage of the dissecting -microscope for examination; or they may be held in the hands, and the -movements of the larva watched with the hand lens. - -In the posterior segments of the body the tracheal tubes run side by -side, while in the tail itself they are, so to speak, intertwined. When -the tip of the tail pierces the surface-film a fresh supply of air is -taken in. - -At the base of the extensile portion are two processes which diverge, -one on each side, at an angle of 45 degrees. These, according to a -German observer, are tracheal gills, and they are absorbed just before -the larva enters the pupal condition. - -Réaumur found these larvae plentifully in the Bois de Boulogne, and -gives a figure[67]. He was not, however, successful in rearing the fly. -Lyonnet not only took the larvae and kept them in an aquarium, but -watched their change into the pupal condition, and saw them emerge as -perfect insects. An abstract of this description will probably be of -interest. - - [Illustration: - - FIG. 89.--_A._ Ptychoptera larva (enlarged). - _B._ Tail, showing air-vessels (still more enlarged). - (After Lyonnet.)] - -He tells us that the larvae showed signs of changing into pupae in -June. The change was made without the larvae leaving the water, and -they underwent all their transformations in less than a fortnight. -At the approach of the change the larvae became whiter in colour, -but less transparent. Then they cast their skin, leaving therein the -air-vessels, or rather their external covering. After this last moult -was over, he was surprised to find that the tube which formed the tail -of the larva, and by which it took in a supply of air, though it serves -the same purpose in the pupa, is attached to the thorax, near the top -of the head[68]. Lyonnet appears to have overlooked the fact that there -was a second and shorter tube given off from the thorax, which most -observers consider to be functionless (Fig. 90). - - [Illustration: FIG. 90.--Pupa of Ptychoptera. (After - Lyonnet.)] - -Strange as is the larva, the pupa is stranger still, and seems even -better adapted for existence in the mud. The hinder part of each -segment of the abdomen is thickened and studded with chitinous -projections. This thickening is more marked, and of greater extent in -each succeeding segment, reaching its greatest development in the last -segment, which is armed with hooks. The body part of each segment bears -rows of smaller spines, so that this pupa should have little or no -difficulty in moving through pretty thick mud. - -Several of these Crane-flies have passed through all their stages with -me, and in nearly every case the transformation from pupa to perfect -insect was made in water--in a tube three inches long, with a diameter -of about an inch. The larvae were taken about the middle of September. -My notes show that the first pupated on November 17, and the first fly -came out on November 25. - -The long breathing-tube of the pupa was several times purposely -displaced from its position on the surface. The creature was evidently -incommoded, and twisted itself into strong curves; the head was thrown -from side to side till part of the breathing-tube was raised above the -surface and adhered to the side of the glass tube. Nor did the efforts -cease till a considerable portion of the tube was in free communication -with the air. This would seem to show that the air-supply is taken -through the bladders which appear at irregular intervals in the -breathing-tube, and not at the tip, where the keenest observers have -failed to find an opening. - - - - - INDEX - - - Acridiidae, 80. - - Alder-fly, larva of, 177; - pupa of, 182. - - American Cockroach, 74. - - Amphipods, 141; - Rev. T. R. R. Stebbing on, 141. - - Aquaria, description of, 20. - - Arachnoidea, 96. - - _Argyroneta aquatica_, 108; - De Geer on, 109; - nest of, 110. - - Arthropods, 27; - divisions of, 28; - description of, 29. - - Ascidians, Darwin on, 13. - - _Asellus aquaticus_, description of, 153. - - Assassin Worm, 158. - - Aurivillius, Dr., on Crabs, 150. - - - Bate and Westwood on Gammarus, 147; - on Talitrus, 151. - - Bateman, Rev. G. C., on Hydrophilus, 50; - on Nepa, 91; - on China Marks, 171. - - Beakers, 21. - - Beetle Mite, 119. - - Belt on Blatta, 67. - - Black Beetle, 63. - - Black-bobs, 64. - - Blackwall on Spiders, 101, 102. - - _Blatta orientalis_, description of, 63, 66; - Gilbert White on, 64; - Dr. Sharp on, 65; - Belt on, 67; - Sir J. Lubbock on, 68; - anatomy of, 68; - breathing of, 70; - Swammerdam on, 74; - Professor Plateau on, 74. - - Book Scorpions, 96. - - _Brachelytra_, 59. - - Broad-clawed Porcelain Crab, 139. - - Brown China Mark, 172. - - Brushes, 23. - - Bugs, 86. - - Burgess, Mr., on larva of Dytiscus, 160. - - Butler, Dr., on Spiders, 100. - - Butler, Mr. E. A., on Forficula, 79. - - - Capsules, 21. - - _Carcinus maenas_, description of, 136. - - Centipedes, 122; - marine, 125. - - Cerci, 47. - - Chelate, meaning of word, 132 _n._ - - China Marks, 171; - Rev. G. C. Bateman on, 171; - De Geer on, 172. - - Cockroach, 63. - - Cocktail Beetle, 57. - - Coleoptera, 32. - - Collecting, method of, 25. - - Corixa, 94; - Graber on, 95; - Sir J. Lubbock on, 95. - - Crab, Shore, 136; - Porcelain, 139. - - Crane-fly, 165. - - Crustacea, 128. - - - Daddy-longlegs, 103. - - Dallas on Ocypus, 61. - - Darwin on microscopes, 12; - on Ascidians, 13. - - Devil’s Coach Horse, 57. - - Dipping-tubes, 23. - - Dissecting microscope, 18. - - Dissection, mode of, 37. - - Diving Spiders, 108. - - Dugès on Water Mites, 117. - - Dung Beetle, 119. - - _Dytiscus marginalis_, 31; - etymology of, 33 _n._; - breaking of shells by, 33; - Sowerby on, 34; - description of, 35; - food of, 36; - anatomy of, 37; - habits of, 41; - Kirby on, 41; - Sir J. Lubbock on, 42; - Professors Lowne and Miall on, 45; - Dr. Sharp on, 47; - abdomen of, 47; - breathing of, 48; - larva of, 157; - Swammerdam on, 158, 159; - Mr. Burgess on, 160. - - - Earwig, 75. - - Edriophthalma, 129. - - Elytra, 41. - - _Epeira diadema_, description of, 98; - web of, 98; - J. A. Thomson on, 100; - Dr. Butler on, 100; - Blackwall on, 101, 102; - mode of taking its prey, 102; - Hudson on, 103; - feet of, 104; - spinnerets of, 105. - - Evans, W., on Sialis, 177. - - - _Field_, the, quoted, 33, 35. - - Forceps, 22. - - _Forficula auricularia_, 75; - Kirby and Spence on, 76; - De Geer on, 76; - young of, 76; - forceps of, 77; - anatomy of, 77; - Butler on, 79; - Dr. Sharp on, 79. - - Formalin, 24. - - Forty-legs, 122. - - Fresh-water Shrimp, 142. - - - _Gamasus coleoptratorum_, 119. - - _Gammarus marinus_, 146; - Dr. J. Salter on, 147. - - _Gammarus pulex_, 142; - anatomy of, 144. - - Geer, De, on Forficula, 76; - on Locusta, 80; - on Water Mites, 116; - on Beetle Mites, 120; - on Lithobius, 123; - on Julus, 126; - on larva of Limnobia, 167; - on Paraponyx, 172. - - Geophilus, 124. - - _Geophilus crassipes_, 125; - Mr. Pocock on, 125. - - Glass block, 22. - - Glass box, 22. - - Glass slips, 22. - - Gosse on Prawns, 133. - - Graber on Corixa, 95. - - Grasshopper, Great Green, 80. - - Great Water Beetle, 49. - - - Hart, Mr., on Paraponyx, 173. - - Harvestmen, 96. - - Hemiptera, 86. - - Hill, Dr., on Nepa, 90. - - Hudson on Spiders, 103. - - Hundred-legs, 122. - - Hunting Spiders, 98. - - Hydrachna, 113. - - _Hydrachna globula_, 118 _n._ - - Hydrophilus, larva of, 164; - Lyonnet on, 164. - - _Hydrophilus piceus_, 49; - Bateman on, 50; - legs of, 53; - Simmermacher on, 53; - breathing of, 54; - cocoons of, 54; - Lyonnet on, 54. - - Hymenoptera, wings of, 170. - - - Idotea, 143. - - _Idotea pelagica_, 155. - - Illinois State Laboratory, mode of collecting in, 25. - - ‘Insects,’ 27; - divisions of, 32. - - Invertebrates, 28. - - Isopods, 152. - - - Julus, 121, 124. - - _Julus terrestris_, 126; - De Geer on, 126; - Dr. Sharp on, 126. - - Jumping Spiders, 105. - - - Kew, Mr., on dispersal of shells, 130. - - Kirby on Dytiscus, 41; - on Ocypus, 59; - on Forficula, 76; - on Locusta, 83; - on insect noises, 84; - on Salticus, 107. - - Knives, 24. - - - Land Bugs, 86. - - Leaping Orthoptera, 79. - - Leitz, lenses of, 16. - - Lichtenstein on Locusta, 83. - - Limnaea broken by Dytiscus, 33. - - _Limnobia replicata_, larva of, 165; - De Geer on, 167; - pupa of, 168. - - _Lithobius forficatus_, 122; - De Geer on, 123; - Dr. Sharp on, 123. - - _Locusta viridissima_, 80; - Dr. Sharp on, 80, 85; - De Geer on, 80, 83; - Westwood on, 81; - Kirby on, 83; - Lichtenstein on, 83; - ear of, 85. - - Locustidae, 80. - - Lowne, Professor, on Dytiscus, 45. - - Lubbock, Sir J., on Dytiscus, 42; - on Blatta, 68; - on Corixa, 95; - on Opossum Shrimp, 135. - - Lyonnet on larva of Hydrophilus, 164; - on Ptychoptera, 186. - - - Magnification, power of, 15 _n._ - - Mainland, Mr. G. E., on Water Mites, 118. - - Malacostraca, 128; - Rev. T. R. R. Stebbing on, 128. - - Margined Water Beetle, 31. - - Masking Crabs, 150. - - _Melicerta janus_, 150. - - Miall, Professor, on Dytiscus, 45; - on Sialis larvae, 179, 181. - - Microscopes, use of, 11; - description of, 15. - - Millepedes, 121, 125. - - Mites, description of, 112. - - Model, a calico, 30. - - Myriapods, 96, 120. - - Mysis, 135. - - - _Nature Notes_ on Millepedes, 121. - - Needles, 23. - - _Nepa cinerea_, 86; - mode of keeping, 88; - Swammerdam on, 89; - Dr. Hill on, 90; - Rev. G. C. Bateman on, 91; - anatomy of, 91. - - Noises made by insects, 84. - - _Notonecta glauca_, 93. - - - _Ocypus olens_, 57; - Kirby on, 59; - as a pet, 59; - Dallas on, 61; - larva of, 61. - - Opossum Shrimp, 135; - Sir J. Lubbock on, 135. - - _Orchestia littorea_, 151. - - Orthoptera, 63. - - Ovipositors, 82. - - - _Palaemon serratus_, 129. - - _Palaemonetes varians_, 130. - - _Paraponyx stratiotata_, 171; - De Geer on, 172; - Mr. Hart on, 173; - anatomy of, 174. - - Peripatus, 30; - Professor Sedgwick on, 31. - - _Periplaneta americana_, 74. - - Pholcus, 103. - - Phylum, definition of, 27. - - Planorbis broken by Dytiscus, 33. - - Plateau, Professor, on Blatta, 74. - - Pocket lens, description of, 13. - - Pocock, Mr., on Geophilus, 125. - - Podophthalma, 129. - - _Porcellana platycheles_, 139. - - Prawns, 129; - Gosse on, 133; - Sowerby on, 133. - - Ptychoptera, larva of, 182; - pupa of, 187; - Réaumur on, 185; - Lyonnet on, 186. - - - Quekett Microscopical Club, incident at, 20. - - - ‘Rat-tails,’ 182. - - Réaumur on Ptychoptera, 185. - - Robertson, Mr., on Talitrus, 151. - - - Salter, Dr. J., on Gammarus, 147. - - _Salticus scenicus_, 105; - Kirby and Spence on, 107; - foot of, 108. - - Sand-hopper, 151. - - Scorpions, 96. - - Sedgwick, Professor, on Peripatus, 31. - - Sharp, Dr., on Dytiscus, 47; - on Blatta, 65; - on Forficula, 79; - on Locusta, 80, 85; - on Lithobius, 123; - on Julus, 126; - on wings of Hymenoptera, 170. - - Shells broken by Dytiscus, 33; - Mr. Kew on dispersal of, 130. - - Shore Crab, 136. - - Shore-hopper, 151. - - Shrimp, 132. - - _Sialis lutarius_, larva of, 177; - W. Evans on, 177; - anatomy of, 180; - pupa of, 182. - - Sicarius, 158. - - Simmermacher on Hydrophilus, 53. - - Sirex, 82. - - Sowerby, G. B., on Dytiscus, 34. - - Sphaerium, 130. - - Sphaeroma, 155. - - Spiders, general description of, 96; - Trap-door, 97; - Hunting, 98; - Garden, 98; - Jumping, 105; - Diving, 108. - - Stebbing, Rev. T. R. R., on etymology of Dytiscus, 33 _n._; - on Malacostraca, 128; - on meaning of _chelate_ and _sub-chelate_, 132 _n._; - on Amphipods, 141. - - Stewart, Professor, incident of, 20. - - Stilopyga, 63. - - Swammerdam on Blatta, 74; - on Nepa, 89; - on Water Mites, 114; - on Woodlice, 156; - on Dytiscus larva, 158, 159. - - - Tailed Wasp, 82. - - _Talitrus locusta_, 151; - Bate and Westwood on, 151; - Mr. Robertson on, 152. - - Tanypus, larva of, 176. - - Tegetmeier, Mr. W. B., on destruction of shells, 34. - - Thomson, J. A., on Spiders, 100. - - Trap-door Spider, 97. - - - Vertebrates, 28. - - - Wart-eater, 81. - - Water Beetle, Margined, 31; - the Great, 49. - - Water Boatman, 93. - - Water Bugs, 86. - - Water-devil, 157. - - Water Mites, 113; - Swammerdam on, 114; - De Geer on, 116; - Dugès on, 117; - Mainland on, 118. - - Water Scorpion, 86. - - Water-tiger, 157. - - Westwood on Locusta, 81. - - White, Gilbert, on Blatta, 64. - - Wing-cases, 41. - - Wireworm, 126. - - Wood, Rev. J. G., on lens stand, 15. - - Woodlice, 155; - Swammerdam on, 156. - - Worms, 29. - - Wright, Mr. L., on microscopes, 16. - - - Zeiss, lenses of, 15. - - - THE END. - - -FOOTNOTES: - -[1] Darwin, _Descent of Man_ (2nd ed.), p. 159, note 23. - -[2] The power of magnification of a lens is the ratio of its focal -distance to 10 inches. Thus a lens of 1 inch focus (or focal distance) -magnifies 10 times (written × 10, or ten diameters); one of ½ in. focal -distance, 20 times, and so on. - -[3] _A Popular Handbook to the Microscope_, p. 39. - -[4] _Journal of the Quekett Microscopical Club_, v. 148. - -[5] _Ponds and Rock Pools_, p. 17. - -[6] _Bulletin of the Illinois State Laboratory of Natural -History_, iv. 158. - -[7] ‘Dytiscus’ is written of set purpose. It is not, as some people -tell us, a miswriting for Dyticus; but a properly formed diminutive, -from the Greek _dutēs_ = a diver; like _paidiskos_ = a little boy. -Linnaeus consistently calls the genus Dytiscus from 1735 onwards. -Dyticus only dates from Geoffroy’s _Histoire Abrégée des Insectes_, -first published anonymously in 1762. On this question of nomenclature I -am glad to have the support of the Rev. T. R. R. Stebbing, F.R.S., who, -in answer to my inquiries, kindly wrote, ‘Darwin uses “Dytiscus” in the -_Origin of Species_, and I should decidedly recommend its being upheld.’ - -[8] April 4, 1896. - -[9] _Popular History of the Aquarium_, p. 258. - -[10] May 2, 1896. - -[11] International Science Series, No. lxv. - -[12] _Aquatic Insects_, pp. 55, 56. - -[13] _Zeitschrift f. wiss. Zoologie_, Bd. xl. S. 481. - -[14] _Mémoires du Muséum d’histoire naturelle_, xviii. 454 sqq. - -[15] I have purposely given _Blatta_ as the generic name, rather -than _Stilopyga_, which should properly be used, as the former is -only employed in very recent literature. - -[16] Miall and Denny, _The Cockroach_, p. 20. - -[17] _Cambridge Natural History_, v. 231. - -[18] _The Senses of Animals_, p. 44. - -[19] _Cambridge Nat. Hist._ v. 223. - -[20] _Book of Nature_, p. 94. - -[21] This refers to the gizzard. _Echinus_ was used to denote the -third stomach of Ruminants (now called the manyplies), because it was -thought to resemble a hedgehog rolled up. - -[22] Miall and Denny, _The Cockroach_, p. 118 (note). - -[23] _Introduction to Entomology_, letter xi. - -[24] _Proceedings of the Zoological Society_, 1892, p. 586. - -[25] _Our Household Insects_, pp. 159–163. - -[26] Kirby and Spence, _Introd. to Entomology_, ed. 1870, p. 484. - -[27] _Cambridge Natural History_, v. 318. - -[28] _The Senses of Animals_, p. 75. - -[29] J. Arthur Thomson, _Outlines of Zoology_, p. 288. - -[30] _Science for All_, ii. 178. - -[31] _British Spiders_, p. 10. - -[32] _British Spiders_, p. 359. - -[33] _Naturalist in La Plata_, p. 188. - -[34] _Mémoires_, vii. p. 304 sqq. - -[35] _Book of Nature_, pp. 101, 102. - -[36] _Mémoires_, vii. 144, 145. - -[37] The specimen was kindly identified for me, by Dr. Trouessart of -Paris, as a nymph of _Hydrachna globula_ (Dugès), and has been -deposited in the British Museum (Natural History). - -[38] _Mémoires_, vii. 123–128. - -[39] _Cambridge Natural History_, vol. v. ch. ii. - -[40] _Nature_, Dec. 12, 1895. - -[41] _Mémoires_, vii. 569. - -[42] _Crustacea_, p. 7. - -[43] _Crustacea_, p. 225. - -[44] International Science Series, No. lxxv. - -[45] ‘A limb is _chelate_ when it has joints that will act -together like a pair of tongs. Generally this character is produced by -the hinging of the seventh joint a considerable way down on the side -of the sixth. When the seventh joint, or finger, can be folded back -upon the sixth, although the latter is not produced into any thumb-like -process to oppose it, the limb is then said to be _sub-chelate_, -the claw being in that case partial, though often extremely efficient.’ -Stebbing, _Crustacea_ (International Science Series, lxxiv), p. 45. - -[46] _Popular History of the Aquarium_, p. 223. - -[47] Lubbock, _Senses of Animals_ (International Science Series, -lxv.), p. 93. - -[48] _Aquarium_ (ed. 1856), pp. 41, 42. - -[49] _Crustacea_ (International Science Series, lxxiv), pp. 8, 9. - -[50] Bate and Westwood, _British Sessile-eyed Crustacea_, i. 8. - -[51] _Trans. Connecticut Academy_ (1882), iv. 274, 275, note. - -[52] _Ponds and Rock Pools_, p. 118. - -[53] _British Sessile-eyed Crustacea_, i. 21. - -[54] _Proceedings Nat. Hist. Soc. Glasgow_, vol. i. pt. ii. n. s. -pp. 130–132. - -[55] _British Sessile-eyed Crustacea_, ii. 381. - -[56] _Book of Nature_, i. 174. - -[57] _Mémoires_, iv. 386. - -[58] _Proceedings Boston Society of Natural History_, xxi. 223–228. - -[59] _Natural History of Aquatic Insects_, p. 47. - -[60] _Mémoires du Museum_, xviii. 442, 443. - -[61] _Mémoires_, vi. 352–55. - -[62] _Diptera_, iii. 281. - -[63] _Cambridge Natural History_, v. 494. - -[64] _Mémoires pour servir_, i. 577 sqq. - -[65] _Bulletin of the Illinois State Laboratory of Natural -History_, iv. 167. - -[66] W. Evans, _Trans. Entomol. Soc._ (London), iv. 261. - -[67] _Mémoires pour servir_, t. vi. Plate 31. - -[68] _Mémoires du Muséum_, t. xix. pp. 103, 104. - - -Transcriber’s Notes: - - 1. Obvious printers’, punctuation and spelling errors have been - corrected silently. - - 2. Some hyphenated and non-hyphenated versions of the same words have - been retained as in the original. - - 3. 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