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+*** START OF THE PROJECT GUTENBERG EBOOK 78328 ***
+
+
+
+
+                          Transcriber’s Note
+
+
+  1. Certain typographic errors & hyphenation inconsistencies were
+     silently corrected.
+
+  2. The text version is marked up as follows:
+
+      (a) italics are indicated thus _italic_;
+
+      (b) small-caps are indicated thus +Small-Caps+;
+
+      (c) Images are indicated as [Illustration: (with narration.)]
+
+  3. Illustration captions have been standardised.
+
+  4. Table of Contents extended by adding references to the LIST OF
+     ILLUSTRATIONS, INDEX, and ADVERTISEMENTS.
+
+
+
+
+                     [Illustration: _Frontispiece._
+           +A Jelly-fish with the fry of the Horse-mackerel.+
+          (The fish have been relatively very much enlarged.)]
+
+
+
+
+                                  THE
+
+                       STORY OF LIFE IN THE SEAS
+
+                                   BY
+
+                    SYDNEY J. HICKSON, D.Sc., F.R.S.
+
+        _Professor of Zoology in the Owens College, Manchester_
+
+                     _WITH FORTY-TWO ILLUSTRATIONS_
+
+                                 LONDON
+                         GEORGE NEWNES, LIMITED
+                       SOUTHAMPTON STREET, STRAND
+                                  1898
+
+
+
+
+                         OUTLINE CLASSIFICATION
+                                   OF
+                    ANIMALS MENTIONED IN THIS BOOK.
+
+
+  PROTOZOA      {Foraminifers.
+                {Radiolarians.
+
+  PORIFERA       Sponges.
+
+                {Sea-anemones.
+  CŒLENTERATA   {Corals.
+                {Jelly-fish.
+                {Many of the Zoophytes.
+
+                {_Asteroidea_       Star-fishes.
+  ECHINODERMA   {_Echinoidea_       Sea-urchins.
+                {_Crinoidea_        Sea-lilies.
+                {_Holothuroidea_    Trepangs.
+
+  PLATYELMIA     Flukes, Tape-worms, Planarians.
+
+  CHÆTOPODA      Segmented Worms and Gephyreans.
+
+                {                  {Copepods.
+                {                  {Barnacles.
+  ARTHROPODA    {_Crustacea_       {Shrimps.
+                {                  {Crabs.
+                {_Insecta_          Halobates, &c.
+
+                {_Lamelli_          Bivalves.
+                { _branchiata_
+  MOLLUSCA      {_Gastropoda_       Whelks, &c., and Pteropods.
+                {_Cephalopoda_      Octopuses, Cuttlefishes, &c.
+
+  TUNICATA       Sea-squirts, Salps, Pyrosoma.
+
+                {_Pisces_           Fish.
+                {_Amphibia_         Frogs.
+                {_Reptilia_         Turtles, Crocodiles, Snakes.
+  VERTEBRATA    {_Aves_             Birds.
+                {                  {Whales, Porpoises.
+                {_Mammalia_        {Seals,
+                {                  {and the terrestrial Mammals.
+
+
+
+
+                               PREFACE.
+
+
+The story of the life of animals and plants in the sea is one with so
+many aspects, that it is difficult to choose the points that may be
+included, and those that may be omitted from a book intended for the
+general reader. To some the story of the food Fishes and the Whales is
+of the greatest interest; to others the beautiful shapes and colours
+of shells have a predominating fascination; and to those who have
+devoted themselves to geological study, the history of the animals that
+contribute to the formation of the reefs and the ocean-bed present
+features of special attraction. To many, then, the perusal of my book
+must lead to disappointment as no one of these aspects has been treated
+adequately; but if some new interest is awakened, some new train of
+thought quickened into life, one of the objects I had in view will have
+been gained.
+
+The book is only intended to be a sketch of some of the most important
+lines of scientific researches which are now being pursued by
+zoologists in many parts of the world. Discoveries, which are of the
+deepest interest to all intelligent minds, are in many cases described
+in books and periodicals that do not come within the reach of the
+general public. I have tried, therefore, to collect some of them into
+a small compass and describe them in language which I trust will be
+intelligible to those who have not been trained in the alphabet of
+zoological technicalities. The use of some long words was unavoidable,
+but I have endeavoured to explain them adequately either in the text or
+in the index.
+
+Some of the illustrations have been copied from the works of other
+Naturalists, and the sources from which they came are acknowledged in
+the list of illustrations; but the majority of them have been drawn,
+specially for this work, from specimens from the Manchester Museum or
+my own collections.
+
+                                                      SYDNEY J. HICKSON.
+
+_November 1897._
+
+
+
+
+                               CONTENTS.
+
+
+  CHAP.                                                             PAGE
+
+        LIST OF ILLUSTRATIONS                                          8
+
+     I. OCEANOGRAPHY                                                   9
+
+    II. SHALLOW-WATER FAUNA                                           23
+
+   III. SHALLOW-WATER FAUNA OF THE TROPICS                            55
+
+    IV. SURFACE-SWIMMING FAUNA (INVERTEBRATES)                        82
+
+     V. SURFACE-SWIMMING FAUNA (VERTEBRATES)                         118
+
+    VI. DEEP-SEA FAUNA                                               135
+
+   VII. COMMENSALISM AND PARASITISM                                  146
+
+  VIII. THE ORIGIN OF THE MARINE FAUNA                               172
+
+        INDEX                                                        180
+
+        ADVERTISEMENTS                                               184
+
+
+
+
+                        LIST OF ILLUSTRATIONS.
+
+
+  ILLUSTRATION                                                      PAGE
+
+  _Frontispiece._--A Jelly-fish with the fry of the Horse Mackerel
+   (from specimens captured by Mr F. W. Gamble off Valentia).          2
+
+  Fig. 1--Globigerina Shell                                           21
+
+  Fig. 2--Radiolarian Shells                                          22
+
+  Fig. 3--Common Pipe-fish (from Royal Natural History)               25
+
+  Fig. 4--Phyllopteryx (from Royal Natural History)                   26
+
+  Fig. 5--Diagrams of Eyes                                            27
+
+  Fig. 6--A branch of the Zoophyte Obelia                             30
+
+  Fig. 7--Medusa produced by Obelia                                   31
+
+  Fig. 8--A Bivalve Mollusc                                           35
+
+  Fig. 9--The common Sole                                             37
+
+  Fig. 10--The Angler (from Royal Natural History)                    38
+
+  Fig. 11--Vertical section of a Balanus (after Claus)                40
+
+  Fig. 12--Nauplius larva of a Balanus (after Groom)                  41
+
+  Fig. 13--Sea-urchin                                                 43
+
+  Fig. 14--Smooth-shelled Gastropod                                   47
+
+  Fig. 15--Spiny Gastropod                                            47
+
+  Fig. 16--A Cuttle-fish                                              49
+
+  Fig. 17--The Wrasse                                                 51
+
+  Fig. 18--The John Dory                                              54
+
+  Fig. 19--Polyp of a Madrepore Coral (after Fowler)                  58
+
+  Fig. 20--Chætodon                                                   62
+
+  Fig. 21--Globe-fish                                                 64
+
+  Fig. 22--Stereosoma                                                 67
+
+  Fig. 23--Coral-reefs                                                69
+
+  Fig. 24--Periophthalmus                                             74
+
+  Fig. 25--Free-swimming Copepod (after Claus)                        88
+
+  Fig. 26--Swim-bladder of Velella                                    96
+
+  Fig. 27--Solitary form of Salp                                      99
+
+  Fig. 28--Pteropod                                                  101
+
+  Fig. 29--Shells of Foraminifers                                    104
+
+  Fig. 30--Globigerina                                               105
+
+  Fig. 31--Young larva of a Star-fish                                111
+
+  Fig. 32--Pluteus larva                                             113
+
+  Fig. 33--Long-spined Barnacle-nauplius (after Chun)                116
+
+  Fig. 34--Sun-fish                                                  122
+
+  Fig. 35--The common Porpoise                                       129
+
+  Fig. 36--A deep-sea Fish (after Filhol)                            139
+
+  Fig. 37--Hermit-crab and Sponge                                    149
+
+  Fig. 38--Section through a Sponge showing Hermit-crab              150
+
+  Fig. 39--A Trepang                                                 153
+
+  Fig. 40--A Crab-gall                                               158
+
+  Fig. 41--A parasitic Copepod                                       169
+
+
+
+
+                    THE STORY OF LIFE IN THE SEAS.
+
+
+
+
+                              CHAPTER I.
+
+                             OCEANOGRAPHY.
+
+
+One of the most important facts that has been established by modern
+investigations of the Sea is that there is no region in its vast extent
+that is entirely devoid of animal life. The surface waters in the
+Equatorial calms and the ice-cold waters between the ice-bergs of the
+Arctic regions are densely populated by animals, large and small; the
+heavy and heated waters of the Mediterranean and Red Seas, and the cold
+and comparatively fresh waters of the Norwegian fjords, the shallow
+waters of the coasts and the greatest depths of the ocean-beds all
+present us with their characteristic forms of living creatures. There
+is no Azoic region known to us. Wherever we use the trawl or dredge
+we may expect to find some representatives of the various classes of
+marine animals. But the seas exhibit so many varying conditions that,
+as we might have expected, the animals that characterise one region are
+absent from another; and while, in some places animal life is abundant,
+in others it is very scarce; just as on land we find the grass-lands
+and forests teeming with life, and the great deserts and mountain tops
+inhabited only by a few solitary Lizards, Birds or Insects.
+
+In order that we may fully understand, then, the nature of the problems
+concerning the distribution of animals through the seas, it is of
+importance to consider first the conditions under which they must
+live in the different parts of the ocean. A knowledge of geography is
+clearly necessary for those who study the distribution of terrestrial
+and aërial animals, and equally necessary is it for those who wish
+to learn something about the distribution of the aquatic animals,
+to consider first of all the rudimentary principles of hydrography.
+The principal Sea areas of our globe may be roughly divided into two
+groups: namely, the great oceans--the Atlantic, Pacific and Indian
+Oceans--and the Inland seas, which are partly enclosed by land, such
+as the German Ocean, the Mediterranean Sea, and the Red Sea. Taking
+the areas of the great oceans and the seas together, we find that no
+less than 141 millions of square miles, or nearly three-quarters of the
+surface of the globe, are covered with water. Moreover, these great
+areas are continuous, so that it would be possible for an animal, other
+conditions being favourable, to pass from any one sea, such as the
+Black Sea, to any other, such as the Hudson’s Bay, without leaving the
+water,--an important fact in the consideration of the distribution of
+marine forms of life.
+
+The depth of the sea varies very considerably in the different parts of
+the world. In the inland seas the water is comparatively shallow, but
+in the great oceans it is very deep. In the middle of the North Sea,
+for example, we should not expect to find a depth much exceeding 250
+fathoms, but in the Atlantic or Pacific Oceans we have to pay out more
+than 2000 fathoms of the sounding-line before the bottom is reached. In
+some parts of the ocean-basins a few very deep holes or furrows may be
+found in which the depth exceeds 4000 fathoms, or 24,000 feet. One of
+these deep holes occurs in the Atlantic Ocean, a little to the North
+of the Virgin Islands in the West Indies, and there is another in the
+Pacific Ocean close to the coast of Japan; but the greatest depth that
+has yet been found is one recently discovered by H.M.S. “Penguin” off
+the coast of New Zealand of over 5000 fathoms. Apart, however, from
+the fact that these very great depths are only of local occurrence,
+the areas of deep water--that is, of more than 2000 fathoms--are so
+much greater than the areas of shallow water, that when we make a
+calculation of the average depth of the sea we find it is no less than
+2100 fathoms, or 12, 600 feet.
+
+The temperature of the sea is another feature which undoubtedly
+influences very greatly the character of its Fauna. The main source of
+the heat of the sea is the sun--for the heat derived from submarine
+volcanoes must be comparatively so small that we may omit it from
+consideration. Consequently we find that in the Equatorial regions the
+surface waters of the ocean are warmer than they are in the Temperate
+regions. These, again, are warmer than in the Arctic circles. But
+water is well-known to be a bad conductor of heat, and therefore
+the direct influence of the sun affects only the most superficial
+layers. In the Equatorial region of the Pacific Ocean, for example,
+the surface temperature is sometimes as high as 80° Fahr., at 100
+fathoms from the surface it is only 60°, at 400 fathoms only 45°, and
+at 1000 fathoms only a few degrees above freezing point. On the land
+the temperature falls as we pass from the coast to the high plateaux
+and mountains, and we find snow-capped mountains in Central Africa just
+as in Switzerland or Norway. In the sea the temperature falls as the
+thermometer is sent deeper from the surface. Just as on the land the
+snow line of the mountains is reached at high altitudes in the Tropics,
+at lower altitudes in the Temperate regions, and in the Arctic circle
+at the level of the sea, so in the sea the cold water that is found 500
+fathoms below the surface in the Tropics, reaches a higher level in the
+Temperate regions, and is at the surface in the Arctic circle.
+
+There is however one important point of difference between the
+distribution of these low temperatures on the land and in the oceans,
+in that they are broken in the former, and continuous in the latter.
+If we were to imagine an aquatic animal that could only live in
+temperatures below 35° Fahr., it would be able to travel below the
+surface from one pole to the other, or from one ocean to another; but
+it would be impossible for a terrestrial animal, exhibiting the same
+peculiarity, to leave the Arctic circle or the Alpine region without
+traversing lands where the temperature is higher than that which is
+necessary for its existence. It might be supposed from what has just
+been said that the temperature of the water at the bottom is constant
+for the same number of fathoms of depth. This is not, however, the
+case. The temperature of the sea-bottom of the great ocean-beds is
+approximately the same, varying from 28° F. in the Atlantic to 35°
+F. in the Pacific; but in places where main basins occur, surrounded
+on all sides by shallower ridges, the temperature of the bottom of
+the basin is the same as that of the lowest ridge. For instance, the
+temperature of the bottom of the Sulu Sea, lying between Borneo and
+the Philippines, is 40° F. at a depth of over 2000 fathoms. Again, the
+temperature of the Red Sea is as high as 70° F., although depths of
+1200 fathoms occur in its central portions; and this is the same as the
+temperature at the Straits of Babel Mandeb, which are 200 fathoms deep,
+and form the only outlet to the open ocean. These facts probably cause
+considerable modification in the character of the animals inhabiting
+such enclosed basins, but further investigations are needed before we
+can arrive at any very definite conclusions in the matter.
+
+Another important element that must be taken into consideration in
+studying the environment of marine animals, is the quantity and
+character of the salts held in solution by the sea-water. In the first
+place we must remember that the sea-water normally contains a far
+greater percentage of salts in solution than the water of rivers and
+lakes, and this causes it to be very much heavier. If a tumbler be
+half filled with sea-water, upon which some fresh water is slowly and
+carefully poured, there will be for some time very little mixture of
+the two fluids, the heavier sea-water remaining at the bottom, and the
+lighter fresh water at the surface. Now the density of the sea-water,
+or in other words the amount of salts in solution, is not the same
+over the whole world, and the differences that may be observed in
+this respect are due, in most cases, to the simple physical principle
+just enunciated. If we could imagine a river pouring its waters into
+a perfectly calm, tideless sea, we should be able to trace the fresh
+river water far away from the coast, for it would simply float on the
+heavier sea-water without mixing with it to any appreciable extent. In
+most cases, however, the tidal-waves, rushing up and down the river
+estuaries, stir up the fresh and salt water together, and cause a very
+considerable mixture, so that the water becomes either distinctly salt
+or brackish. Where very large quantities of fresh water are poured
+into the ocean, as, for example, at the mouth of the Amazon or the
+Mississippi, the surface water remains so fresh that the salt taste
+can hardly be appreciated at a distance of some miles from the coast.
+This fact sufficiently indicates the influence of great rivers upon the
+density or saltness of the sea-water in their neighbourhood, and the
+reader will be prepared for the statement that many inland seas, such
+as the Black Sea, are appreciably less salt than the great oceans.
+
+Again, the ocean water itself is not of the same density in all
+latitudes. In regions where there is a copious rainfall and the sea is
+not frequently disturbed by severe storms, the rain takes some time to
+mix with the heavier salt water on which it falls, and consequently
+there may always be discovered in these localities a thin stratum of
+comparatively fresh water on the surface of the ocean. In some inland
+seas where there is considerable evaporation and a slight rainfall, as
+for example, the Red Sea and the Mediterranean, the sea-water reaches
+an even higher degree of concentration than it does in the open ocean.
+The following table will serve to illustrate these facts:--
+
+Density of rain-water, 1·00.
+
+Density of the Black Sea surface, below 1·025.
+
+Density of the Atlantic Ocean surface (west of the Canaries), 1·0275.
+
+Density of the Mediterranean Sea, over 1·028.
+
+Density of the Red Sea, 1·030.
+
+Density of the bottom water of the Atlantic, 1·029 (west of the
+  Canaries).
+
+That the rate of movement of the water influences very largely the
+character of the animals that live in it, is a fact that it is not
+necessary to discuss fully in this place; but as it is undoubtedly one
+of the factors which must be taken into consideration in discussing the
+character and possible origin of the Fauna of any particular region,
+a brief survey must be given of some of the principal causes of the
+movements of the water and the characters of the tides and currents
+which are manifest in the sea. Twice every twenty-four hours the water
+of the sea rises and falls. This movement is due to the attracting
+influences of the sun and moon, and is, as is well-known, greater when
+the moon is full and when it is new than at the intermediate times. If
+the distribution of land and water on the surface of our globe were
+different, and a free waterway occurred round the world, right in the
+Equatorial band we should probably find a double tidal-wave rushing
+round the earth every twenty-four hours. As it is, however, the great
+tidal-wave is checked by the continents, and as it approaches the
+coasts is retarded and diminished in force. In Archipelagoes and along
+broken coast lines the tidal-waves produce true surface currents, which
+frequently run with great rapidity and exert considerable corroding
+action upon the rocks. In many estuaries and bays the tide rushes in
+with such force that the water is heaped up to a great height against
+the land. At the entrance to the Bay of Fundy, for example, the rise
+at spring-tides is no less than 70 feet, and at the Cardiff docks the
+difference of level between high and low spring-tides is 42 feet. The
+tumultuous ebb and flow of such masses of water along the coast is
+fatal to some forms of animal life and favourable to others, and so to
+some extent it modifies the character of the Fauna.
+
+In addition to the surface currents of the coast, produced by the
+tidal-waves, there are also the true ocean-currents, which must be
+briefly considered. They are caused by the winds which blow constantly
+in a definite direction across the oceans. The prevailing winds not
+only raise the sea into waves, but drive the superficial layers of the
+water over the subjacent layers in one direction. In studying a map
+of the great ocean-currents, we notice a well-marked one lying to the
+North of the Equator in both the Atlantic and Pacific. This flows from
+East to West and follows very closely the lines of the prevailing winds
+in that region. Similarly in the temperate regions of the Southern
+Hemisphere there is an ocean-current, flowing however in this case in
+the opposite direction--from West to East--and so corresponding with
+the trade-winds of that part of the world. The well-known Gulf-stream
+of the North Atlantic, although modified in some respects by other more
+complicated causes, also follows for part of its course the general
+direction of the prevailing winds.
+
+The currents just described are surface currents only, and do not
+affect to any great extent the mass of the subjacent waters in the
+ocean-basins. It is difficult to estimate the depth to which their
+influence reaches, but it is not probable that it extends more than 200
+fathoms below the surface. In addition to these, there is also a series
+of slow currents in the deep waters flowing in definite directions.
+In the Tropical regions the waters are constantly being heated by the
+sun, and passed away by the trade-winds to the North and South and
+ultimately towards the poles. In their long and complicated journey
+they are gradually cooled down until, in the regions of the ice-bergs,
+they reach a temperature just above the freezing point of sea-water.
+Here the water, being colder and therefore heavier than that of the
+other regions of the world, sinks to the bottom, and gradually returns
+in a deep-seated mass towards the Equator, where, welling up from the
+bottom, it replaces the heated layers of the surface. It is almost
+impossible to determine with accuracy the rapidity and exact direction
+of these deep-sea-currents. It is extremely probable that they are
+immensely modified by the irregularities of the bottom and the outline
+of the coast banks, but their exact topography must remain for the
+present one of the secrets of the abyss that are not revealed to us.
+All that can be said is, that the warm surface water which passes from
+the Tropics towards the North and South is replaced by deep-seated
+Polar currents, which account for the extremely cold water that is
+found at great depths in the ocean-basins, and also for some of the
+peculiarities of the marine Fauna, which will be referred to later on.
+
+The character of the sea-bottom in various parts of the world must
+be referred to before passing on, for there can be little doubt of
+the important effect it has upon the Fauna. In the neighbourhood of
+continents the bottom of the sea varies very considerably. The great
+rivers bring with them in suspension the products of the wear and tear
+of mountains and valleys; the coast line, washed by the continuous
+ebb and flow of the tides, contributes some of its substance to the
+formation of the sea-bottom; and the countless millions of animals
+and plants of the shallow waters leave their skeletons and shells as
+they die to form an integral part of the floor of the ocean. Thus
+the sea-bottom in the neighbourhood of the land is formed partly
+by terrigenous deposits, varying of course in character with the
+geological nature of the land itself, and partly by the animal and
+vegetable deposits of the coast. In some cases the deposits brought by
+the rivers can be traced in the sea-bottom for a very great distance
+from the coast. The characteristic mud of the Congo river can be traced
+600 miles from its mouth, and it is said that the Arabian Sea and the
+Bay of Bengal are carpeted for 1000 miles by the mud brought down by
+the Ganges and the Indus. Leaving out of consideration, however, for
+the moment the exceptional cases of such large rivers as these, we may
+say that the influence of the land deposits upon the character of the
+sea-bottom extends to a distance seawards of about 250 miles. If we
+had a complete and careful survey of all the coast lines, it would be
+possible for us to draw a line round the great continents marking the
+limit of the deposits of river and coast mud. This line has been called
+the mud-line by Mr John Murray, and, as he has clearly pointed out, it
+is characterised by an abundant and extremely interesting Fauna.
+
+The sea-bottom, then, within the limits of the mud-line, is very
+largely composed of deposits from the land brought down by the rivers.
+In some volcanic regions of the world this is, to a great extent,
+augmented by lava and water-logged pumice, and in other districts by
+the mud and stones dropped by the melting ice-bergs. The influence
+of animals and plants upon the formation of the sea-bottom is often
+very great indeed in shallow water, though it varies considerably in
+different parts of the world. In the neighbourhood of the British
+coast, for example, the sea-bottom is, in many places, carpeted with
+the calcareous Sea-weed, _Lithothamnion_,--in other places the
+dredge will come up crammed full of bivalve shells. But such instances
+as these in which the floor of the sea is covered with animal or
+vegetable shells, are comparatively rare and of small extent in the
+neighbourhood of land in the Temperate regions, and in nearly all
+localities the true terrigenous deposits can be readily obtained by
+the use of a small meshed dredge. In the warmer regions of the world,
+however, the sea-bottom in the shallow water is over great areas
+completely covered by animal and vegetable products. In the West
+Indies, and in some parts of the Eastern coasts of Tropical America, in
+the Eastern Archipelago and the coast of East Africa and its islands,
+Coral-reefs are found. These are entirely built up of the skeletons and
+shells of animals, and a few Coralline Algæ. In the vicinity of these
+reefs the floor of the sea is for miles carpeted with the broken-down
+skeletons of these animals, sometimes in the form of a fine coralline
+sand, sometimes of large lumps studded with knolls of living Corals,
+Molluscs, Sea-urchins, and other creatures. We find, therefore, in the
+warmer regions of the world immense areas of shallow water in which the
+terrigenous deposits take but a very small part in the formation of the
+sea-bottom, animal and vegetable life being so vigorous and active as
+to be able to form enough shells and skeletons to cover every available
+part of its surface.
+
+                       [Illustration: +Fig. 1.+
+               Globigerina Shell from a deep-sea ooze.]
+
+Far away from continental lands, and at great depths, the character
+of the sea-bottom completely changes. At a distance of 100 miles from
+the coasts of America or Europe, for example, the land deposits have
+already found their resting-place, and the animal life in the depths of
+the Atlantic is poor in skeleton-forming genera. However, the surface
+waters of the ocean teem with creatures of all sorts which, as they
+die, drop down their skeletons and shells in a gentle shower to form
+a fine deposit on the bottom. When we get beyond the mud-line, then,
+and use the dredging or sounding apparatus in depths of 1500 to 2500
+fathoms, we find that the bottom is largely composed of the shells of
+such surface animals as the Pteropods and Globigerinas, and according
+to the relative abundance of these forms it is called Pteropod Ooze or
+Globigerina Ooze. In still greater depths than these the character of
+the bottom again changes, and we find a deposit which is commonly known
+as the Red clay. The explanation of this change of character depends
+upon the fact that sea-water exercises a slightly solvent action upon
+carbonate of lime, and the shells of the Globigerinas and other forms
+are, in seas of a depth of over 2500 fathoms, dissolved before they can
+reach the bottom. The only shells that can survive this long journey
+are the siliceous shells of the Diatoms and Radiolarians, and in those
+parts of the ocean where these organisms live in abundance their empty
+shells form an important percentage of the composition of the Red
+clay. Over a very considerable area of the Pacific Ocean, however,
+the Red clay contains only a minute proportion of these shells, and
+its composition has given rise to a good deal of discussion among the
+authorities. It may be considered to be a conglomerate of the horny
+fragments of dead surface-living animals, of volcanic and meteoric
+dust, and of small pieces of water-logged pumice-stone.
+
+                       [Illustration: +Fig. 2.+
+             Radiolarian Shells from a deep-sea deposit.]
+
+In some of the very deep holes of the Pacific Ocean the mud is
+almost entirely composed of Radiolarian shells, and is then called
+“Radiolarian ooze”: and in the Southern Sea a mud called Diatom ooze
+has been found, which consists principally of the siliceous shells of
+these minute algæ. Notwithstanding these varieties of the mud, and
+others that space does not allow me to refer to at length, we may
+suppose that if the floor of any one of the great oceans were exposed
+it would have the appearance to a traveller of a vast desert-like
+expanse, without a stone, a rock, or a cliff to vary the monotony of
+the scene. At one time it was supposed to be an absolute plain, without
+any important change of level from the mud-line of one continental
+coast to the other; but the result of modern submarine explorations has
+been to prove that in all the great ocean-basins, hills and ridges, as
+well as troughs and deep holes occur, which break the monotony of the
+generally smooth and level character of the bottom.
+
+
+
+
+                              CHAPTER II.
+
+                         SHALLOW WATER FAUNA.
+
+
+Having considered thus briefly the general conditions under which the
+animals of the sea must live, we may now consider more in detail the
+special conditions of shallow water life.
+
+In water of only a few fathoms in depth, the direct light of the sun
+is capable of reaching and influencing all living things that occur,
+either at the bottom, at the surface, or in the intermediate waters.
+Great as the influence of direct sunlight must be upon animals, it
+is even greater upon plants. Nearly all the Sea-weeds are, like the
+plants of the dry land, dependent upon carbonic acid gas dissolved in
+the water for one of the most important constituents of their food,
+but it can only be absorbed by the plant in the presence of sunlight.
+It is possible, therefore, for Sea-weeds to flourish in the shallow
+waters of the sea, while they are necessarily absent from the deeper
+and darker regions to which the rays of the sun cannot penetrate.
+Everyone knows that in the shallow waters of our own coast there is
+in many places a dense tangle of Wracks and long, flat ribbon-like
+Sea-weeds growing on the bottom, and that on and amongst these weeds a
+rich harvest of animals awaits the eager shore collector. It is true
+that there are vast fields of sand on which the Sea-weeds are few and
+far between, but we may say that wherever they can obtain a secure
+foothold in the shallow waters of the British coast there they will
+grow and multiply in great profusion. We must not, however, jump too
+hastily to the conclusion that the same is true for all parts of the
+world. The British coasts are particularly rich in Sea-weeds, in fact
+a distinguished botanist once said that they probably present us with
+the greatest number of genera and species of any coast line of the same
+extent in the world. In the Temperate regions of both the Southern and
+Northern Hemispheres there is generally a rich Sea-weed flora, but in
+the warmer regions it is less luxuriant, and on the Coral-reefs of the
+Tropical seas it is remarkably poor.
+
+Turning our attention for the present to the Temperate regions, let us
+consider the influence that the Sea-weeds have upon the animals of the
+shallow waters. In the first place we find that they afford shelter and
+support for a large number of animals which could hardly live without
+them. In the roots of the weeds may be found little Crabs and Molluscs,
+which occur nowhere else; and clinging to the long waving branches are
+many forms of Sea-anemones, Zoophytes, flattened limpet-like Molluscs,
+Ascidians, and other forms of animal life. The great forests of weeds
+are also the haunts of many queer Fish, Prawns, Crabs, and Sea-slugs,
+which hunt their prey or hide from their enemies amidst the shelter of
+the stems and branches.
+
+                       [Illustration: +Fig. 3.+
+                        The common Pipe-fish.]
+
+Now many of these animals, which together make up the Fauna of the
+Sea-weed region, have assumed, in the course of the ages of evolution,
+not only the colours of the Algæ on which they live, but in some cases
+even forms which render them at first sight more like plants than
+animals. The slender Pipe-fish, for example, which is not uncommonly
+found amongst the bright green Sea-weeds of our coast, is wonderfully
+similar, both in form and colour, to the weeds on which it lives. The
+Sea-horses, which have such a curious form out of the water, in their
+natural surrounding resemble the weeds so closely that they may be
+easily overlooked. A still more remarkable example is to be found in
+the curious fish Phyllopteryx, in which the body is provided with long
+branched processes, making it we may suppose much more difficult to
+distinguish in its natural haunts than even the Pipe-fish or Sea-horse.
+
+                       [Illustration: +Fig. 4.+
+                            Phyllopteryx.]
+
+Many other examples to illustrate this feature of the Sea-weed Fauna
+could be quoted, but sufficient has been said at present if we have
+indicated to the reader the manner in which, by the indirect influence
+of light, the form and colour of animals may be modified for their
+life among the marine plants. The presence of light, however, modifies
+directly the character of the animals themselves in many respects.
+
+                       [Illustration: +Fig. 5.+
+  Diagrams of Eyes of _A_ Whelk, _B_ Lobster, _C_ Scallop, _D_ Fish.]
+
+The statement that many of the animals of the shallow water are
+provided with eyes because there is light is, when carefully examined,
+found to be strictly true, however anomalous it may seem to be. There
+must have been light in the shallow waters of the sea when the first
+primordial forms of life made their appearance, and it was this light
+which, step by step, led to the evolution of the most complicated and
+perfect forms of eye from the simplest pigment spot of the Protozoan
+to the eye of the Lobster and the Fish. We may say that all animals
+that freely swim in the shallow waters or that crawl and creep on the
+rocks and sands at the bottom are provided with eyes. The Fish are
+provided with a pair of eyes which present us with the same general
+features that we find in the other Vertebrates. Lobsters, Crabs and
+Prawns have each a pair of stalked eyes, which are probably as perfect
+in their functions as the Vertebrate eye, although built up on an
+entirely different model. Whelks, Winkles, and other Gastropods,
+although so slow in their movements, have each, upon or close to their
+tentacles, a pair of minute eyes, which are much simpler and probably
+far less perfect in form than the eyes of their more highly organised
+neighbours. Even the little Jelly-fish, Star-fish, Sea-urchins, and
+other creeping forms of life, are provided with specialised pigment
+spots, which we have good reason to believe enable them to perceive the
+rays of light.
+
+But we must notice that it is only the animals that are capable of
+locomotion from place to place that need these organs of vision,
+and that the stationary forms are blind. In the large class of the
+Lamellibranchs, for example, to which the Oyster and the Mussel belong,
+we find that with a few exceptions there are no eyes. These animals,
+after the first few stages of their life are past, settle down into
+the sand, or fasten on to a rock and remain there until their life
+is done. Their food, consisting of the minutest specks of animal and
+vegetable life, is brought to them by the sea-currents; they do not
+need nor desire to seek the society of their relations, and when their
+enemies approach they resign themselves almost without an effort to the
+inevitable. To such animals eyes would be useless, and so nature has
+withheld them.
+
+There are, however, a few Lamellibranchs that possess good eyes, eyes
+that are almost as complicated in their structure as the Vertebrate
+eye; and not a single pair only, but sixty, eighty, a hundred, or even
+more, may be found on a single individual. Such a Lamellibranch is the
+common Scallop which may be seen in many of our fishmongers’ shops.
+Unlike most of the group, this animal is able to make long flights
+through the water by the flapping together of its shells, and there
+can be no doubt that on the approach of danger it uses this method of
+locomotion for escape. One of its most deadly enemies is the Star-fish,
+which forces the shells apart and sucks out the flesh by means of its
+protrusible stomach. When a Star-fish is placed in an aquarium in which
+there are some Scallops, lying, as they do, on their sides, with the
+valves slightly open, showing the double row of gleaming metallic eyes
+on the margin of the mantle, the Star-fish immediately moves, with what
+in such an animal may be considered extraordinary rapidity, straight
+in the direction of the Scallop. Before, however, it reaches its prey,
+the coveted victim gives four or five vigorous flaps of its shells and
+swims away to another part of the tank. This suggests that the eyes
+of the Scallop are used in the light as a means of giving warning of
+the approach of an enemy, and they are found in the Scallops only,
+among common British bivalves, because they alone possess this power
+of swimming away. Of course if there were no light in the water the
+eyes would be useless, and it is an interesting fact that the Scallops
+which live in the darkness of the great depths of the ocean are quite
+blind.
+
+                       [Illustration: +Fig. 6.+
+                   A branch of the Zoophyte Obelia.]
+
+Very interesting examples of the connection between the presence of
+eyes and the power of locomotion are found among the sedentary or fixed
+forms of life. The great class of Sea-squirts or Tunicates includes a
+number of genera, most of which are, in the adult condition, immoveably
+fixed to the bottom, and in that stage have no eyes; but the eggs
+which they produce give rise to little creatures, like tad-poles in
+form, which swim about freely in the water. Each of these tad-poles
+has a large eye in its brain, which remains so long as the animal
+leads a free life. As soon, however, as it settles down upon the rock
+which is to become its permanent resting-place through life, the eye
+and the organ of locomotion, the tail, both degenerate and ultimately
+disappear. Again, we often find upon rocks, Sea-weed, old shells, and
+the like, some curious delicate branching organisms called Zoophytes.
+Notwithstanding their general resemblance in form to Sea-weeds, these
+Zoophytes are known to be animals. Each tuft or branch is formed by
+a number of delicate little Polyps, each with a crown of tentacles
+round a terminal mouth. The Polyp cannot move away from the branch it
+grows upon, nor the branch from the stem, nor the stem from the rock
+on which it rests, and none of these minute creatures are provided
+with eyes. There are, however, a few Zoophytes that give rise to buds,
+which grow into the form of minute Jelly-fish (or Medusæ, as they are
+called); and these, becoming detached from the parents, swim away and
+lead an independent existence. These Medusæ are in many cases provided
+with simple little eyes. During their short life they are drifted away
+by the sea-currents to some distance from their parents, and produce a
+number of eggs which are capable of developing into a new fixed colony
+of Polyps.
+
+                       [Illustration: +Fig. 7.+
+                      Medusa produced by Obelia.]
+
+We may consider it one of the maxims of Science that in a population
+of animals which possess eyes, colour as well as form is of extreme
+importance. As well as the alteration in form that takes place in the
+animals living among Sea-weeds, we find a modification in colour in
+the creatures dwelling among rocks or on the sand, so that they may
+resemble the ground on which they live. No more striking example of
+this could be found than in the common Shrimps of our coasts. Anyone
+who has watched them in the sea-pools must have been struck with their
+close resemblance to the sand. In fact it is only by close observation
+that they can be distinguished from it. In an aquarium, too, it
+may be observed how very much the upper sides of Soles, Flounders,
+Turbots and other flat fishes are like the sand in colour, while the
+under sides are almost invariably pure white. The black colour of the
+Lobsters, speckled and striped with blue, has a close resemblance to
+the holes and crannies of the rocks among which they live. The bright
+transparent green Prawns are almost invisible as they move about among
+the Sea-weeds, and Sea-slugs assume all manner of beautiful colours
+according to the ground on which they feed.
+
+On the Coral-reefs of the warmer regions of the world the pools that
+are left when the tide goes down are characterised by their brilliancy
+of colour. The bright purple, green, and yellow tips of the Coral
+branches, the red and bright green Sponges, and the white pieces of
+dead and broken Corals make up a scene of beauty which can only be
+compared with a bed of variegated flowers. Here the Fish, Prawns, and
+other moving animals have assumed the most gorgeous colours in patterns
+of spots and stripes which verily astonish the naturalist when he
+sees them for the first time. The great Sea-perches, with their sides
+covered with bright red or brown blotches, the curious Trigger-fish,
+with bright red, blue, or yellow bands crossing their bodies, the
+banded Lobsters, and the spotted Cuttlefishes, strange and conspicuous
+as they may seem when they are taken out of the water, are in life but
+in harmony with their surroundings, and, in reality, less conspicuous
+than they would be if less brilliantly arrayed.
+
+I remember on one occasion as I was watching some expanded Polyps in
+a little shore pool in the Tropics, I noticed something suddenly move
+close to the coral block on which I was standing. As there was no
+escape from the little pool, nor any holes in which the creature could
+hide itself from my observation, I searched with diligence to find it
+again, but for a long time without avail. Suddenly it moved again, and
+then I saw, resting on the brilliantly coloured corals, a remarkable
+little Shrimp called by zoologists _Stenopus_. Its body, which was
+almost transparent, was marked by a number of bands of a bright red
+colour, it had enormously long antennæ similarly banded, and its legs
+and body were covered with short red-tipped spines. When I succeeded in
+safely landing it in my collecting bottle I felt perfectly astonished
+that I had been so baffled by such a lovely little jewel, so bright, so
+strange, and so generally conspicuous did it then seem to be.
+
+The colours of the animals I have referred to hitherto may be accounted
+for by their need to escape the attention of their enemies, or to
+avoid detection in the pursuit of their prey; but the animal colour
+problem is not yet exhausted. The beautiful colours of the Anemones,
+Corals, Sponges and many other sedentary forms of animal life, and
+the marvellous patterns on the shells of Molluscs cannot be due to
+these causes. Many ingenious theories have been brought forward to
+explain away the difficulty, but none of them seem to be perfectly
+satisfactory, and consequently it is unnecessary to enunciate them in
+detail in this small book.
+
+The character of the bottom of shallow water, especially in the
+neighbourhood of the coasts, presents us with so many variations
+that it would be a long task to consider in detail all the different
+adaptations that the animals exhibit. The Fauna of the sand, shingle,
+and mud at the mouths of rivers, of the rocks of iron-bound coasts,
+and of the coral-reefs, each present us with many curious kinds of
+modification of form and structure. A brief reference to one or two
+characteristic regions must be made before passing on.
+
+The sandy bottoms which are so prevalent, not only upon our coasts,
+but in nearly all parts of the world, invariably support a Fauna with
+many curiously altered forms. In walking across the sands at low water
+we may have often noticed many worm-like and twisted columns of sand;
+these are the casts of the common Lug-worm, which is a favourite bait
+for many kinds of Fish. The Lug-worm lives in a U-shaped tube, which it
+forms from a slimy secretion of the body; it feeds by swallowing the
+sand in which it burrows, extracting from it as it passes through the
+intestine whatever animal or vegetable food it may contain. There can
+be little doubt that the sand is a very poor form of diet, and that
+an immense quantity must pass through the body of the animal compared
+with its weight in order to afford sufficient nourishment. It has been
+reckoned that as many as 82,433 casts may be found on an acre of sand
+where conditions are favourable for these Worms, and that they would
+weigh together nearly 2000 tons. This would mean that the whole mass of
+the sand would pass through the bodies of Lug-worms on an average of
+once in every twenty-two months.
+
+But the Lug-worm is only one of the many forms of life that burrow
+in the sand. A very large number of bivalve Molluscs live with the
+greater part of their bodies perpetually buried. Their organisation
+is such that their food and the water that is used for respiration
+can be brought to them by a tubular prolongation of the body called
+the siphon. Some of these animals live much deeper down than others,
+and while some have but feeble powers of moving either up or down in
+their burrows, others can penetrate to great depths with extraordinary
+rapidity.
+
+                       [Illustration: +Fig. 8.+
+ A Bivalve Mollusc, showing below the foot with which it burrows into
+                   the sand, and above the siphons.]
+
+The shell of a Lamellibranch, called the Razor-shell (_Solen_), is
+not an uncommon object of the sea-shore where stretches of sand occur.
+When the animal is alive it has the power of burrowing down so quickly
+that it is practically impossible for one man to capture a specimen
+by digging, when it is thoroughly alarmed. Occasionally, however, the
+sea itself, when lashed into fury by a storm, is a better digger than
+the Solen is a burrower; and after a heavy storm in the Isle of Man I
+have seen the shore littered with Solens scooped out of the sand by the
+force of the waves and cast up with lacerated shells to fall an easy
+prey to the Seagulls.
+
+The sandy bottoms in shallow waters are also the haunts of many kinds
+of Fish that are specially modified in form and colour to resemble
+their surroundings. The large family of the Skates have their bodies
+compressed from above downwards so that they can lie perfectly flat
+upon the sand. Their upper surface is deeply pigmented, giving them
+a general resemblance to the ground on which they lie; but to assist
+them in escaping observation they have a habit of shaking their fins in
+such a manner as to scatter a considerable quantity of sand over their
+bodies. Thus it can well be understood that in the dim light of the
+sea-bottom the little Fish and Shrimps, which form a large portion of
+their food, may approach quite close to them without being in the least
+aware of the danger into which they are running. The upper side of the
+Skate is also armed with a number of sharp and hard spines, and in some
+forms--called the Sting-rays--one of these, situated at the base of
+the tail, is much larger than the others, and provided with muscles so
+that it can be suddenly erected. In connection with this spine there is
+a poison-gland and duct. The wound that is inflicted upon the arms or
+feet of the fishermen by this formidable weapon of offence is said to
+be of a very serious nature.
+
+Some of the Skates, too, show another very interesting modification
+of structure, which, however, is not directly associated with their
+mode of life, but may be briefly referred to here whilst dealing with
+the family. This is the electric organ. In the younger stages of the
+common English Skate a small region of the muscular system on each side
+of the base of the tail becomes changed into an electric organ, but
+the discharges which it is able to give are so feeble that they can
+only be appreciated by a galvanometer. In the Torpedo, however, the
+electric organs are very large indeed, and situated one on each side
+of the head. They can give a shock which is powerful enough to kill
+small animals and to stun larger ones. With such a formidable weapon
+of offence and defence, it is clear that the need for active movements
+is considerably diminished, and the Torpedoes are described as being
+exceedingly slow in progression and incapable of the violent movements
+of other Skates.
+
+                       [Illustration: +Fig. 9.+
+     The Common Sole, showing both eyes on one side of the head.]
+
+The other Flat Fishes found on sandy bottoms belong to a different
+group altogether, and are characterised by their bony skeletons and
+other features. The Soles and their allies do not, like the Skates, lie
+flat upon their bellies, but are _laterally_ compressed and lie upon
+one side. The side which is habitually uppermost is of the colour of
+the sand, and the other almost invariably pure white. In the course
+of their development the Soles undergo very extraordinary changes in
+form to reach the perfectly flattened condition of the adult stage.
+These changes affect many of the organs of the body, but perhaps the
+most interesting of all is the history of the eyes. In the young Soles,
+which swim almost vertically, like the majority of fishes, there is
+one eye o each side of the head, but as they grow older and gradually
+take to the habit of swimming on one side, the eye of that side sinks
+down into the head, and rotating as it goes passes through to the other
+side. This process naturally leads to a considerable distortion of the
+skull, so that the bones of the adult Sole show as complete a want of
+symmetry as can be found in any Vertebrate.
+
+                      [Illustration: +Fig. 10.+
+                             The Angler.]
+
+Some of the Bony Fish, however, that live on the sand are flattened
+dorso-ventrally like the Skates. The Angler or Fishing-frog, for
+example, is a Flat Fish, which is perfectly symmetrical. Like the other
+Flat Fish its upper surface is coloured in such a manner as to resemble
+the ground on which it lives. Its great mouth, armed with formidable
+rows of sharp-pointed teeth, is directed upwards, and it receives its
+name from a curious tentacle terminating in a brightly-coloured knob
+which dangles over its mouth. The brightly-coloured knob looks no doubt
+a tempting morsel to the little Fish upon which the Angler preys, but
+the greed or curiosity, whichever it may be, that induces them to
+inspect the bait leads them to the fate which follows one snap of the
+great tooth-armed jaws.
+
+The Fauna of the shallow waters where rocks abound also possesses many
+peculiarities. In the first place we must remember that the rocks,
+being firm and hard, present a basis upon which many of the sedentary
+forms of life that would be swept away or smothered if they attempted
+to live on the ever-shifting sands, can fix themselves. Consequently
+the rocky bottom is characterised by a rich Fauna of those groups of
+animals, which, in the adult condition, are immoveably fixed. If a
+large stone or a water-logged piece of timber that has been at a depth
+of a few fathoms for some months or years be captured in the dredge and
+brought on board for examination, it is sure to present the observer
+with a multitude of firmly-fixed creatures. Among them there is almost
+certain to be found a number of small conical shells, made up of a
+series of triangular plates, fixed to the rock by their bases. These
+are commonly spoken of as Barnacles (_Balanus_), and they pass
+through an interesting history. For many years they were considered,
+from the character of their shells, to be allied to the Molluscs, but
+an examination of the soft parts of the animal shows that, unlike any
+Molluscs, they are provided with six pairs of jointed legs; and a still
+further study of their anatomy proves beyond a doubt that they can no
+longer be classified, with any pretence of scientific accuracy, with
+that group.
+
+                       [Illustration: +Fig. 11.+
+             Vertical section of a Balanus, showing animal
+                        _in situ_ in its shell.]
+
+The secret of their true relationship was not discovered until the
+story of the development was worked out, when it was found that the
+eggs they discharged each gave rise to a little larva called Nauplius,
+which is provided with three pairs of legs like the larvæ of some of
+the Prawns and their allies. The result of these observations then was
+to prove that the Barnacles are really Crustaceans, notwithstanding the
+fact that, unlike most of that group, they are, in the adult stage,
+permanently fixed to the rocks.
+
+On the same piece of stone there will most probably be found several
+twisted or coiled tubes of lime, formed by a little Sea-worm called
+Serpula. When living in the water the head of this worm projects from
+its shell and expands a circlet of delicate tentacles, by means of
+which the food is brought to the mouth. One of these tentacles is
+specially modified and enlarged at the extremity to form a conical
+knob, which, when the animal is retracted into the shell, closes the
+aperture like a stopper.
+
+                      [Illustration: +Fig. 12.+
+          Nauplius larva of a Balanus, enormously magnified.]
+
+Then there may be found some spherical or lobate masses of a fleshy
+consistency, white, pale pink or yellow in colour, and studded
+with numerous star-shaped apertures. When these are allowed to
+remain in a basin of fresh sea-water for some time, each one of
+the star-like apertures opens, and a beautiful transparent little
+Polyp with eight-feathered tentacles gradually unfolds itself, only
+to be slowly withdrawn into the mass when the vessel is shaken or
+otherwise disturbed. These Polyps form colonies, known as _Alcyonium
+digitatum_.
+
+Now it is to be noticed that none of these three examples of the
+sedentary Fauna can move in the least degree from the rock or shell
+to which they are fixed. When once the young larva has taken up its
+position there it must remain until old age or some disaster brings
+its life to an end. When they are first hatched from the egg that
+is thrust into the water by the parent, they pass through a larval
+stage that, like the Nauplius of the Barnacle, is active and free.
+Then they are carried away from the parent stock partly by their own
+active movements, but more particularly by the tides and currents of
+the sea-water. At last a change in their structure occurs. They sink
+to the bottom, become attached to a rock or stone, complete their
+metamorphosis, and remain anchored to the spot for the rest of their
+lives.
+
+The number of different forms of animal life which constitutes this
+sedentary Fauna of rocky coasts is very great indeed. In addition to
+the Barnacles, Worms and Alcyoniums, there are numerous species of
+Sea-anemones, Sponges, Corals, Zoophytes, Sea-squirts, and other forms,
+and in _all_ these cases the eggs give rise to free-swimming
+larvæ, by which the distribution of the species is effected.
+
+Another group of animals, which forms an important feature of some
+rocky coasts, are the Boring-molluscs. The Rock-borers belong to
+many different species. Some of them, such as the Pholases, make long
+cylindrical holes in chalk, and even in harder rocks. The Teredo is the
+borer, commonly known as the Ship-worm, on account of its powers of
+penetrating into timber. The long calcareous tube which it forms as it
+works its way into the wood, gives it a superficial resemblance to a
+large sedentary worm, but it is in reality a bivalve Mollusc, specially
+modified in structure for its peculiar habits.
+
+                      [Illustration: +Fig. 13.+
+                 Sea-urchin with large thick spines.]
+
+The next group of animals we have to consider in the Fauna of the rocks
+includes all those that slowly creep or crawl, without possessing
+any powers of rapid locomotion. Amongst these may be mentioned
+the Sea-urchins and Star-fishes. The former possess spherical or
+heart-shaped bodies covered with a formidable array of spines, among
+which there protrude several rows of soft transparent tubes terminating
+in little cup-like discs. Some of these tubes--or tube-feet as they are
+called--are fixed to a rock, and the heavy body is slowly dragged after
+them; another set is then attached, whilst the former is released to
+obtain another hold a little further on. The progress is slow, but the
+Urchin is able to climb the smooth face of an absolutely perpendicular
+rock with perfect ease or to get over any other obstacles that may be
+in its path. The Star-fishes are similarly provided with tube-feet,
+but in their case these are confined to the lower surface of the body,
+the upper side being entirely devoid of them. Star-fishes have a very
+wide distribution in the sea, and occur on sandy shores as well as
+among rocks and shingles. If a specimen be watched gliding slowly and
+smoothly over the sea-bottom and then the mouth be examined with a
+pocket lens, a doubt might arise in the mind of the young naturalist
+as to the justice of the charge that is made against these animals of
+their being the principal enemies of the hard-shelled Oysters. But the
+charge is well founded, for if a Star-fish be placed in an aquarium
+with an Oyster or a Cockle, or, in fact, almost any bivalve Mollusc,
+it may be seen to clasp its prey in its arms and slowly but firmly and
+surely force open the shells, and then protrude on to the soft parts
+a long tubular stomach which gradually digests and absorbs them. The
+Star-fishes, then, are undoubtedly to be reckoned among the most
+voracious and destructive inhabitants of the shallow waters, and it is
+probable that the covering of spines which we find so commonly among
+shallow water animals is an adaptation to prevent or render difficult
+the operations of these creatures.
+
+The Gastropod Molluscs form another large and important group of
+creeping animals of rocky coasts. On nearly all our own coasts numerous
+Periwinkles may be seen clinging to the rocks at low tides, and if a
+search be made in the deeper pools and on the rocks nearest to the
+low-water marks many other species will be found of animals with
+spirally-coiled shells which are included in this group of Gastropods.
+The Periwinkles on the rocks might at first sight be thought to
+belong to the sedentary group of animals, but when the water covers
+them again, or when they are put into an aquarium, they may be seen
+to protrude a head and an elongated slimy foot, which, gliding over
+the surface of the rock, drags the great shell and its contents with
+it. On the approach of danger the foot and head are withdrawn into
+the shell, and the animal rests secure from many enemies that might
+otherwise have found it a dainty morsel. Some of the Gastropods are
+purely vegetable-feeders, but most of those living in shallow sea-water
+feed upon Molluscs and other animals. It might well be a matter for
+wonderment when the soft head and little mouth of a Gastropod, such as
+a Whelk, are examined, that it is carnivorous and attacks and devours
+animals as large as itself. But the anatomist shows us that hidden in
+the recesses of that mouth there is a ribbon beset with numerous sharp
+little teeth, which by a complicated mechanism can be worked backwards
+and forwards in such a manner that it can bore a hole through very
+thick and dense shells; and, the soft parts being reached, a tube is
+protruded which dissolves and sucks them up into the animal’s stomach.
+
+Many people must have noticed that numbers of the bivalve shells
+that are cast up on the sand at low tide are perforated close to the
+hinge by a neat little round hole. This is the hole made by some
+predaceous Gastropod which, having killed its prey and devoured all
+that is digestible of it, leaves its empty shells at the mercy of the
+waves. Amongst the rocks numerous species of Gastropods are found,
+some undoubtedly carnivorous, others herbivorous. The many beautiful
+forms and colours that their shells assume may be seen in any good
+museum or conchological cabinet. Some of them are very minute, others
+are provided with a shell more than a foot in length; some are marked
+with numerous coloured spots, others with bands or lines; some have
+perfectly smooth shells, others are ribbed or spiny. It is extremely
+difficult to account for all these modifications, partly because it
+is impossible to study the animals alive in their natural habitats a
+few fathoms below the surface of the sea, and partly because life in
+the shallow waters must be so complicated that we are at a loss to
+understand the value to a species of slight modifications in structure
+such as these. The difficulty that has been found in explaining these
+various forms and colours has led some naturalists to the belief that
+they are of no importance to the species in the struggle for existence,
+that they are, as it were, the accidental result of some process of
+excretion, and not the outcome of a long series of slight changes,
+bringing about at length an adaptation of form most suitable to the
+habits of the animal. Such views are, however, to be accepted with
+great caution, and most zoologists will be contented to wait until our
+knowledge is much greater than it is at present, before wholly agreeing
+with them.
+
+                      [Illustration: +Fig. 14.+
+                      Smooth-shelled Gastropod.]
+
+                      [Illustration: +Fig. 15.+
+                           Spiny Gastropod.]
+
+Another great class of animals which has many representative forms
+among the rocks is the group of Crustaceans. The Lobster, the Prawn
+and the Crab are all familiar examples of this class. They may be
+found by searching rock pools at low-water, or can be captured in
+basket-work traps in places beyond low-water mark. When undisturbed
+they crawl slowly over the rocks and weeds by their long jointed
+legs, searching for their prey, but when alarmed the Lobster and
+the Prawn can, by violent flapping movements of their tails, dart
+rapidly backwards through the water, while the Crab beats a hasty
+retreat sideways into some shelter among the rocks. Like many of the
+Molluscs, the Crustaceans have a hard covering or shell to protect
+them from many of the dangers to which soft-bodied animals would
+be exposed, but a momentary glance at them would be sufficient to
+satisfy the most inexperienced eye that there are many and important
+differences in the character of the shells of these two great groups
+of animals. One important distinction between them, however, might
+well escape observation, and that is, that whilst in the Mollusc the
+shell increases gradually in size during the life of the animal, in
+the Crustaceans it cannot do so. In the Lobsters and Crabs the shell
+is periodically cast off entirely, and for a day or two at each period
+the skin of the animal is quite unprotected. A new shell is gradually
+formed, and this is hardened and thickened until it assumes a form
+similar to that of the one that has been lost, but larger. During the
+moult the Crustacean usually hides itself in a hole in the rocks and
+waits patiently until the new shell has grown.
+
+                      [Illustration: +Fig. 16.+
+                            A Cuttle-fish.]
+
+The animals included under the popular names of Cuttlefishes, Squids
+and Octopuses are also capable of crawling about among the rocks by
+their long feeler-like arms; but they are in the habit, as well, of
+making prolonged journeys through the water, by pumping the sea-water
+through a tubular siphon situated on the under side of their bodies.
+These animals possess in such a remarkable degree the power of changing
+colour that they might be called the Chamæleons of the sea. As they
+pass slowly through the water from one part of the coast to another
+the colour of the skin changes so as to resemble the colour of the
+rocks or weeds which are below them. These changes are brought about by
+numerous little bladders in the skin which are filled with different
+coloured fluids, and are worked by a complicated system of muscles
+under the control of special nerves from the brain. When the colour
+blue is predominant, it is found that all the bladders containing blue
+fluids are dilated, the others being constricted; when the colour is
+red the red bladders only are dilated, and so on; and as the nervous
+response to the colour of the rocks perceived by the eye is practically
+instantaneous, the change in the general colour of the body brought
+about by the dilatations of these vesicles is extremely rapid. Many
+other animals have the power of changing colour, but in no group is the
+alteration more rapid and remarkable than in this order of Cuttlefishes
+and Squids. Another very interesting feature presented by these animals
+is their ability to discharge suddenly a cloud of inky substance into
+the water. Their principal enemies are the Whales, Porpoises and some
+of the larger Sharks and other Fish. When these animals approach, or
+any other danger is feared, the Cuttlefishes discharge into the water
+from a special bag, called the ink-sac, a quantity of black or brown
+pigment which, diffusing rapidly, forms a cloud round their bodies, in
+the obscurity of which they frequently escape pursuit. The well-known
+Sepia of painters is obtained from these ink-sacs.
+
+The last group of animals occurring among the rocks are those capable
+of vigorous swimming movements. Many Crustaceans, such as the Lobsters
+and Prawns, are capable, as has just been pointed out, of swimming
+rapidly through the water by means of their powerful tails. But this
+swimming power is only accessory to that of crawling or creeping, and
+is used merely when the animals are disturbed. Cuttlefishes and their
+allies seem to spend a considerable portion of their time in floating
+or swimming in the water, but still they do crawl about among the
+rocks, and very probably attack and feed upon their prey entirely upon
+the sea-bottom.
+
+The members of the Rock-fauna which belong to the class of Fishes
+very rarely rest upon the sea-bottom at all. They are not, as a rule,
+provided with limbs which are capable of crawling or creeping; and
+their mouths are adapted for catching food that is swimming, or of
+browsing upon or nibbling at fixed forms of life while their bodies
+are still floating in the water. Nearly all the animals living among
+the rocks that we have hitherto spoken of, have some organs or some
+specialised portion of the body-wall for resting upon or for attaching
+themselves to the bottom.
+
+                      [Illustration: +Fig. 17.+
+                             The Wrasse.]
+
+The Anemones are attached by their bases; the Sea-urchins and
+Star-fishes crawl by means of their tube-feet; the Gastropod creeps
+over the rocks by its broad flat foot, and the Octopus stretches out
+its muscular arms and drags its body along by the numerous suckers they
+bear. In the Flat Fishes of the sandy and gravelly shores we usually
+find a white under surface on which they rest when waiting for their
+prey. Among the Fish which frequent the rocks, however, such as the
+Cods, the Whitings, and the Wrasse, there are no such surfaces. The
+body of the Fish is usually more rounded in form, and no well-marked
+limit can be assigned to the coloured upper surface and the pale
+silvery under side. These Fish are in nearly all cases rapid and
+powerful swimmers, rushing through the water after their prey, or away
+from their enemies, by vigorous lateral movements of their tails.
+
+A curious exception to this general rule among the Fish occurs in the
+family of the Lump-suckers. These Fish are found on the English, but
+more commonly on the Scottish coast, and are distinguished by the
+presence of a sucker, formed by the throat fins, on the under side of
+the head. By means of this the Lump-sucker is able to attach itself
+so firmly to rocks and stones that it can only with considerable
+difficulty be removed from the object to which it is attached.
+
+Of the Fish that are commonly found among the rocks, a very
+considerable number migrate from time to time to other parts of the
+sea, and may be caught in the trawl on sandy or shingly bottom, or even
+in the drift nets at the surface of the sea. A large number of Fish
+belonging to the family of the Codfishes frequent the rocks during a
+part of their lives. The Pollack is distinguished from most of the
+others by the absence of a barbel on the lower jaw, and is one of the
+persistent rock frequenters. In the adult condition it feeds almost
+entirely upon other Fish, although in the younger stages of its life
+Crustaceans, Worms, and other Invertebrates seem to form the bulk of
+its food.
+
+The true Cod and the Haddock seem to have a much wider range,
+occurring on shingly bottoms, where they are frequently caught in the
+fishermen’s trawls, as well as in the neighbourhood of rocks. The Hake
+feeds principally upon Pilchard, Herrings and Sprats near the surface
+of the sea.
+
+It is an interesting fact that the Fish belonging to this one family
+have very different methods of feeding. The Cod and the Pollack both
+hunt their prey principally by day-light. The Pollack is guided by
+its sight alone, the Cod-fish is assisted by its barbel, which acts
+as a delicate feeler or organ of touch. The Hake, on the other hand,
+retires into deep water during the day-time, and only comes to the
+surface at night to feed. Similarly the Rockling hides away in holes or
+under stones during the day-time, and only comes out to hunt for the
+Crustaceans and little Fish upon which it feeds at night.
+
+The development of these Fish presents some features of interest, as
+showing us the changes which occur in habit during their life-history.
+The eggs of the Cod are buoyant, rising to the surface of the sea as
+soon as they are spawned. In twelve or fourteen days, according to
+the temperature of the water, the larvæ are hatched and swim about in
+large numbers just below the surface, feeding upon minute Crustaceans
+and other animals. A little later the young Cod frequently shelter
+themselves under large Jelly-fishes, feeding upon the numerous
+parasites which infest those creatures. When they are about a year old
+they are found feeding among the sea-weeds on rocky coasts, and they
+migrate into deeper water when they reach their full size.
+
+                      [Illustration: +Fig. 18.+
+                            The John Dory.]
+
+The John Dory is a remarkable Fish, by no means confined to the rocks,
+as its food often consists largely of Pilchards and Herrings. It
+differs from most of the Fish of similar habits in being remarkably
+flattened from side to side. This feature seems to be of service to
+it in the peculiar manner it has of securing its prey. Mr Cunningham,
+to whom we are indebted for this interesting observation, says:--“It
+does not overtake (its prey) by superior speed like the mackerel, nor
+lie in wait for it like the angler, but stalks it and approaches it by
+stealth. It is able to do this in consequence of the extreme thinness
+of its body, and the peculiar movement of its hinder dorsal and ventral
+fins. The dory places itself end on towards the fish it desires to
+devour, and in this position it is evident that it excites no alarm on
+the part of its prey. The appearance of the dory seen in this way is
+a mere line in the water, to which no particular significance can be
+attached. I have not particularly noticed the effect of the ribbons of
+membrane, which project from the dorsal fin. But I have observed that
+the movements of the dory are very gradual except in turning; it alters
+the position of its body by a turn of the tail or side fins, and then
+slowly swims forward by vibrating the second dorsal and ventral, a
+movement which causes very slight disturbance of the water. The whole
+appearance of the dory in these actions is suggestive of suppressed
+excitement, his eyes being fixed on his prey.”
+
+                   *       *       *       *       *
+
+We have now considered some of the chief features of animal life in
+the shallow seas, the illustrations being taken principally from the
+regions of our home shores. The shallow waters of the tropics present
+us with so many phenomena of striking interest and importance, that
+the subject would be most incompletely treated if they were left out
+of consideration altogether, and, therefore, our next chapter will be
+devoted to them.
+
+
+
+
+                             CHAPTER III.
+
+                  SHALLOW WATER FAUNA OF THE TROPICS.
+
+
+The shallow waters of the Tropical seas present us with so many
+different conditions of tides, of coast lines, of temperature, of
+liability to storms, and of other natural phenomena, that we find an
+infinite variety in the general character of their Fauna. Just as on
+land, we find in one part of the Tropics a dense forest, and in another
+a dry desert, so in the Tropical seas we find on one coast a crowded
+population of animals and plants, and on another a sandy bottom, which
+is, comparatively speaking, lifeless. In order to bring before the
+reader some of the principal characters of animal life in the shallow
+waters of the Tropics it will be well to confine his attention to
+one part of the world which is fairly well-known--namely, the Malay
+Archipelago--and refer only in passing to other localities. The most
+characteristic feature of Tropical coasts is the Coral-reef, and
+nowhere in the world may it be seen in more exquisite variety than in
+the archipelagoes of the East. Although, however, these vast structures
+are so abundant on some coasts, others seem to be entirely without
+them. They are not found at all on the Western coasts of America or of
+Africa, and even in some regions of the larger islands in the Pacific
+and the Indian Oceans, many miles of coast line may be devoid of
+them. These curious and interesting variations in the distribution of
+the reefs can be explained, but the explanation will be more easily
+understood when their general features have been described.
+
+It is a well-known fact that the great masses of limestone which
+compose the reefs are formed by the activity of countless thousands
+of minute animals, but the popular idea of the general form of these
+animals has been very much misled by the unfortunate term “Coral
+insect,” which has crept into many books of travel, and the leading
+articles in the newspapers. The word “insect” is used by zoologists
+as a general term for certain air-breathing animals that are widely
+distributed over the surface of the earth. Many of them are extremely
+tiny, and hence the natural mistake has arisen in the untrained mind
+that all minute animals are insects. It might clear the ground a little
+if the reader would note at once that “insects” are very rarely indeed
+marine in habit. If there is a need for a popular word for the animals
+that form coral, it should be Coral “polyps” or Coral “anemones.” The
+word “coral” has, from the zoologist’s point of view, a very indefinite
+meaning, for it is applied to the hard skeleton of carbonate of lime
+formed by certain Sea-weeds, Sponges, and Worms, as well as to that of
+Coral-anemones and other Polyps. In many places on the British coasts
+the sea-bottom is very largely composed of a branching Coral formed
+by a true Sea-weed called _Lithothamnion_, and in other places
+very large lumps of rock are made by a Worm named _Filograna_. In
+the Tropical regions, too, the well-known Nullipores, which in many
+places play an important part in the formation of Coral-reefs, are of
+vegetable, and not animal origin.
+
+However, the greatest part of the Coral-reef is made by animals closely
+related to the Sea-anemones, living together in colonies; and of all
+the different kinds of Coral-polyps, by far the most prolific as a
+reef-builder is one which will be referred to in these pages as the
+Madrepore.
+
+                       [Illustration: +Fig. 19.+
+           Polyp of a Madrepore Coral, showing the canals by
+                which it is connected with its fellows.]
+
+Let us consider now the manner in which the Polyps form the Coral. In
+a very old work on the natural history of Corals a statement is made
+to the effect, that the Polyps construct the Coral in much the same
+way as Bees build their hive, or a Bird its nest. This very erroneous
+view coincides closely with ideas which might easily be gained by a
+casual observation of corals in a museum. The lime is not, however,
+collected as such from the sea by the Coral-polyps and plastered
+round their bodies to form a house or shelter, but it is formed as a
+secretion by the activity of certain organs of the animal’s body, and
+is consequently a true shell or skeleton. In a Coral, which is formed
+by a colony of numerous Polyps, the shell secreted by each individual
+fuses on to those formed by its neighbours, and thus a communal
+shell is formed which may assume a most complicated branching, bushy
+form, according to the species of the Coral and the conditions that
+are favourable or unfavourable to the nourishment and growth of the
+different parts of the colony. In such a Coral as the Madrepore every
+individual Polyp is connected with its neighbours by a system of
+branching canals; and as spaces are left for these when the shell is
+formed, the dried Coral is perforated by numerous tubular pores, and
+has a soft, spongy texture which can be easily crushed into a powder if
+trodden upon.
+
+In other Corals the canals of communication between the Polyps are
+entirely at the surface, and the shell that is formed is much harder
+and imperforate. In others again colonies are not formed, but each
+individual grows to a considerable size and remains independent of its
+fellows all its life.
+
+These, then, are three of the more important varieties of Corals found
+on the reef, the Perforate, the Imperforate, and the Solitary Corals;
+but it must be remembered that all the Corals of the reef cannot be
+included in these three groups. The varieties are much more numerous
+and in many cases much more complicated and difficult to understand.
+
+Although the Coral-reefs of the Tropical world have a general
+resemblance to one another, the differences in detail are so great that
+it is impossible to describe any one as typical. In sailing over the
+edge of a reef near the coast on a calm day, when the water is so clear
+that the bottom can be seen at a depth of 8 or 9 feet, the reef may,
+in some regions, be observed to change in character every few minutes.
+In one spot there may be clumps of living Corals surrounded by beds of
+fine white sand; in another there will be great stretches of branching
+Madrepores; in another Madrepores, Mushroom-corals, the Imperforate
+Brain-corals, Sponges, and many other forms of life will be clustered
+together; while further on the predominant features will be the soft
+and slimy Sarcophytums, looking like large green toad-stools, some
+lumps of Organ-pipe Corals and a few colonies of the Blue-coral.
+
+On other coasts I have wandered for miles along a reef mainly composed
+of endless tangles of Madrepores, with very little variation indeed in
+the general form of the Corals, in the character of the Sponges and
+Sea-weeds that grow with them, in their colour or in any other detail.
+Anyone reading the many accounts of Coral-reefs that have been written
+by travellers, must be struck with their inconsistency as regards
+many particulars; and in no one point are they more inconsistent than
+in the description of the colours--some writing in glowing terms of
+the beauties of the sea-gardens, and others complaining that their
+charms have been grossly exaggerated. As a matter of fact some reefs
+have a prevailing dull green or brown tone, while others exhibit all
+the colours of the rainbow in their more brilliant shades and tints.
+Another cause of the discrepancy is that some reefs can only rarely be
+approached in a small boat owing to the breakers that dash over them;
+whilst in the Tropical calms a tiny canoe can with perfect safety be
+manœuvred over the reefs during nine months of the year. From my own
+experience I can assert that it would be difficult indeed to exaggerate
+the glorious beauty of some of the reefs in the Malay Archipelago,
+more particularly of those where many different kinds of Corals may be
+seen in close proximity to one another. On such a reef, for example,
+there may be seen Madrepores with bright violet growing-points to their
+branches, orange or red Fan-corals, bright brick-red Sponges, yellow
+Sarcophytums, emerald green Organ-pipe Corals and dozens of other
+forms of animal life in every imaginable colour. When seen from a boat
+through two or three feet of water, these portions of the reef look
+more like a beautifully planted flower-bed than a mass of animals; but
+the simile is not a complete one, for the branches of the Madrepores,
+the great knobs and lumps of the Brain and Organ-pipe corals, the
+fronds of the Gorgonias and other forms make a wild mass of organisms
+resembling a tangled thicket or a miniature forest. At low-water of
+spring-tides the living reef is partly left exposed, and then the scene
+changes, for the Polyps retract their tentacles after the manner of the
+Sea-anemones and retreat as far as possible into the shelter afforded
+by their shells.
+
+                      [Illustration: +Fig. 20.+
+                              Chætodon.]
+
+The interest of the living reefs is, however, by no means confined to
+such organisms as the Corals and Sponges, which are immoveably fixed to
+the bottom; for numerous brightly-coloured Star-fishes, Sea-urchins,
+Brittle-stars, Sea-slugs, and their allies crawl about among the
+branches and the débris of the dead Corals; while Crabs, Lobsters and
+Shrimps of many kinds may be seen swimming or crawling in search of
+their prey, and the marvellously striped and spotted Coral fishes dart
+hither and thither in the thicket, or remain hovering in the water
+among the Corals. The whole scene is most fascinating. As the boat
+slowly drifts along, new and strange creatures are constantly coming
+into sight and disappearing again. Here the writhing arms of a bright
+blue Brittle-star may be seen embracing the stem of a Coral-branch;
+there a curiously flattened Chætodon, with its body marked by great
+diagonal yellow bands, is nibbling at the young, tender branchlets;
+in another place four or five Sea-urchins with very long and slender
+spines are lying apparently motionless on the bottom; while a little
+further on a long black Slug-like creature, the famous “Trepang” of
+commerce, is slowly wending its way across the reef. Now and again a
+large shoal of little Fish or a small party of Cuttlefishes may be
+seen, and these may rapidly be dispersed in all directions by the
+sudden dash of a Sea-perch or a small Shark. The interest is so varied,
+so many-sided, in these scenes of animal life that the attention of the
+naturalist is with difficulty kept to any particular point. The feature
+which is perhaps the most striking is, however, the wonderful variety
+in the colours of the animals and of the character of their markings.
+
+If we consider the Fishes alone, we find some of them have broad
+yellow bands running diagonally across their bodies, others have thin
+longitudinal stripes of blue and yellow, some have a uniform bright
+red colour, and others again have their red skins speckled with blue
+spots. It would take more than a whole chapter of this book to describe
+even the principal varieties of pattern found on one such Coral-reef,
+but the main fact that has to be related is that where the reefs are
+built by brightly-coloured Polyps, there we find these curiously marked
+Fishes. There can be little doubt that the marking and colouring does
+give a certain amount of protection to them. Numerous individual cases
+have been mentioned of Fishes which resemble some particular Sea-weed
+or Coral; but this general statement is the important one, that on
+a parti-coloured background the striped and speckled Fish are less
+conspicuous than those that are modestly attired.
+
+The Fishes of the reefs, however, have other means of protection than
+that afforded by their colours. The Trigger-fish and Coffer-fish, for
+instance, have a body encased in closely fitting hard, thick scales,
+so that they might almost be called “armour-plated fish”; and the
+Globe-fish bristle all over with long and extremely sharp spines. In
+the Trigger-fish there is a curious modification of the three front
+spines on the back, to which their name is due. It is not known
+precisely how they act, but they probably form an effective weapon of
+defence. In the same family of Fish we frequently find on each side of
+the tail two or three rows of sharp spines, which may also be regarded
+as defensive. In the family of the Surgeons there is only one of these
+spines on each side of the tail, and it is much larger than any of
+those in the Trigger-fish, and capable of being folded down into a
+case in the skin like a clasp-knife. It is said that these spines are
+connected with a poison-gland, and can give very severe and painful
+wounds, like the poison spines of our European Sting-rays and Weavers.
+
+                      [Illustration: +Fig. 21.+
+                             Globe-fish.]
+
+A few days’ hunting on a Coral-reef will reveal the fact that it
+supports a very considerable population of Crustaceans. They are not
+at all obvious at first to one who has had no previous experience of
+reef-work, partly because they resemble the general appearance of
+their surroundings very closely, and partly because of their habit
+of remaining perfectly motionless when first alarmed. In form, many
+of them are, like the Lobsters, Crabs and Prawns of our own coasts,
+but their colours and markings are, like those of the reef-fishes,
+characterised by their brilliancy and their arrangement in bands and
+stripes. The smaller ones can be caught after a little practice with
+a simple hand-net, but the larger ones are more easily captured by a
+rattan noose in the pools, after the blocks of Coral are loosened by a
+pick-axe and slowly turned over.
+
+The Coral-reef is a favourite hunting-ground for the conchologist,
+some of the largest and most beautiful shells in the world being found
+amongst the Corals. In Celebes, the giant bivalves, the huge Tridacnas,
+which are sometimes two feet across, and whose shells have been known
+to weigh as much as 500 lbs., may be seen wedged in among the Corals.
+The mantle of the living animal presents to the observer a wonderful
+display of colour as it lies in the shallow water with its shells open.
+The animal is eaten by the Malays, who roast it on a tripod spit over
+a fire, and cut it into steaks. A fair-sized Tridacna will afford a
+good meal for four or five men. The great Cowries, Helmet-shells, and
+many other species may be found in hunting over the reefs, but their
+beauties are frequently hidden, when alive, by the coal-black mantle
+which folds back over the shell as they crawl along. It must not be
+supposed, however, that all the shells of the reefs reach to such
+enormous size as those we have hitherto mentioned, for a rich harvest
+of species awaits the eager conchologist who hunts for the smallest
+shells he can find in the pools. Within the last few years a large
+number of new species of small Molluscs have been described from the
+coral seas, many of which do not attain to a total length of more than
+⅛ of an inch when perfectly adult, so that the range in size of this
+class of animals is very great indeed.
+
+So much has been said about the Madrepores, the Imperforate Corals and
+the solitary Corals of the reef, that the impression might be left
+that all the Polyps of the Tropics differ from those of the Temperate
+regions in the fact that they form shells or skeletal structures.
+This is by no means the case, for there are many species of true
+Sea-anemones and other Polyps to be found on Coral-reefs which make
+no shell at all, and others in which the body-wall is strengthened by
+numerous, but very minute spicules or grains of lime which, on the
+decomposition of the animal’s body, fall down into a shapeless powder
+or sand.
+
+True Sea-anemones are not very abundant on the reefs of North Celebes,
+but many species have been found on the Barrier-reef of the Australian
+coast, and among them specimens reaching the gigantic size of two
+feet in diameter--the largest size attained by single individuals of
+the class of animals to which the Anemones belong. Another family of
+Polyps called the Clavulariidæ belonging to the Alcyonarians has some
+species which make no skeleton of calcium carbonate. An illustration
+of one of these is given below (Fig. 22). Another species, called
+_Clavularia viridis_, which forms a few spicules in its body-wall,
+has a very wide distribution in the East Indies. In some places patches
+of it may be seen several square yards in extent, and the crowds of
+little Polyp heads with their eight-feathered tentacles waving to and
+fro with the pulsations of the tide, is a sight that excites immense
+interest and admiration in the mind of the observer.
+
+                      [Illustration: +Fig. 22.+
+                 Stereosoma, one of the Clavulariidæ.]
+
+One word more about the Corals. Where they are so abundant in number
+and species, where rocks hundreds of miles in extent are mainly
+composed of their shells and skeletons, it might be thought that a
+rich profit could be gained by collecting ship-loads of the Coral that
+is used for making beads and brooches by our jewellers. Any expedition,
+however, fitted out for this purpose would end in disastrous
+failure, for the Precious-coral is not known to occur anywhere in
+the neighbourhood of Coral-reefs, but the fishery is confined to
+certain parts of the Mediterranean Sea. Species closely allied to the
+Precious-coral, but of an inferior colour, have been found in the
+Japanese waters. None of the Coral structures found on the reefs have
+the same delicate salmon-pink colour and probably none of them are hard
+enough to take a good polish.
+
+The Coral-reefs which occur in different parts of the Tropical world
+were considered by Darwin under three heads,--Barrier-reefs, Atolls,
+and Fringing-reefs. The distinction between these three kinds of
+reef is not one that can be insisted upon scientifically, but the
+arrangement is convenient for purposes of description.
+
+The Barrier-reefs (Fig. 23, _B_) are situated at a distance of one
+to eight miles from the coast, and are separated from it by a lagoon
+of moderately deep water. The Barrier-reef of New Caledonia is said
+to be 400 miles in length and it follows the general contour of the
+coast line.
+
+The Atolls (Fig. 23, _C_) are ring-shaped islands composed of
+coral limestone with a lagoon of salt water within them, situated in
+the sea without any definite relation to other existing land.
+
+The Fringing or shore-reefs (Fig. 23, _A_) are situated at a
+distance of 100 yards or less from the beach and separated from it by
+a shallow lagoon which is frequently left as a dry sand-bank at low
+tides.
+
+                      [Illustration: +Fig. 23.+
+          _A_, Fringing-reef; _B_, Barrier-reef; _C_, Atoll.
+            _a_, sea; _b_, reef; _c_, rocks of the coast.]
+
+Many forms of reefs are found in different parts of the world, but
+they may all be looked upon as special modifications of one of these
+three groups. The facts which Darwin collected about Coral-reefs in
+his memorable voyage round the world in the _Beagle_, suggested
+to this great observer that all the different forms of reef must be
+related to one another, and he formulated an ingenious theory to show
+how, by the gradual sinking of the crust of the earth, Fringing-reefs
+may have become, in the course of a long period of time, either Atolls
+or Barrier-reefs. Some doubts have recently been expressed as to the
+truth of Darwin’s famous “subsidence theory.” But, whether it is true
+or not, to Darwin is due the credit of bringing home forcibly to our
+minds the fact that Coral-reefs are slowly undergoing changes of growth
+and of destruction, which must lead to most important and far-reaching
+alteration in the character of the Tropical seas. It is not intended
+in this work to enter into a discussion of the various alternative
+theories of Coral-reef formation, but a few words may be added on the
+method of formation of Coral limestone.
+
+In studying any one particular form of reef-building Coral we can find
+a long series of specimens from one inch in length up to a certain
+maximum, which varies with the species and the reef, but may reach
+over five feet in diameter as can be seen in the specimens now in the
+British Museum at South Kensington. Beyond this maximum size--let
+us say four feet in diameter--the Coral rarely grows, because at a
+certain age, probably when the vitality of the Coral is on the wane,
+the stalk of attachment becomes so bored with parasitic Sponges, Worms,
+Fungi and other organisms, that it is thoroughly rotten. If a large
+block be picked up from the reef, and with the help of two or three
+strong natives carried ashore and broken up with a hammer, a most
+interesting migration of Crabs, Worms and other creatures occurs, and
+the collecting bottles may be filled with a rich variety of animals
+parasitic on the Coral. Now the time comes when the stalk becomes so
+brittle that a heavy wave breaks it in two, and the Coral topples
+over and dies. If it falls into the sand, either on the inside or the
+outside of the reef and becomes buried, it may be preserved fairly
+complete, but if it lodges between other Corals the waves and the
+parasites between them dissolve it and break it up into thousands of
+pieces. This constant disintegration leads to the formation of great
+quantities of coralline sand which fills up the interstices between
+the living Corals, or gets washed over into the lagoon, or falls as a
+talus over the seaward slope of the reefs. In the latter case lumps of
+Coral torn off from the reef become embedded in it and form with it a
+bank which gives support to more living Polyps on the seaward slope.
+Consequently, in the course of many years, a reef which was at one
+time only fifty yards from the beach may have extended to a distance
+of a hundred yards or more, growing, as it were, on the skeletons or
+shells of the Corals that have died. There can be little doubt that
+Coral-reefs do grow seawards in this manner in some places, but they
+may also be either beaten back or kept for a long time perfectly
+stationary if the tides are too strong or too slack.
+
+What the precise conditions are which favour the growth seawards of
+Coral-reefs has not yet been systematically investigated; but we may
+suppose that if the tides are too strong the sand has no opportunity
+of settling between the Coral blocks and forming a solid limestone
+rock, and if they are too slow the Coral-polyps do not get sufficient
+nourishment to allow them to build fast enough to counteract the
+solvent action of the water.
+
+An interesting point connected with the Coral-reefs is the manner in
+which they are formed at first. A volcanic upheaval gives rise to a new
+island which, in the course of time, is surrounded by a Fringing-reef.
+How does this reef begin?
+
+The answer to this question has been recently given by the observation
+of the formation of new Corals on the shores of the island of Krakatoa
+which is situated in the Sunda straits, and was the seat in 1884 of
+one of the most violent volcanic eruptions of historical times. After
+the eruption the sea-bottom round the island was found to consist of a
+fine volcanic mud, in which it may be believed no Coral embryos could
+find a secure foothold. Now it is known that living Corals give rise to
+a number of very minute larvæ which for a period of time swim freely
+in the water, eventually settling down on some solid stone or shell
+to give rise by growth and budding to the Coral blocks. These larvæ
+frequently settle down on a piece of floating pumice-stone and after
+a time grow to such a size that they sink it. If, in sinking, they
+fall upon the bottom in shallow water they form together a substratum
+on which other larvæ can settle and flourish. This is apparently the
+manner in which Coral clumps are beginning on the slopes of Krakatoa
+and these will undoubtedly give rise in time to a more or less complete
+Fringing-reef.
+
+Any further discussion on this point would lead us into subjects
+beyond the scope of this book, but enough has been said to indicate
+to the reader the manner in which the countless Coral-polyps may, in
+the course of time, change the position of the reefs on Coral shores,
+thereby altering the set of the tides there, changing the position of
+the sand-banks, affecting the rate of erosion of the cliffs, and in
+other ways causing important modifications of the coast line.
+
+I have mentioned that the ground on the growing edge of the Coral-reef
+is carpeted with Corals, Sponges and many other forms of animal life;
+in the water swim countless Fish, and the branches of the Corals yield
+to the naturalist innumerable forms of creeping and crawling creatures.
+The shallow waters of the Tropics, as a whole, however, do not possess
+a particularly rich Fauna,--in fact, the distinguished Dr Kükenthal,
+who has had great experience of marine work, says that, in his opinion,
+the Tropical seas are not richer in littoral animals than the Arctic
+seas. Between the reef and the sea-beach there is a lagoon, of varying
+breadth, with a sandy bottom, which is almost as barren of animal life
+as a desert. A few Worms and Crabs, here and there a Star-fish and some
+shells of Foraminifers, are all the spoils which fall to the bag of
+the naturalist after many hours’ wading on this unprofitable ground.
+The reason for this is, perhaps, not far to seek. When the tide goes
+down many stretches of sand are left dry, and others retain only a
+few inches of water. The exposure to the heat of a Tropical sun soon
+kills and dries up any living animal that is unable to burrow deeply in
+the sand, and the water in the shallow pools rises in temperature to
+a degree that the human hand or foot can only just bear, so that the
+little Fish that escape into them run the risk of being slowly cooked
+alive.
+
+On the inside of the lagoon there is, in many places, a broad belt
+of Mangrove trees, forming the “Mangrove-swamp,” which contains
+some interesting and important animals. These trees have a peculiar
+spreading and branching system of roots which are left exposed when
+the tide goes down, and form with one another a kind of network or web
+a foot or more above the ground, upon which it is possible, with care,
+to walk from place to place, at low tide. Between the roots there is a
+slimy black sand or ooze, sometimes hard enough to walk upon, but more
+commonly soft and treacherous. At high tide the water rises to a height
+of two or three feet, completely covering the roots and giving the
+swamp the appearance of a forest growing in the sea. Of the animals,
+aërial and terrestrial, that haunt the swamps it is not necessary to
+say more than a few words, although they too form a study of great
+interest to the enthusiastic naturalist. But the marine zoologist who
+visits the swamps cannot fail to take note of the millions of Ants,
+Flies and Mosquitoes which torment him at every step, and make a
+prolonged stay an impossibility.
+
+                      [Illustration: +Fig. 24.+
+                           Periophthalmus.]
+
+One of the first creatures to be seen on entering a Mangrove-swamp
+at low tide is a curious little Fish called _Periophthalmus_.
+In some places hundreds may be seen at one time resting on the roots
+of the Mangroves, or skipping over the pools of water from one root
+to another. There are many varieties of _Periophthalmus_ in
+different parts of the world, and their habits are not exactly the
+same, so, to give an accurate description, our attention will be
+confined to the form occurring in N. Celebes. This little Fish is about
+three inches in length and remarkable for its very peculiar eyes, which
+are of a bright yellow colour, situated quite close together on the top
+of the head, and projecting so much from their sockets that the outline
+of more than two-thirds of the eye-ball can be seen. These eyes are
+extraordinarily moveable, and frequently revolve quite independently
+of one another, like the eyes of a Chamæleon, giving the animal a most
+grotesque and even ludicrous expression. These Fish seem to swim in
+the water very seldom; when undisturbed they may be seen clinging to
+rocks or trees by their fore-fins with their tails only in the water,
+but from time to time they spring into the air to catch a Fly on the
+wing, or a small Crab which has come unwarily within their range. Their
+fore-fins are peculiarly adapted to their habits, in that they have a
+very muscular base and a distinct elbow joint.
+
+These creatures are not easy to capture, as the ground on which they
+live is not adapted for rapid pursuit, and it is impossible to get
+close enough to them to catch them in a hand-net with a long handle.
+When kept in an aquarium it is seen that although they are rapid
+swimmers when they do go below the surface, they seem to prefer to
+live with their head and shoulders out of the water; and when chased
+in their natural haunts they very rarely, if ever, seek to escape by
+plunging into the water, but they execute a series of rapid jumps with
+extraordinary rapidity from root to root or rock to rock, and so avoid
+their pursuers. Their existence is really an amphibious one, and their
+food consists partly of Insects on the wing. Their gills are very much
+reduced in size, and it seems probable, from observations that have
+been recently made, that their respiration is partly carried on by the
+thin skin between the rays of the tail-fin.
+
+Another animal extremely abundant in the Mangrove-swamps of Celebes,
+and, like _Periophthalmus_, having a very wide distribution in
+similar places in other tropical countries, is the “Caller-crab”
+_Gelasimus_. These Crabs are about an inch in breadth across the
+back, and are remarkable for possessing one very much enlarged and
+brightly-coloured claw, the others being normal in size and dull in
+colour like the rest of the body. On first entering the swamp at low
+tide there may be seen on the mud between the roots of the trees a
+number of bright yellow, blue or green objects, which, as the traveller
+approaches, disappear one by one into holes in the ground. When the
+eyes are accustomed to the gloom of the swamp these bright objects are
+seen to be the great claws of the “Caller-crabs,” the rest of the body
+being inconspicuous owing to its close resemblance in colour to the
+slimy ground.
+
+These are the principal and most abundant marine inhabitants of the
+swamps, and as has been pointed out, all of them are more or less
+amphibious in habit. More locally distributed, Oysters and other
+bivalves may be found attached to the roots of the trees. Several
+species of marsh Gastropods occur, some of them in great abundance in a
+few localities. Occasionally a Sea-anemone, with remarkable powers of
+burrowing rapidly in the sand when disturbed, may be found, and to the
+microscopist a harvest of Foraminifers and other minute forms of life
+awaits investigation and description in the Mangrove-swamp.
+
+Whenever the tide is high a considerable number of Fish-fry,
+Jelly-fish, and other forms of floating and swimming life
+characteristic of these waters, drift into the swamps; and some being
+caught by the tangle of roots are left behind, either in the pools, or
+high and moderately dry upon the sand when the tide ebbs. Upon these
+victims of the retreating tide swarms of Ants and Flies descend from
+the trees, Crabs from the shore and from their holes in the sand are on
+the watch for them, Kingfishers and Sandpipers are ready to pounce upon
+those which are most to their taste, so that before the friendly waters
+of the ocean return to the swamp, scarcely one of them is left.
+
+These constitute what may be called in the swamp the _extraneous_
+Fauna, which if it is not truly indigenous is nevertheless necessary
+for the continued existence and well-being of the true inhabitants.
+
+The character of the sea-bottom on the outer side of the living
+Coral-reefs varies so much in different parts of the world that an
+adequate treatment of the Fauna in that region would have to be one of
+greater length than is possible in this book.
+
+The living edge of the Coral-reef is in some cases situated on the
+top of a submarine precipice of very considerable height, and in
+many places the sounding-line goes down to a depth of five or six
+hundred feet a few yards beyond the limits of the reef. The practical
+difficulties in the way of determining the character of the Fauna of
+any sea-bottom that shelves in this manner are very great, but where it
+is partly composed of massive lumps of solid Coral they are at present
+insurmountable. Every time the dredge or trawl reaches the bottom it
+becomes entangled in the Coral branches, and is liable to be seriously
+torn, or even lost. Swabs and iron hooks and fish traps may yield some
+scraps of information, but speaking generally, the Fauna of these steep
+slopes is scarcely known at all.
+
+The most important question, from the geological point of view, that
+has to be determined is the depth of water in which reef-building
+Corals can live and thrive. This is still a matter of uncertainty owing
+to the practical difficulties met with in the attempts to investigate
+it. Darwin estimated that the limit of vigorous coral growth was
+between 20 and 30 fathoms, but in recent years, owing to the discovery
+of luxurious Coral patches in 44 fathoms on the Tizard and Macclesfield
+banks, there is a pretty general opinion that his estimate is too low.
+
+Whatever the exact limit may be, it is quite clear that in many parts
+of the world the sea-bottom quite close to the outer edge of the
+reef cannot support a vigorous Coral fauna. Here and there patches
+of peculiar deep-sea species of Corals occur, but they do not form
+in such depths anything of the nature of a reef. They are usually
+isolated specimens, similar to those that are found in deep water on
+the Norwegian coast and other parts of the world outside the limits of
+the Tropics; but these specimens really belong to the deep-sea Fauna,
+of which we shall learn more in another chapter.
+
+In many places, however, the water at the base of the outer edge of
+the reef is not very deep, and may slope away gradually towards the
+bed of the ocean. The Fauna of such slopes in the Tropics is not
+characteristically rich, as my own experiences of dredging in such
+waters have proved. Time after time the dredge that was used in 15 to
+20 fathoms off the coast of Talisse, came up with nothing but sand
+or gravel. Occasionally a Brittle-star or a branch of dead Coral,
+with a few Zoophytes growing on it, came up; and in some places a
+few beautiful Lily-stars or Crinoids relieved the monotony of the
+investigation. But, on the whole, the animals found in this region were
+not numerous, nor of a character to excite any particular interest.
+
+Before bringing this chapter to a close, a brief reference must be made
+to one of the most remarkable phenomena in the animal kingdom,--this
+is the history of the Palolo worm. On certain parts of the coast of
+the Samoan islands the Palolo worm appears in great abundance in the
+early morning hours of one or two days at the beginning of the third
+quarter of the moon in the months of October and November. As the
+worm is regarded as a very great delicacy by the natives, the day of
+its appearance is looked upon as one of the most important red-letter
+days of the year. Weeks before the worms are expected the advent of
+the Palolo is discussed, stories are told of the fisheries of bye-gone
+years, anecdotes of the last year are remembered and rehearsed, and the
+whole population is prepared for the great event as for a feast.
+
+When the grand day arrives the boats are decorated, the girls put on
+all their finery, and everyone who can find a seat in a boat goes off
+to the fishery amid a merry chorus of song and laughter. It must,
+indeed, be a strange sight to see the flotilla of canoes with their
+eagerly expectant and gaily-bedecked crews, waiting in the dim light
+of the half moon for the day to break and the exciting fishery to
+begin. As soon as it is light enough to see into the water, a few
+writhing Worms may be distinguished at the surface, which increase in
+number with such extraordinary rapidity, that in a little while it is
+impossible to see anything below three or four inches owing to the
+multitude of Palolos. As quickly as possible the fishery proceeds,
+every man, woman, and child gathering the harvest of Worms during the
+precious moments of the sunrise. When at last the sun rises well above
+the horizon the Worm disappears again, and the boats hasten to the
+shores with their booty.
+
+This remarkable swarming process of the Palolo, occurring as it does,
+only once or twice a year, in constant relation with a particular
+phase of the moon, and lasting on each occasion only a few minutes in
+time, is not the only noteworthy feature of the animal.
+
+The Palolo worm, as it is caught, varies in length from an inch to a
+foot or more, and is about a quarter of an inch in breadth, but it
+readily breaks up into pieces when handled. It is composed of numerous
+rings or segments, each provided with a pair of processes bearing
+bristles, but there is no head. Astonishing as it may seem to those
+unacquainted with the natural history of Worms, it is nevertheless a
+fact that when the Palolo swarms it leaves its head behind among the
+Corals, where, in all probability, it regenerates a new body. This
+accounts for the fact that while the body of the Palolo is frequently
+brought home to our Museums in England, its head is a rarity. The
+colour of the Worm varies very considerably. The pieces bearing eggs
+are usually of some shade of green, hence the specific name _Palolo
+viridis_ that is given to it by scientists, but the males are
+usually white. In connection with the appearance of the Worm there is a
+curious statement that once in every four years it is exactly one lunar
+month late, so that the time of year of its occurrence is constant. The
+natives are also forewarned of the advent of the Palolo worm by the
+movements of the land Crabs, which, it is reported, come down from the
+fields and forest a few days before the Palolo feast and plunge into
+the sea.
+
+The precise habitat of the Worm when it is not swarming is still a
+matter of some doubt. A few rare specimens have been found in the
+Coral blocks in shallow water, but it is generally supposed that the
+majority of them live in deep water on the outer side of the reefs. It
+is not confined by any means to Samoa. It occurs also in Fiji, Tonga
+and other Pacific islands. A Worm similar to the Palolo in habits was
+described years ago by Rumphius in the Malay Archipelago, and Saville
+Kent mentions a little Nereid worm with similar spawning habits on the
+great Barrier-reef of Queensland.
+
+
+
+
+                              CHAPTER IV.
+
+                SURFACE-SWIMMING FAUNA (INVERTEBRATES).
+
+
+Everyone of an observant turn of mind must have noticed that in the
+wake of a boat that is passing through the water on a calm summer’s
+night, sparks of bright phosphorescent light may be seen to appear, to
+remain for a few seconds, and then become extinguished again. Sometimes
+the breaking of the ripples on the surface of the water seems to be
+sufficient to cause these sparks to appear, but occasionally streaks
+and flashes of pale blue light arise and disappear without apparently
+any such mechanical disturbance.
+
+The phosphorescence of the sea, as this phenomenon is called, is common
+enough on our coasts, but it never reaches the degree of brilliancy and
+beauty which is so remarkable in the open Atlantic Ocean, the South
+Seas, and some other parts of the world. In the Atlantic Ocean the
+phosphorescence is sometimes so bright that it is possible to read a
+book on deck by its light alone; and on a dark night in the Banda seas
+the water is often like a huge expanse of pale blue smoke studded with
+diamonds and other lustrous gems.
+
+These lights are mainly produced by animals which float and drift about
+on the surface of the water. It is not, as is very commonly supposed,
+only one or two different kinds of animals that are phosphorescent,
+but a vast number belonging to many widely different families and of a
+great variety of form and structure. When the day breaks many of these
+animals sink down a few fathoms into the darker and cooler strata of
+water, but a considerable number remain so close to the surface that
+they can be easily caught in a muslin net dragged after a boat.
+
+Some of these animals, such as the Jelly-fish, can, during the day, be
+observed clearly enough from the boat, others can only be seen when the
+contents of the net are emptied into a glass bottle, and others again
+are so minute that it requires a strong magnifying glass to detect them
+at all. Such animals that float or drift in the water without powers
+of swimming vigorously in one direction or the other, are collectively
+called the Plankton. In every sea, from the Arctic regions to the
+Equator, a Plankton will be found. Sometimes it is mainly composed
+of one species, in other cases it consists of many different species
+living together. Under certain conditions the water is simply crowded
+with these organisms, and in different circumstances the Plankton is
+represented by only a few individuals.
+
+The variations of the Plankton in different parts of the world have,
+of recent years, been subjected to many searching investigations, but
+although many important facts have been recorded, the explanation of
+the principal phenomena remains a mystery.
+
+One of the most interesting facts, perhaps, is the extraordinary
+local variations to be observed. To give a single example as an
+illustration of this point the case of the common white Jelly-fish may
+be mentioned. On occasions the surface of the water in our bays and
+estuaries contains so many of these animals, that the sea appears to be
+little more than a mass of jelly. In other seasons not more than a few
+isolated individuals will be seen all through the summer months.
+
+With all the resources of modern scientific investigation no adequate
+explanation has been given to account for this fact. It may be that the
+variation is due to the prevailing winds or tides, to the temperature
+of the water, to the roughness or smoothness of the sea, to disturbance
+of the ground where the eggs have settled, or to some other hitherto
+unforeseen conditions. Not only seasonal, however, but even diurnal
+variations occur, of a most remarkable and inexplicable character.
+
+On one occasion for example I was collecting a number of Jelly-fish in
+Southampton Water, and for nearly two hours specimens were obtained as
+fast as they could be hauled into the boat. Suddenly a change came,
+and in a few moments the water that had been alive with these animals
+seemed to contain not one. Another time, after dredging nearly all
+the afternoon at Lulworth for _Hormiphora_, with the very poor
+success of a half dozen specimens, the net came up simply choked full
+of these little round jelly-like Ctenophores, and for the remaining
+hours of day-light there appeared to be an abundance of them all along
+the coast. One morning in the Tropics, at about an hour after sunrise,
+I was looking over the side of a steam-boat, and saw that the surface
+waters were full of beautiful and rare species of floating animals. In
+less than half an hour afterwards, when a boat was put off, scarcely
+one of them could be found. Anybody who is accustomed to working with a
+tow-net can give similar experiences.
+
+In each of these cases a simple explanation might be suggested. In the
+first case it might have been the change in the tide which effected the
+disappearance of the Jelly-fish; in the second it might have been the
+approach of nightfall that caused the Hormiphoras to rise; and in the
+last case it might have been the approach of the heat of day; but when
+carefully considered such explanations are not sufficient, in that they
+do not account for the suddenness of the change.
+
+The fact is that the conditions of life in the surface waters are
+so complicated that it is extremely difficult for us to accurately
+estimate the balance of the forces which act upon these organisms. The
+direct heat of the sun, the light of both the sun and the moon, the
+tranquillity or roughness of the sea, the conditions of the tides and
+winds which cause changes in the surface temperature of the water,
+independently of the direct heat of the sun, all influence the delicate
+tissues of which these animals’ bodies are composed, and cause them to
+change their position.
+
+The animals which compose the surface Plankton may be considered under
+two heads--those that are adult, and those that are the larvæ of
+sessile and crawling forms of life which in the adult stage live at the
+bottom.
+
+Those belonging to the former group frequently occur far out in the
+open ocean as well as in the neighbourhood of the land, and have as a
+rule a wide geographical distribution. Those belonging to the latter
+group are more usually found within a few miles of the coast line,
+although winds and tides may occasionally drift them far out into the
+sea, where their larval existence is prolonged for an abnormally long
+time. Leaving out of consideration for the moment the many interesting
+exceptions, we may say that the Plankton of the open oceans differs
+from that of the neighbourhood of the coasts, by the larger proportion
+of adult forms that it bears.
+
+A great variety of animals pass the whole of their lives in the surface
+waters of the sea, but the commonest and most widely distributed of all
+probably are the Copepods belonging to the class _Crustacea_.
+
+The Copepods are minute creatures, rarely exceeding a quarter of an
+inch in length, which row themselves through the water by a pair of
+long antennæ, projecting from the head end of the body. They occur in
+fresh water as well as in the sea, and so abundant are they that if a
+glass tumbler be filled with the water from a pond, a lake, or the sea,
+and examined with a magnifying glass, a number of specimens are almost
+sure to be seen. They occur in abundance at the surface of the sea in
+nearly all climes, and very often are the sole representatives of the
+Plankton that are found in the hauls of the tow-net.
+
+Attention has already been called above to the fact that in the Tropics
+the surface-floating animals gradually sink down into the depths as
+the heat of the day approaches, but even on fine calm days a few
+Copepods will be found at the surface. Although they sometimes occur in
+Temperate seas in such vast numbers that the water is quite discoloured
+with them, more variety of form, or, in other words, more distinct
+genera and species are found in the warm and Tropical parts of the
+world.
+
+The study of this group reveals to the microscopist some of the most
+marvellously beautiful displays of colour and form that can be found
+in the animal kingdom. Sometimes the body and legs are beset with an
+immense number of extremely fine and delicate spines, which are in some
+cases provided with rows of still finer spinelets, giving them the
+appearance of a most minute feather. Sometimes the body contains large
+granules of a bright red colour, and at others smaller granules of a
+bright blue are seen scattered among the organs. The female Copepods
+usually carry, securely fastened to their tails, two little pear-shaped
+sacks of eggs, which are sometimes bright green, blue or red.
+
+                      [Illustration: +Fig. 25.+
+                       A free-swimming Copepod.]
+
+Endless are the varieties of form and colour presented by these little
+creatures, and endless are the beauties which the study of their
+structure reveals; but as we have mentioned them first as inhabitants
+of the surface waters of the seas, we must pause to consider here
+how these organisms, which excite so much wonder and admiration,
+are adapted or fitted for their peculiar mode of life. But it must
+be remarked that these statements apply only to the free-swimming
+Copepods, for many animals classed in this group by zoologists are
+parasites, and as such are so profoundly changed that they might at
+first sight be relegated to another class of organisms altogether.
+
+Now we must remember that animals that live in the surface waters must
+be prepared to keep afloat for the whole period of their lives--from
+the time they are hatched until they fall a prey to some voracious
+enemy. Under ordinary circumstances, they never find an opportunity of
+resting, either on the sea-bottom or on any floating substance.
+
+If a Copepod is watched in a tumbler of water it will be seen to give a
+number of strokes with its long antennæ and then to rest suspended for
+a few seconds; a few more strokes follow and then another pause, and so
+on. During the period of rest the body sinks slowly, sometimes almost
+imperceptibly, but never so much that it cannot recover its position in
+the water after the first few strokes.
+
+It must be clear to the reader that the less it sinks during the pause
+the less will be the muscular activity required to regain its position,
+and that, consequently, every mechanical contrivance that its body
+possesses to diminish its tendency to sink will be a saving of muscular
+and nervous energy.
+
+A very simple experiment will demonstrate that a body which presents a
+considerable surface to the water, sinks more slowly than one of the
+same weight that is round and compact. If we take two equal pieces of
+silver paper and roll one of them into a tight little ball, leaving
+the other as a flat sheet, and then let them sink together in a tall
+jar of water, the former will reach the bottom long before the latter.
+Similarly the body of an animal which possesses a dense armature of
+spines, as it presents more surface to the water, sinks much more
+slowly than the body of an animal of the same weight that is smooth and
+compact.
+
+The spininess or hairiness of the Copepod body, then, may be regarded
+as one of its adaptations to the environment in which it lives. But of
+course this character is not by any means confined to the Copepods.
+Very many of the surface-swimming Crustaceans, and more particularly
+their larvæ, have remarkably spiny bodies, and among many of the
+Foraminifers, Radiolarians, Worms, Molluscs and even Fish we find
+some similar extension of the surface of the body which lowers the
+sinking rate. Another means by which the bodies of many of the animals
+composing the Plankton are buoyed up, is the secretion into a special
+chamber or reservoir of some gas or oil of a lesser weight than the
+sea-water. This is what may be called the balloon principle. In such
+animals we may regard the heavy muscles, skeleton, skin and viscera
+as the car and the freight of the balloon, while the gas reservoir
+corresponds to the whole silk case containing the coal-gas.
+
+Such an animal might also be compared to a man in the sea clinging to
+an india-rubber life-belt. The body of the man by itself is heavier
+than the water, and in the absence of the muscular exercise of swimming
+sinks rapidly to the bottom; but the body of the man and the life-belt
+taken together are lighter than water and float continuously without
+any action of the muscles. If the life-belt were considerably smaller
+than usual the man and belt would sink, but much less rapidly than the
+man alone; and the muscular energy required to keep himself afloat
+would be far less with the belt than without it, consequently he
+would be able to keep afloat much longer with the same expenditure of
+muscular energy. The bodies of many of these surface-swimming animals
+may then be best compared with a man assisted by a _small_
+life-belt. When dead or still they slowly sink, but a slight amount
+of muscular energy expended in swimming is sufficient to keep them
+afloat. In what has been said above about the body of the Copepod,
+reference has been made to certain bright red granules. These are in
+all probability little globules of some oily or fatty substance lighter
+in weight than the sea-water, which serve to buoy up the body of the
+little creature. It is difficult to say why they should have such
+bright colours. We have no record of observations that show that the
+colours can be of any use to them as a protection from their enemies,
+nor is there any physical explanation of the colours of these granules
+any more than of the blood, the bile and other products of animal and
+vegetable vital processes. The eggs contained in the egg-sacks of the
+Copepods also bear a certain amount of oily substance very frequently
+different in colour from that of the other parts of the body, and this
+probably acts in the same manner upon the body of the parent or on
+that of the little larvæ when they are first hatched.
+
+Thus we find in the body of the Copepods at least two important
+modifications of structure, which render them fit or suitable for their
+life-long swim in the surface waters of the sea.
+
+Let us now consider another important group that has the same habit but
+differs from the Copepods in size and form, namely, the Jelly-fish.
+
+The Jelly-fish, or Medusæ, as they are usually called by zoologists,
+are disc or bell-shaped animals of a very soft gelatinous texture.
+From the centre of the disc or bell there hangs down a tube of varying
+length bearing the mouth, and the margin is often provided with a row
+of thin delicate tentacles like a fringe. (See Fig. 7). When watched
+on a calm summer’s evening they may be seen to slowly sink a few
+inches or more from the surface, and then with a series of convulsive
+contractions of the bell to rise to the surface again. Sometimes these
+contractions may be observed to continue perfectly rhythmically for a
+long time.
+
+In one of the commonest of the English Medusæ four rings of a bright
+pink or orange colour may be observed in the disc. These are eggs
+and male spawn, and when shed they give rise to multitudes of tiny
+little larvæ which sink to the bottom and become fixed to some rock
+or sea-weed. After the larva has securely fixed itself it becomes
+changed into a little Polyp which gives rise, in the course of time,
+to a number of small discs, arranged one above another like a pile of
+saucers. These discs break away from the base and from the parent stock
+to grow into the form and size of the adult Jelly-fish.
+
+We have here an example in the life-history of the common Jelly-fish,
+of what is known as “alternation of generations.” The eggs give rise to
+sessile Polyps, and these produce a number of buds which, when fully
+grown, give rise in their turn to the eggs; or, in other words, the
+egg-producing generation of large surface-swimming Jelly-fish regularly
+alternates with the small sedentary bud-producing generation. Now as
+the bud-producing or Polyp generation of the common Jelly-fish referred
+to is fixed to the bottom, the proximity to a coast, or at any rate
+to a shallow water area, is a necessity for the continuation of the
+species. Many of the Jelly-fish are undoubtedly drifted out into the
+open ocean by the tides, but the larvæ they produce, after swimming
+about in search of something solid to which they can attach themselves,
+must at last perish. It is only those larvæ which are hatched near
+enough to the shore to be able to reach the bottom during the tenure of
+their lives, that can continue the generation of these Jelly-fishes.
+
+But even in the open ocean far away from shallow water or a coast
+line, Jelly-fish, belonging of course to different species from those
+of the coasts, are found. What is their natural history? How is their
+life different from that of the Jelly-fish of the shore? Some of
+them produce larvæ very similar to those described above but they
+seek, instead of the rocks or sea-weed, other Jelly-fish and attach
+themselves to them as parasites.
+
+In other species, however, the “alternation of generations” is entirely
+lost, and the egg gives rise directly to a free-swimming little
+Jelly-fish which in time grows to be like its parent in size and shape.
+In this case the fixed or sessile form in the life-history is, as it
+were, omitted in order that the animal may lead a life independent of
+the coast and sea-bottom.
+
+The Jelly-fish, then, present us with an interesting example of a
+manner in which the life-history of an animal may be modified for or
+adapted to this surface-swimming habit.
+
+There is also another point of interest about these creatures in this
+connection. In writing about the Copepods I pointed out the mechanical
+contrivances they exhibit for keeping themselves afloat, namely, the
+spines, hairs and oil globules. Jelly-fish have neither spines nor oil
+globules of the same nature, but still their bodies are very light in
+the water and in the absence of muscular movements sink but slowly to
+the bottom. This lightness is due to the fact that all the tissues and
+organs of which it is composed are very largely distended with water.
+When the body of a Jelly-fish is analysed it is found that over 95 per
+cent. of it consists of water. This power of absorbing large quantities
+of fluid into the tissues, while it increases the size of the body,
+proportionately diminishes its weight in water.
+
+It has also another effect. It makes the tissues of the body much more
+transparent and gives them that soft jelly-like consistency which is
+so characteristic of the surface-swimming forms.
+
+The popular term ‘Jelly-fish’ is one that is frequently applied to
+many forms of surface-swimming animals that are really very different
+in structure and general composition from the true Medusæ. The Salps,
+for example, to which reference will be made presently, although soft
+and transparent in texture like the Medusæ, belong to a very widely
+separated group of animals, and to the anatomist it would be as absurd
+to classify them together, as to put the Butterflies and the Fish in
+the same group.
+
+These remarks are necessary because in the treatment adopted in this
+little book the animals that live together are considered in the same
+chapter, and it is important that the reader should bear in mind that
+they are not as a consequence anatomically related to one another.
+
+It is indeed remarkable that animals which are so different from one
+another, in their anatomy, development and life-history, as, for
+example, the Salps and the Medusæ, and which have had such a widely
+different ancestry, should, as a matter of fact, resemble one another
+so closely in form and texture as to be given collectively the same
+name by the unscientific observer.
+
+Among the heterogeneous crowd of animals that are popularly called
+Jelly-fish there is one particular group which presents us with some
+very interesting members. These are the Siphonophores. In many parts of
+the temperate and warmer seas of the world the surface may be covered
+with thousands of little creatures which, when brought upon the deck,
+seem to be little else than coloured bladders of air. The scientific
+name of these animals is _Physalia_. When placed in a glass of
+water, however, it will be seen that, from the under side of the
+bladder which floats freely on the water, numerous delicate tentacles
+and Polyps hang down. These creatures are kept at the surface by an
+air-bladder float and no muscular energy is required to sustain them in
+that position.
+
+                      [Illustration: +Fig. 26.+
+                     The swim-bladder of Velella.]
+
+Another Siphonophore called Velella has a bladder of a more complicated
+character in the shape of a disc with a semi-circular or triangular
+sail on its upper side. There can be no doubt of the advantage of
+this float to the species. It not only enables them to keep afloat
+without the expenditure of muscular energy, but as the wind catches
+the sail they are drifted along over great areas of the ocean and thus
+distributed far and wide from the spot on which they were hatched.
+Still the float has undoubtedly its disadvantages, for it exposes them
+to the danger of being blown ashore by a steady wind and so perishing
+in thousands. Agassiz says that on the coast of Florida the beach is
+sometimes marked with lines of Velellas that have been stranded in
+this manner, and I have seen in Celebes four or five rows of bright
+blue Physalias stretching for miles along the shore.
+
+In the Mediterranean and Eastern Atlantic Ocean a very large Physalia
+occurs which has received the popular name of the “Portuguese
+man-of-war,” and is famous for its stinging powers. The stinging
+is produced by a number of very minute sacs, which shoot out, when
+they are touched, a long pointed thread that penetrates the skin
+and conveys an irritant poison. These are called the thread-cells,
+and the “Portuguese man-of-war” is not by any means peculiar in
+possessing them. All the Medusæ and Siphonophores, all the true Corals
+and Sea-anemones have them--in fact, all those creatures which are
+classified together by the zoologist as _Cœlenterata_ may be said
+to be stinging animals. The thread-cells, however, vary very much in
+size in this group, and in the great majority of cases the thread is
+too feeble to perforate the skin of the human hand, and consequently
+their owners have not acquired a bad reputation.
+
+People do not warn their children not to touch the Sea-anemones on the
+rocks or the Jelly-fish stranded on the beach, and yet they are both
+dependent for their food upon their stinging powers; and indeed many of
+the British Medusæ which may be handled with impunity, are capable of
+stinging quite severely the more delicate skin of the back and arms of
+unwary bathers.
+
+Besides the two forms of Siphonophores which have been described,
+there are many others to be found at or near the surface of the seas
+of all climes. Some of them possess great floats like Physalia and
+Velella, but the majority of them have either no floats at all or such
+as are too small to do more than assist in keeping the animal near the
+surface. All of these Siphonophores are provided with little bells,
+which, contracting rhythmically like a Jelly-fish, drag the animal
+along, sometimes to the surface, sometimes a few fathoms below it.
+Some of these forms are extremely graceful, being like long strings of
+jelly, with numerous clusters of Polyps and long feathery tentacles,
+towed through the water by one or two exquisitely delicate little bells
+situated at the leading end of the string.
+
+A few words must now be said about the Salps, because in some seas
+the water is on occasions so full of them that they seem to be packed
+together ready for preserving. The simplest form of Salp is like a
+small sac or barrel of transparent gelatinous substance open at both
+ends. Running round the barrel are five or seven bands of a less
+transparent nature, appearing to the unaided vision like milky white
+streaks. These streaks are bands of muscles by which the movement
+of the body through the water is assisted. Sometimes they are seen
+swimming about independently of one another, sometimes Salps very
+similar to them in general appearance are seen to be attached to one
+another in long chains. At first it was supposed by naturalists that
+the former or Solitary Salps were of a different species to the latter,
+or Chain-salps as they are called; but it has been discovered that
+these two forms are but stages in the life-history of one species.
+When the anatomy of a Chain-salp is minutely examined it is found to
+contain a single egg, which gives rise to a young Salp similar in
+nearly all details to the solitary one. This escapes from its parent’s
+body when it is old enough to take care of itself, and leads an
+independent existence. After it has grown to its full size it gives
+rise to a stalk which divides up into a number of young Salps, attached
+to one another in a very characteristic manner.
+
+                      [Illustration: +Fig. 27.+
+     Solitary form of Salp, bearing a young stalk of Chain-salps.]
+
+Here, then, we have another instance of alternation of generations
+similar in this respect to the example previously quoted among the
+Jelly-fish, in that the one generation produces an egg, and the other
+numerous buds; but differing from it in the fact that in the case of
+the Salps both generations are adapted for freely swimming at the
+surface of the sea.
+
+Space does not allow us to say more in detail about the other animals
+of the Plankton that belong to the same group as the Salps; of the
+wonderfully interesting life-history of _Doliolum_; of the
+extraordinary bright light emitted by _Pyrosoma_, or of the
+remarkable little _Fritillaria_, shaped like a tad-pole, living
+in its house of jelly. The story of each of these might take a whole
+chapter to itself and still be only partly told.
+
+Anyone who is acquainted with the general appearance of the Whelks
+and Periwinkles, and other Gastropods of our shores might be well
+astonished when he saw, for the first time, many of the Gastropods of
+the high seas. The shell is either absent altogether or consists of a
+thin little papery cap far too small to afford protection to the body.
+The head and foot, and, indeed, the greater part of the body, are
+transparent, soft and gelatinous like a Jelly-fish, in fact the whole
+appearance is so different that it is not until the internal anatomy is
+carefully studied that their true position in the animal kingdom can be
+assigned to them.
+
+Here, then, we find another instance of a profound modification of
+structure associated with the surface-swimming habit; the modification
+being due very largely to the absorption of considerable quantities of
+water into the tissues of the body, which has the effect of rendering
+them transparent, and, at the same time, of reducing their weight in
+the water.
+
+The transparency of the body of so many of the animals of the Plankton
+has suggested the theory that by rendering them less conspicuous to
+their enemies it is of the nature of a protection to them. We ought to
+hesitate before accepting this theory until we know more accurately
+what are the enemies that they endeavour to protect themselves against.
+It is very probable that none of the Fish will feed upon any of the
+transparent Jelly-fish, neither is there any evidence that the Salps
+and the pelagic Gastropods form a favourite food for them. There is no
+good reason for supposing that the Sea-birds would, if they could see
+them better, prey upon them, so long as there are Fish in the sea to
+provide a more substantial and satisfactory meal. The Whales, as they
+dash through the water with their huge mouths wide open, undoubtedly
+swallow them in thousands, but it can not be reasonably supposed that
+the Whale can be guided by sight in the selection of its food. We ought
+not, perhaps, to go so far as to say that it is no protection to them,
+for Prof. Moseley states that the Turtle sometimes feeds upon the
+Velellas, but at the same time we may consider that the transparency
+is an effect produced by the large amount of water in their tissues,
+which is there for the purpose of reducing their specific gravity and
+assisting in that manner in their floatation.
+
+                      [Illustration: +Fig. 28.+
+                Pteropod, showing the so-called wings.]
+
+The only Gastropod found in the open seas which retains in its
+characteristic form the large coiled shell, is the beautiful blue
+_Janthina_, famous for its habit of constructing a little raft
+which floats on the surface of the sea. To the underside of this it
+attaches its eggs and spends its life in pushing or dragging the raft
+about.
+
+No account of the Molluscs of the Plankton would be complete without
+some reference to the Pteropods. These creatures are provided with a
+pair of muscular lobes of the body, which have been compared to wings.
+By means of these they are able to swim through the water. Some of them
+are provided with delicate little glassy shells, but in others the body
+is quite naked. We may regard the Pteropods as the most highly modified
+forms of Gastropods adapted for a pelagic life.
+
+In both the Arctic and Antarctic seas this group occurs in immense
+numbers, and it is supposed to form not an inconsiderable proportion of
+the food of the gigantic Right-whales. They also occur in the Temperate
+and Tropical zones, and indeed there are actually more genera and
+species there than in the colder regions to the North and South.
+
+The Insect world is represented at the surface of the ocean by a
+curious little Bug called _Halobates_. It is not uncommonly found
+in tropical or subtropical seas feeding upon dead Salps or Jelly-fish,
+and when disturbed scuds over the surface after the manner of many of
+the Insects living on our inland ponds and lakes. It has been described
+as an “ivory-legged fellow, covered with a bluish-white down.” As it is
+essentially an air-breather like all adult insects, its usual habitat
+is ‘_on_’ the sea and not _in_ it, so that strictly speaking
+it is not a member of the Plankton. There is no doubt that under
+certain circumstances it can and does dive into the water, and on these
+occasions it carries with it for respiratory purposes a layer of air
+attached to the ‘bluish-white down’ covering the body.
+
+There are no traces of wings on its thorax, and it is therefore
+incapable of flight. Very little is known at present of its
+development, and practically nothing of its internal anatomy, so that
+its proper position in the order of the Bugs or _Hemiptera_ is a
+matter of conjecture, but it is an interesting little creature, in the
+fact that it is the only member of its class that has a purely pelagic
+life-history.
+
+Among the microscopic forms of life found in the Plankton of the sea,
+the Radiolarians and Foraminifers are perhaps the most important. The
+Radiolarians are very minute specks of protoplasm, usually protected
+or supported by an elaborate skeleton of a substance closely allied
+to flint. The form of this skeleton varies so much in the numerous
+species that have been described, that it is quite impossible in a few
+words to give an adequate idea of the principal types. (See Fig. 2). We
+may say, however, that in a considerable number of them the skeleton
+has the form of a hollow sphere, perforated by numerous round holes
+and supporting outside a number of long thin needles. The anatomy of
+the Radiolarians is extremely simple. Their bodies are built entirely
+of protoplasm which performs all the vital functions. There is no
+definite head, mouth, brain, nor muscular organ. This being the case,
+the question arises, How do these animals provided with a skeleton
+of such a heavy substance as flint manage to support themselves in
+the water without muscular appendages? The answer to this question
+is two-fold--In the first place, the elaborate form of the skeleton
+presents an enormous surface to the water in proportion to its
+weight, and consequently sinks slowly; and secondly, the protoplasm
+is provided with numerous vacuoles containing a watery fluid, and in
+many cases at least one larger vacuole containing oil. If the liquids
+in these vacuoles are lighter than sea-water, and there is good reason
+to suppose that some at least of them are, then they are of the same
+nature as the oil chambers of the Copepods, and are hydrostatic in
+function.
+
+                      [Illustration: +Fig. 29.+
+       Shells of Foraminifers living at the bottom of the sea.]
+
+Among the Foraminifers very few genera strictly belong to the surface
+Fauna. Most of them have heavy, compact shells of carbonate of lime,
+and they live among the sand or the rocks at the bottom of the sea. The
+best known of the surface-dwelling forms is _Globigerina_, and
+this, in accordance with its habits, possesses a shell which, like that
+of the Radiolarians, is very light, perforated by numerous large holes
+and provided with long delicate spines. The shell of _Globigerina_
+might well be mistaken for that of a Radiolarian were it not for the
+fact that it is composed of carbonate of lime instead of flint.
+
+The Radiolarians in some waters, and the _Globigerinidæ_ in
+others, are present in enormous numbers, and as they die their shells
+fall in a gentle rain from the surface towards the sea-bottom, where
+they frequently, form a very large part of the abysmal mud.
+
+In speaking of the organisms of the surface of the sea no mention has
+yet been made of the plant world. Of the large conspicuous Sea-weeds
+that are often found far out in the open ocean the best known is the
+Sargasso or Gulf-weed of the Atlantic. It forms in some cases great
+floating patches, of very considerable area, and is, when alive,
+of a bright yellow colour. The Sargasso patches are, however, of
+great interest to the zoologist, because they support a considerable
+population of animals specially adapted by their form and colour to
+live among the Sea-weeds. They present us, in fact, with a peculiar
+Fauna, containing representatives of all the most important groups of
+marine animals.
+
+Besides the large conspicuous weeds like the Sargasso, the surface
+of the sea supports a large Flora of minute plants of very lowly
+organisation, and it is not at all uncommon for them to be present in
+such numbers as to cause a distinct discolouration of the water.
+
+                      [Illustration: +Fig. 30.+
+            Globigerina living at the surface of the sea.]
+
+The banks that they form on the coast of Brazil and elsewhere
+were called “Sea-sawdust” by Sir Joseph Banks. Moseley says that
+“when tracts of the sea are passed through, which are full of this
+_Trichodesmium_, the water lighted up by sunlight, when looked
+down into, appears as if full of small particles of mica or some such
+substance, so strongly is the light reflected from the minute bundles
+of the Algæ”; and again, he says, “so abundant is _Trichodesmium_
+in some seas that one of the explanations of the name of the Red Sea is
+that the term was derived from the discolouration of the water by vast
+quantities of _Trichodesmium erythræum_.”
+
+In addition to this “Sea-sawdust,” Diatoms, the still more minute
+organisms, the Bacteria, and the debateable particles called
+Coccospheres and Rhabdospheres, add to the number of the floating Flora
+of the seas.
+
+The importance of these organisms to the zoologist is that they must
+ultimately form the food supply of the animals of the Plankton. Some
+of the larger animals may feed upon the smaller ones, and the smaller
+ones may, in their turn, feed upon still smaller ones, but we must
+come eventually, in descending the scale, to the animals that are
+vegetable-feeders and prey upon the minute plants that have just been
+mentioned.
+
+Now that we have considered very briefly some of the principal forms of
+life that compose the floating and drifting population of the surface,
+we may return to the subject with which the chapter opened, namely, the
+phosphorescence of the sea.
+
+It need hardly be mentioned that it is a subject which is beset
+by innumerable difficulties. Even when the sea is extremely
+phosphorescent, and the observer is provided with an excellent
+microscope and all the necessary scientific appliances, he finds
+it difficult to answer the question--“What is the cause of the
+phosphorescence tonight?” The sample of water he takes may reveal to
+him a multitude of different organisms, many of which are so small that
+they can only be seen with a strong artificial light, and then it is
+impossible to say which are and which are not phosphorescent.
+
+Some of the Copepods are known to possess an organ emitting a blight
+blue star-like light which shines for a time and is then suddenly
+extinguished. In the Malay Archipelago several of these bright lights
+may be seen near the surface of the water on calm mornings just before
+sunrise, and it is extremely interesting to watch them gradually
+sinking down into deeper water as the day dawns, and then suddenly
+going out one after the other.
+
+Some of the large Jelly-fishes, such as _Pelagia noctiluca_,
+glow with a soft blue light. The curious pelagic Tunicate colony
+_Pyrosoma_ receives its name from the fact that it emits a bright
+light. A giant _Pyrosoma_ was caught by the _Challenger_
+in the deep-sea trawl, and, to quote the words of Professor Moseley
+once more, “It was like a great sac, with walls of jelly about an inch
+in thickness. It was four feet in length and ten inches in diameter.
+When a Pyrosoma is stimulated by having its surface touched, the
+phosphorescent light breaks out at first at the spot stimulated,
+and then spreads over the surface of the colony as the stimulus is
+transmitted to the surrounding animals. I wrote my name with my finger
+on the surface of the giant Pyrosoma as it lay in a tub at night, and
+the name came out in a few seconds in letters of fire.”
+
+All of these animals are sufficiently large to be easily seen by the
+naked eye, and the phenomena of their phosphorescence can be carefully
+observed. But many of the more minute forms of life also exhibit this
+peculiarity, and contribute in no small degree to the bright light of
+the sea.
+
+For instance, when the sea on our coasts shows a dull blue light,
+flashing into greater intensity where the ripples break, it will be
+found to contain immense numbers of very minute creatures called
+_Noctiluca_. Each of these has a gelatinous consistency, and is
+the shape of a microscopic cherry, bearing a short whip-like process,
+called the flagellum, which propels the organism slowly through the
+water. There seems to be no doubt that, on these occasions, the light
+is caused by these _Noctilucas_, but there are many other minute
+forms which abound on the surface and give off a pale phosphorescent
+light at night.
+
+We do not know for certain what may be the use of the phosphorescent
+light to the organisms that possess the power of emitting it. If we
+assume that the transparency of the bodies of the pelagic animals has
+a protective value in the day-light, it is difficult to understand why
+many of them should become so attractive, as the phosphorescent light
+makes them, at night. It is probable that the star-like lights of many
+of the Copepods may serve to attract to one another the two sexes, as
+it does with the Glow-worms and Fire-flies, but such an explanation as
+this cannot well be accepted in the case of _Pyrosoma_, which is
+hermaphrodite, or the _Noctilucas_, which live together in immense
+numbers. There can be little doubt, however, that there is some good
+reason for it, as it occurs in so many different animals belonging to
+widely separated families.
+
+In the neighbourhood of coasts or in shallow water, the surface of the
+sea usually supports a very large number of animals in a larval or
+immature state. These creatures live only a portion of their lives in
+a free-swimming condition, and then a change occurs during which they
+sink to the bottom and gradually assume the adult characters.
+
+Nearly everybody is acquainted with the general appearance of the Crab
+and Star-fish, but few would guess that the young stages of these
+animals are to be found among the minute transparent floating Fauna of
+the surface waters of the sea.
+
+The habits of the young and of the old, of these animals are widely
+different; the former must constantly support themselves in the water,
+they must feed upon and have means for catching and devouring minute
+floating organisms and must in other ways be adapted for life with the
+Plankton; the latter being unable to swim are capital crawlers and
+walkers over the rocks and sand of the bottom, have heavy bodies which
+sink rapidly in the water and, in other ways, are adapted for life with
+the shallow water Benthos.
+
+The conditions of life at the surface and at the bottom being, as
+I have previously pointed out, so different and the adaptations of
+structure to suit each set of conditions so great, we have, as a
+result, a long series of animals in which the young larval stages of
+life are absolutely unlike the adult and mature stages.
+
+No better examples to illustrate these changes could be given than
+those chosen from the group of the Echinoderms. Take, for instance,
+the common Star-fish with its thick heavy skin studded with plates
+of carbonate of lime, and its dense opaque body drawn out into five
+finger-like processes. These features of the animal indicate at once
+that its life is spent crawling on the sand or rocks at the bottom
+of the sea. If a Star-fish that has been caught in a lobster pot or
+brought to the surface attached to the bait on a fishing line, is
+cast into the sea it sinks to the bottom at once without any apparent
+effort to swim, to keep afloat, or to arrest its rapid descent. It is
+therefore clearly unfitted for a surface-swimming existence, but its
+eggs give rise to larvæ which are admirably adapted to it, and can
+indeed only exist at or near the surface of the sea. These larvæ are,
+as a rule, when first hatched, covered with a number of very minute
+vibratile cilia, by means of which they swim with considerable rapidity
+through the water. After a time a number of bands appear, which are
+covered by specially long cilia and then the smaller cilia on the
+intervals between the bands disappear.
+
+                      [Illustration: +Fig. 31.+
+ Young larva of a star-fish before the Brachiolaria stage is reached.]
+
+The precise arrangement of the bands differs in the different species,
+but from being at first perfectly circular in contour they become more
+and more curved and twisted, sometimes fusing with one another and in
+parts degenerating, until, at last, when the larval stage reaches its
+full development, the bands have assumed an elaborate and somewhat
+fantastic pattern.
+
+The body of the larva is, like that of so many surface-swimming
+creatures, extremely transparent. The uniform oval shape which it
+has when first hatched becomes changed as it develops by the formation
+of a certain number of short blunt processes or arms, and it was the
+presence of these which caused the older naturalists to call this larva
+the Brachiolaria.
+
+If one of these minute Brachiolaria larvæ be caught and examined with a
+microscope it is not difficult to see that it has a little round mouth
+leading into a short digestive canal which opens to the exterior by a
+vent. It is therefore clearly capable of feeding itself and leading
+a perfectly independent existence. In the older larvæ there will be
+noticed an appearance which has, under a low magnifying power, the form
+of an incomplete and rather opaque ring round the stomach. This opaque
+ring becomes larger and larger, it exhibits five projections radiating
+from its centre, and at last gives rise to all the organs of the fully
+formed Star-fish. As the ring develops the larva sinks from the surface
+and loses the power of independent feeding, and then, when all is
+ready, the skin is cast off and a small but perfectly formed Star-fish
+emerges.
+
+The Trepangs, the Brittle-stars, the Sea-urchins and other Echinoderms
+have, as a general rule, life-histories similar to that of the
+Star-fish, but there is one point of difference in detail which is of
+sufficient interest to be mentioned before passing on. The larva of
+the Brittle-stars and of some of the Sea-urchins has a number of arms
+which are much longer, in proportion to the whole size of the larva,
+than they are in the Brachiolaria, and on account of the manner in
+which these arms are inclined towards the apex, the larva has a rough
+resemblance to the form of a painter’s easel. This type of larva is
+called the Pluteus. The main point of interest about the Pluteus,
+however, is that the arms are supported by delicate bars of carbonate
+of lime which are connected together at the apex and form a very
+definite larval skeleton.
+
+                      [Illustration: +Fig. 32.+
+                            Pluteus larva.]
+
+This larval skeleton is cast off with the skin when the metamorphosis
+takes place, and it is consequently of great interest to scientists in
+the fact that it is one of those structures which are formed to meet
+the exigencies of larval life only, and is perfectly useless for the
+adult. In considering the manifold questions which arise in the study
+of the relation of animals to their surroundings we are often inclined
+to fix our attention too exclusively upon the adaptations that are
+manifested in the adult form. In the case of some classes in which the
+immature stages of life are passed through very rapidly and under the
+protection of the parents, this is not to be deprecated; but in most
+cases it is important to remember that in the struggle for existence
+there is such danger of extermination that each stage of life may have
+acquired special characters for adaptation to its particular mode of
+existence. The peculiar markings and colours of the Caterpillars is
+a familiar example of the special characters of larval forms among
+terrestrial and air-breathing animals, but in none of these do we find
+so great a specialisation in larval characters as in some of the marine
+forms of life.
+
+It is said above that the Echinoderms as a general rule have
+free-swimming larvæ, but there are exceptional cases which have an
+interest for us quite as great as that of the ordinary life-history.
+
+Many Echinoderms are found living in very great depths of the ocean
+and it is difficult for us to believe that any of these can have
+pelagic larvæ similar to those of their shallow water relatives. The
+difference in pressure between that of the bottom of the deep-sea and
+of the surface is, by itself, sufficient to convince us that a delicate
+organism like a Brachiolaria or Pluteus could not make the upward
+journey unharmed; but when we add to that the great distance of two or
+even three miles in a direct line, the difference in temperature and in
+light, we must realise that the ordinary transformations of the shallow
+water Echinoderms is an impossibility for the deep-sea varieties.
+
+As a matter of fact we know very little about the life-history of
+deep-sea Echinoderms, and this is not a matter for wonder when the
+reader reflects upon the great difficulties that have to be overcome
+in obtaining a few specimens of the adult forms; but at least one of
+the Star-fish of the Abyss has been found to bear little pouches or
+pits in which the young are fostered until they are ready to lead an
+independent life in the form of the parents.
+
+It has also been shown that in some of the Arctic Star-fishes the
+larval life is in a similar manner abbreviated and protected, and
+it seems probable that this may be accounted for by the fact that
+the surface waters, where the larval forms would live if they were
+liberated, are for very long periods covered with ice.
+
+The great group of the Crustaceans also presents us with many
+interesting larval forms specially adapted to surface life. In a
+previous chapter I have pointed out that the Barnacles of our coast
+give birth to curious little free-swimming, six-legged larvæ called
+Nauplii, which after having undergone two or three further changes,
+settle down on a rock and assume the adult features (see Fig. 12).
+
+It is not known how long these changes take in the ordinary course
+of nature, but it is quite probable that the larval life is a
+comparatively short one.
+
+Some Barnacles, however, live far out at sea on drifting wood or
+parasitic on the skin of Whales, and it is reasonable to suppose that
+when their larvæ are hatched a very considerable time may elapse before
+they find a suitable resting-place to complete their metamorphosis.
+
+The life-histories of these species are not at present accurately
+known, but a few remarkable Nauplii have been found which, there is
+reason to believe, are really the Nauplii of some kind of Barnacle and
+are specially adapted to a long life at the surface by the enormous
+length of their spines.
+
+In the specimen discovered by Chun in the Canary Islands, of which
+a figure is given here, the spines were seven or eight times the
+length of the body, the eye was remarkably small, and the muscles were
+feebly developed. It may be that this is the larva of some species of
+Barnacle, which, from the character of the host or home where it lives
+when adult, must be prepared to wait a long time in its larval habitat
+before the chance comes for it to find a suitable resting-place.
+
+                      [Illustration: +Fig. 33.+
+                    Long-spined Barnacle-nauplius.]
+
+Many of the Crabs and Prawns have remarkable larvæ, characterised
+either by two or three extremely long spines or in some cases by a
+festoon of shorter and many branched spinous processes spreading out
+from their carapace, tail and limbs. These spines may be regarded
+partly as a device for assisting in the floatation of the body,
+and partly, perhaps, as a protection against some of the creatures
+that feed upon them; but in both respects they are special larval
+adaptations to the pelagic life. It is extremely interesting to find
+that in this class of animals the same characters are not constant
+in the larvæ. A Prawn called _Palinurus_ has a larva the body
+of which becomes extremely expanded and flattened, so as to resemble
+a very thin sheet of glass, the eyes and the limbs at the same
+time undergoing remarkable modifications. Another larva becomes
+extraordinarily distended by the absorption of water into its tissues
+so as to resemble in texture a small Jelly-fish.
+
+A great deal more might be said about the story of Crustacean larvæ,
+as it is one which is full of interest and wonder, but throughout the
+whole of it we see, wherever there is a larval history at all, that
+some one or more of those characteristic features have been evolved,
+which were previously noted in adult animals as an adaptation to their
+free-swimming pelagic life.
+
+In many other groups of marine animals we find the same alternation of
+a transparent larval life at the surface and an opaque adult life at
+the bottom.
+
+The Oysters, Clams and Mussels, the Winkles and other Gastropods, the
+Worms, the Sponges and many other forms of life that creep among the
+Sea-weeds and are fixed upon the rocks or burrow in the sand, produce
+exquisite and delicate transparent little larvæ which for a certain
+length of time at least float and drift about in the light of the
+sunshine in the surface water. They have, of course, many varieties of
+form and many peculiar organs for locomotion and floatation, so that it
+is possible for a competent zoologist to tell without much difficulty
+the group of animals, if not the actual genus and species, to which any
+particular larva belongs.
+
+It might be thought that, as so many of the animals living near the
+coast line in shallow water have pelagic larvæ, the Plankton of the
+neighbourhood of the coasts would differ from that of the open oceans
+in the fact that a considerable proportion of it consists of these
+larval forms. But many of the larvæ seem to be able to live a long time
+without further change than an increase in size, and being drifted out
+to sea by the winds and tides are often found in the open ocean at very
+great distances from any coast line.
+
+It would be interesting to know more of these larvæ which go thus
+astray. How long can they go on waiting for the opportunity to cast off
+their childish clothes and assume the garments of the adult? Do they in
+time undergo changes which bring about a kind of childish old age, or
+do they suddenly perish with all the characters of youth upon them?
+
+These and many other questions connected with this most fascinating
+chapter in the story of the sea have still to be answered by the
+investigations of scientific men in the future.
+
+
+
+
+                              CHAPTER V.
+
+                 SURFACE-SWIMMING FAUNA (VERTEBRATES).
+
+
+In the preceding chapter we have considered only those animals of
+the surface of the sea, which, owing either to their small size or
+the transparency of their bodies, are not as a rule conspicuous to a
+passenger on board a mail-steamer. Such a passenger might cross the
+ocean many times without realising in the least the wealth of animal
+life that there is in every wave that breaks upon the ship, and yet
+be impressed with what he has seen of the Whales and Porpoises, the
+Sharks, Bonitos and Flying-fish.
+
+It is to these groups of animals that a few lines must be devoted
+before closing our story of the surface-swimming Fauna. If the young
+and immature stages be for the moment left out of consideration, it may
+be said that nearly all the Fish and all the Whales and Porpoises are
+large, opaque in appearance, and perfectly conspicuous. Moreover, they
+are all strong and rapid swimmers, capable of roaming over wide areas
+of the sea in search of prey, and independent of, except in so far
+as their prey are influenced by, the currents and winds. It is clear
+that they cannot be said to ‘float’ and ‘drift’ about in the ocean,
+and consequently they do not strictly belong to the Plankton. The term
+used in speaking of them collectively is the Nekton, which means the
+swimming population.
+
+The greatest number of the Fish of the sea are shore Fish; that is to
+say, they habitually feed at, or close to, the bottom of the shallow
+waters near the coasts or sunken banks.
+
+But there is a very considerable number that are strictly pelagic,
+living and feeding far away from the shores, bringing forth their young
+alive, or shedding floating eggs, and in every way independent of the
+shore and of the bottom.
+
+It is difficult to give any general features by which they are
+characterised, as so much variety may be observed among them; but as
+a general rule they are elongated in form, round or oval in section,
+in colour green or gray above, with silvery white bellies. Some of
+these, such as the Flying-fish and the Flying-gurnard, are capable of
+making very considerable flights in the air, their pectoral fins being
+enormously elongated, and when fully expanded somewhat similar to the
+wing of an Insect.
+
+The Flying-fish occur in shoals in nearly all tropical and subtropical
+seas. When disturbed by a ship on a calm day it is said that they
+spring out of the sea, expand their fins, describe a regular parabolic
+curve in the air, and then fall with a splash into the water. There is
+a considerable controversy raging on the question of the use of their
+fins in this flight through the air, some observers believing that
+the fins are used only as a kind of parachute, and others that they
+are used like wings for raising the body above the water. It is very
+difficult to decide which view is correct.
+
+In the Indian Ocean I watched the Flying-fish for several days during
+rather rough weather, and my impression was most distinctly that in
+the middle of the flight the fins are vigorously flapped four or five
+times, the flapping being followed by a decided rise in the air. On the
+other hand, it may be that this flapping appearance is caused by the
+wind catching the wings in a certain position, and not by the muscles
+of the fish. Whether the flying is actually assisted by the flapping
+of the wings or not, it is certain that the Fish do rise in gusty
+weather to a very considerable height, frequently falling on to the
+decks of steamers twenty feet above the water line.
+
+At night, these Fish fly at the ships and not away from them, as
+they do in the day-time, and the natives in some parts of the Malay
+Archipelago catch them in large numbers by holding up a torch by the
+side of a large sheet, when the Fish flying at the bright light and
+striking against it, fall into the bottom of the canoe. Flying-fish are
+excellent to eat, their flesh being similar in taste to that of the
+Herring, but an epicure would probably say that it is not quite so good.
+
+The Bonito is a fish occurring over a wide area of the tropical and
+temperate seas, which sometimes makes tremendous jumps out of the
+water. I have seen it frequently on the coast of Celebes jump to a
+height which I roughly estimated as at least fifteen feet. It is said
+to feed upon the Flying-fish, and it is probable that it has acquired
+the power of springing out of the water in the pursuit of its prey.
+
+The pelagic Fish, which has acquired the widest reputation, and that
+an evil one, is the “blue-Shark.” This occurs in the tropical and
+occasionally in temperate seas. Its usual size is from twelve to
+fifteen feet, but, according to Dr Günther, individuals of twenty-five
+and more feet are occasionally captured. It is extremely voracious,
+attacking anything of a fleshy nature that it observes in the water.
+
+One of the most remarkable animals of the open ocean is the Sun-fish.
+It has a very wide distribution in the tropical and temperate
+regions. In the adult condition it is almost circular in outline and
+considerably flattened from side to side like a John Dory. It sometimes
+reaches a size of eight feet in diameter and a very great weight. From
+the little that is known of its development it apparently undergoes
+some extraordinary changes in shape before it reaches the adult form.
+
+                      [Illustration: +Fig. 34.+
+                            The Sun-fish.]
+
+In addition to these and several other Fish of a large size which may
+be found at the surface of the open ocean, there are several species
+known to science which never grow to a length of more than a few
+inches. Many of these are characterised by remarkably long fin rays,
+by their large eyes, or by other features which may be regarded as
+special modifications for their peculiar habits.
+
+A very interesting genus is _Scopelus_, which is found very widely
+distributed in tropical and other seas. Some of the species live in
+very deep water, and are purely abysmal in habit, but most of them rise
+to the surface at night, when they may be caught in immense numbers.
+In form they are not unlike a small Sprat, but they exhibit on each
+side of the body a series of minute eye-like organs, which emit a
+phosphorescent light.
+
+In addition to these Fish which are found far out in the open ocean,
+there are several genera, which form an important feature of the
+surface waters in the neighbourhood of the coasts. Among them we
+find such valuable food-fish as the Herrings, Sprats, Mackerels, and
+Pilchards.
+
+The complete history of the Herring has yet to be written, for,
+notwithstanding the laborious investigations of several naturalists,
+working independently, or as officers of the Marine Biological
+Association and similar Institutions, there are some facts and stages
+which have, up to the present time, escaped observation.
+
+The Herring species is divided into a number of races, which, differing
+from one another only slightly in anatomical characters, have different
+seasons for depositing their eggs. This fact has only recently been
+thoroughly established; and while it assists us greatly in the task
+of completing the history of the Fish, it definitely destroys the
+validity of many theories which were prevalent among fishermen and
+others before the days of the more exact scientific treatment of
+fishery questions.
+
+It is well-known that from the end of the month of June to December
+immense shoals of Herrings are found in the North Sea. It is quite
+impossible to estimate the numbers of Fish in these shoals, but they
+are so great that if they could be counted it would probably be found
+that the Fish that are annually caught by all the fishing boats, form
+but an insignificant fraction of the whole. All of these Fish are in
+such a condition that it is evident their spawning time is close at
+hand. When they are ready they approach the coasts, the exact time
+varying according to the race of Herrings, and the spawn is deposited
+on or close to the ground, the eggs becoming attached to stones and
+other objects on the bottom. After the Herrings have spawned, they seem
+to disperse, or, at any rate, to disappear from the surface waters of
+the North Sea. What actually becomes of these shoals of spent Herrings
+is not known, but it is a fact that in the spring there are so few
+Herrings to be found in the narrower part of the North Sea that it does
+not pay the fishing boats to go after them. It is possible, however,
+that, after the spawning process, the Herrings migrate to the deeper
+water of the Norwegian coasts, in order to feed on the Crustaceans and
+other forms of life that are to be found there in abundance.
+
+The Mackerel do not apparently make such extensive migrations as the
+Herrings. They spawn in the open sea, five or ten miles from the
+coast, during the spring time. The egg of the Mackerel, unlike that of
+the Herring, does not sink to the bottom when it is spawned, but, being
+provided with a large oil globule, it is light enough to remain on the
+surface until the young larva is hatched. After the spawning has taken
+place the Mackerel approach the coast, and will even enter bays and
+narrow inlets on the shores in pursuit of the young Sprats and other
+small Fish upon which they prey.
+
+A great deal could be written on the history of the Pilchards, the
+Anchovies, the Sprats, and other Fish which frequent the surface waters
+of the sea in the neighbourhood of the European coasts. No two species
+seem to have precisely the same habits, and what is known about them
+presents us with many curious and remarkably interesting facts. For
+further details, however, I must refer the reader to the larger and
+more comprehensive books dealing specially with the subject, for space
+must still be found for a few words on another group of animals which
+play a conspicuous part in the story of life in the seas.
+
+The animals composing the class of Mammals are distinguished from other
+Vertebrates by the fact that the females are capable of providing milk
+for their young ones after birth. Most of the Mammals are strictly
+terrestrial, but three orders, namely, the _Cetacea_, the _Sirenia_,
+and the _Carnivora_ contribute to the surface-swimming population of
+the sea.
+
+The _Cetacea_ are all aquatic. The order includes the many genera
+of Whales, Porpoises and Dolphins.
+
+The Right-whales are distinguished by the enormous size of the mouth
+and the absence of the little triangular fin in the middle of the back
+which is found in the other Whales.
+
+These animals have no teeth in the adult condition, but are provided
+with a series of plates situated at the sides of the mouth which are
+used as strainers to catch the small Pteropods and other animals
+living in the water which pass through the great gape. The plates are
+composed of a substance called “Baleen,”--the well-known whale-bone
+of commerce,--they are triangular in shape, and frayed out into a
+brush-like edge on the side that faces the cavity of the mouth. The
+Greenland Right-whale attains to a size of fifty feet in length when
+fully grown, and it is usually found in shoals among the ice floes of
+the far north.
+
+In former times many Right-whales belonging to species allied to
+the Arctic form occurred in the temperate regions of the Atlantic
+and Pacific Oceans, but in consequence of the valuable fishery they
+afforded they are now becoming very scarce.
+
+The largest of all the Whales--in fact, the largest existing animal--is
+the Blue-whale, which attains to the enormous length of 86 feet. It
+spends the winter in the open seas, and approaches the coast of Norway
+in the spring.
+
+The Whales, like all the animals of the Class to which they belong,
+are air-breathers. They are able, however, to hold their breath for a
+considerable time under water. When they come to the surface to renew
+the air-supply in their lungs, they first make a violent expiratory
+effort from the nostril, and drive a column of spray many feet into
+the air above them. This phenomenon is called by the whale fishers
+“spouting,” and it was erroneously supposed by them to be a column of
+water forced from the mouth into the nostril, and then expelled at the
+surface.
+
+The Dolphins and the Porpoises are distinguished from the true Whales
+by the fact that they are provided with teeth, on one or both of their
+jaws, and there is no “whale-bone.”
+
+The Sperm-whale has probably been called a “Whale” from its enormous
+size, but it is anatomically very widely separated from the true whales
+and more closely allied to the Dolphins. It has no “whale-bone,” and
+the lower jaw is provided with a row of sharp-pointed teeth set in a
+groove in the bone. Its great value is due to the fact that there is
+a large cavity situated above the skull, containing an oily substance
+from which “Spermaceti” is made.
+
+The principal food of these large “Toothed-whales” seems to be
+Cuttlefishes, and the examination of the contents of their stomachs,
+which has been carried out on board the Prince of Monaco’s private
+steam-ship when engaged on a scientific cruise, has yielded some new
+forms of these giant Molluscs. The Sperm-whales, however, do not
+disdain a Fish diet as well.
+
+The Porpoises are found on our own coasts. They may often be seen
+following the “schools” of Whales as they approach the coast in the
+summer months, and they occasionally chase their prey some distance up
+the estuaries of the English rivers. The habit that Porpoises have of
+accompanying ships for long distances affords us many opportunities
+of watching their graceful movements, and of estimating the very
+great speed with which they can swim through the water for hours at a
+stretch. It is difficult to understand the meaning of this habit of
+following ships. It has been suggested that the Porpoises mistake the
+ship for a huge Sperm-whale, and hope to benefit by stray morsels of
+large fish that fall from its jaws. But this theory does not account
+for the fact that the Porpoises so often go in front of the ship. The
+following extract from Darwin’s “Voyage of the Beagle” gives, in a few
+words, a vivid picture of Porpoise life:--
+
+“In our passage to the Plata, we saw nothing in particular, excepting
+on one day a great shoal of Porpoises, many hundreds in number. The
+whole sea was in places furrowed by them; and a most extraordinary
+spectacle was presented, as hundreds, proceeding together by jumps,
+in which their whole bodies were exposed, thus cut the water. When
+the ship was running nine knots an hour, these animals could cross
+and recross the bows with the greatest ease, and then dash away right
+ahead.” This description reminds me very forcibly of a sight I once saw
+in the Talaut Islands, south of the Philippines. In passing between two
+of the islands the strait seemed to be alive with Porpoises tearing
+through the water at a terrific pace. They accompanied the steamer for
+about six hours and then suddenly disappeared. My impression was that
+they were attracted to the ship not from a desire for more food, for
+there was an abundance of Herrings in the straits at the time, but from
+sheer curiosity. I think the feeling of curiosity, that is to say, the
+desire to go and look at something strange or unusual, is much more
+prevalent among animals than we generally suspect.
+
+                      [Illustration: +Fig. 35.+
+                         The common Porpoise.]
+
+It is an interesting fact about the Porpoise that, although it is so
+fish-like in shape, it should present some features which remind us of
+the Pig. The English word is probably derived from the two French words
+_porc_ and _poisson_, and therefore means “Pig-fish.” The
+Germans call it Meeresschwein, meaning “Sea-pig,” and the Malay word
+for it is “Babi-laut,” which also means “Sea-pig.” But if we make some
+allowance for those who call these Cetaceans “Pigs,” we must make none
+for those who call them “Fish.”
+
+Like all the other members of their order the Porpoises have a
+fish-like tail, but the flaps are placed horizontally and not
+vertically as they are in Fish. The skin is quite naked, having no
+scales of any kind, and there are no gills or gill-openings. Like
+all other Mammals the Cetaceans bring forth their young alive, suckle
+them, and breathe air by means of lungs. But there can be no doubt that
+they are extremely modified for their aquatic life. The characteristic
+covering of Mammals--the hairs--is, in the adult condition of the
+Whales, entirely wanting, and is represented in other members of
+the Class by only a few bristles on the snout. The heat of the body
+is maintained by a thick coat of fat, called the blubber, lying
+immediately beneath the skin, and this yields, on boiling, a valuable
+oil, which helps to support the whale-fishermen. One of the most
+striking modifications, however, is the loss of the hind limbs. It is
+only in some species that even rudiments of these have been found. All
+of these facts indicate that the Cetaceans must have taken to a mode
+of life in the water a very long time ago, and the study of the rocks
+proves the existence of Whales as far back as Eocene times, but it is
+of interest to note that, in some respects, the oldest fossil Cetaceans
+are less specialised than those that are now living.
+
+The class of Mammals called the _Carnivora_ includes the Cats,
+Dogs, Ferrets and many other animals which are purely terrestrial,
+but one of its divisions is entirely composed of those well-known
+aquatic animals the Seals and the Walrus. If we take the common Seal
+as an example of this group, and compare it with the Porpoise, as a
+representative of the Cetaceans, we find that in habits as well as in
+anatomy the former is less completely changed than the latter. The Seal
+frequently comes to land to bask in the sun, or to produce and care
+for its young, and it is capable of making some progress over the rocks
+by the help of its flipper-like fore-limbs; the Porpoise, on the other
+hand, never leaves the water of its own free will. Unlike the Porpoise
+the body of the Seal is covered with a thick coat of hairs, and the
+hind limbs are retained. Although there is a general resemblance in
+the form of the body between these two animals--this form being, in
+all probability, mechanically the best for rapid progress through
+the water--a glance at their skeletons shows great and important
+differences, which the merest tyro in anatomy could point out. In
+expression, too, there is a marked difference, for while the Porpoise
+has a certain cast of countenance which, when seen at a distance,
+deserves the epithet “pig-faced,” the face of the Seal, with its large
+round eyes, its small nose and high intelligent brow, is almost human
+in expression.
+
+The Seal has a habit of raising its head above the water and staring
+at an approaching boat, and when doing this it may readily be mistaken
+at first sight for a man overboard, but no one could ever mistake a
+Porpoise for a human being.
+
+The common Seal has a very wide range occurring near the coast of
+both the Atlantic and Pacific Oceans. It is found on some of the more
+sequestered parts of the British shores, but not in large numbers,
+for the common Seal, unlike many of its allies, does not appear to
+congregate in large shoals at any time of the year. They are described
+as being timid, inoffensive creatures, easily tamed, passionately fond
+of their children and taking an intelligent interest in music.
+
+There are several animals closely related to the Seal, occurring
+in different parts of the world; and a few words may be said about
+the remarkable animal called the “Sea-elephant,” which is found on
+Kerguelen island in the Antarctic Ocean. The popular name was given
+to the animal in consequence of the fleshy protuberant nose which has
+been compared with the trunk of an Elephant and is possessed only by
+the male. The late Professor Moseley, who came across a small herd of
+them when the _Challenger_ was at Kerguelen, says: “The trunk is
+produced by an inflation of a loose tubular sac of skin placed above
+the nostrils, just as is the ‘Cap’ in the northern Bladder-nose Seal.
+The trunk is evidently, as appears from both the drawings, sacculated,
+and hence irregular in form when inflated.”
+
+The Sea-lions and Sea-bears or the Eared Seals, as they are sometimes
+called, form a very distinct family. The one that is best known to
+the general public is the Californian Sea-lion, as it often lives in
+captivity in the European menageries for many years and attracts the
+attention of the visitors by the tricks which it is taught to perform.
+
+In the spring months of the year these creatures may be seen in great
+numbers on the rocky islands off the coast of California, where they
+come to breed.
+
+The most important of them all, from a commercial point of view, is
+the Fur-seal from the Northern Pacific. In the month of May these
+animals approach the Prybilov islands in the East, or the Commander
+islands in the West of the Behring Sea. The first to arrive on the land
+are the old males. These choose for themselves certain areas or ‘homes’
+on the shore and fight desperately for their possession with all who
+dare to come within their reach. When matters are at length somewhat
+settled the time arrives for the females to approach the shore.
+The fighting then begins again with renewed vigour, and desperate
+encounters take place for the possession of a goodly stock of wives for
+the season.
+
+There seems to be little in the way of courtship in the domestic
+economy of the Fur-seals, the wives being simply “captured” by the
+scruff of their necks when they come within reach of a would be
+husband, and retained in his harem just so long as he can prevent
+any one of his neighbours from stealing her. The Fur-seal, like all
+his relations, is polygamous, but the number of wives that each male
+appropriates to himself seems to vary very considerably. Mr Elliott
+mentions a case in which there were as many as forty-five females in
+one home, but, as a general rule, the number is much less. As there is
+only one male to every twelve or thirteen females, there are numerous
+males over, which cannot found a home for themselves. These bachelors,
+together with a number of the young females, resort to a separate
+piece of ground, where they spend their time in playing games. The
+play-grounds are however the scene of the tragedies of Seal life, for
+they are resorted to by the hunters, who slaughter immense numbers of
+the larger males for the sake of their valuable skins. As the skins of
+the old male Seals are not of very much value and as it is important,
+for the perpetuation of the race, to preserve the females from injury,
+the breeding grounds are usually not molested. It is therefore the
+bachelor seal of from two to five or six years of age that has to
+supply the market. Those naturalists who have visited the Seal
+rookeries on these islands say that the numbers of these animals that
+can be seen at one time is almost incredible. We can form some estimate
+of them when we learn that over a hundred thousand skins are exported
+from the Prybilov islands alone every year.
+
+The Seals leave the rookeries in the month of August, and after
+swimming about for some time in the neighbourhood of the islands,
+eventually depart into the open ocean in search of the food their
+famished bodies need so much after the fasting and fighting of the
+breeding months.
+
+The largest of all these aquatic Carnivores is the Walrus, which lives
+within a short distance of the shores of the lands in the Arctic
+regions. It is easily distinguished from the Seals by its great size,
+the males reaching a length of 10 or 12 feet, and by the enormous
+canine teeth in the upper jaws, which project downwards from the cover
+of the lips in the form of two large pointed tusks. These tusks are
+used for hoisting the bodies of the animals on to the ice, for digging
+in the sand in search of the Mussels upon which they feed, and for
+general fighting purposes.
+
+It is said that in former times the Walruses lived in immense herds
+in regions much further south than they do now; but the ravages of
+the hunter, who chased them for their ivory tusks and their oil, have
+driven them into regions where they are rarely visited by anyone but
+the Arctic explorer; and to those of my readers who wish to learn more
+of their habits, I can but say that in the pages of Dr Nansen’s book,
+“Farthest North,” he will find the story of the Walrus written in a
+manner which no man living could have done more vividly and brilliantly
+than the great Norwegian zoologist and explorer.
+
+
+
+
+                              CHAPTER VI.
+
+                            DEEP-SEA FAUNA.
+
+
+Some of the most important conditions under which life at the bottom
+of the deep-sea occurs have been mentioned in the first chapter. We
+have pointed out that the pressure is enormous, that the temperature
+is only a few degrees above the freezing point, and that, except in
+those places where phosphorescent animals emit a faint light, it is
+absolutely dark, no rays of direct sunlight being able to penetrate
+such a mass of water as lies between the bottom of the ocean and its
+surface.
+
+With such conditions to contend with it is not surprising that the
+naturalists at the beginning of the century believed that no animals
+could possibly live on the floor of the great oceans. Their beliefs,
+however, merely afford us an example of the danger of prophesying
+without knowing, for the great expeditions which have investigated
+the ocean-bed during the last thirty years have proved the existence
+of a rich and peculiar Fauna in all the great depths that have been
+dredged. The general results of these investigations have been recently
+summed up by Dr John Murray in the last volume of the _Challenger_
+Reports. He points out the extraordinary variety of life in the deep
+sea as shown by the contents of the dredge. “At Station 146 in the
+Southern Ocean, at a depth of 1375 fathoms, the 200 specimens captured
+belonged to 59 genera and 78 species.” He can find no record of species
+equal to this in depths of under 50 fathoms, and concludes that the
+evidence at present before us is sufficient to warrant the belief that
+the great depths of the ocean are as a general rule extremely rich in
+species.
+
+From what has been already said, it may be gathered that nearly all
+the most important groups of marine animals have representatives
+in the deep-sea. There are Fish, Tunicates, Crustaceans, Molluscs,
+Echinoderms, Worms, Cœlenterates and Protozoa. Nearly all of these are
+so modified, either in form or colour, or the structure of their organs
+of sense, or in other particulars, that they could be recognised at
+once in a collection as deep-sea animals; but there is a small minority
+which seem to have undergone but little change in adapting themselves
+to their strange environment.
+
+We may commence our study of this remarkable Fauna by a few remarks on
+their colour. The first and most striking feature is that the animals
+are almost invariably uniform in colour. If they are dark-brown they
+are dark-brown all over, if they are red they rarely exhibit bands of
+white or spots of blue. Moreover, they are not always in harmony with
+the colour of their surroundings.
+
+In the shallow waters the animals that live among the green Sea-weeds
+are green, those that live on the sand are coloured like the sand, and
+many of those that live among the rocks are darkly pigmented with black
+and blue. In the abyss of the ocean, where there is any light at all,
+the colour is, in all probability, fairly uniform over wide tracts, and
+yet we may find in one haul of the dredge, black Fish, red Crustaceans,
+and purple Trepangs.
+
+There seems to be no particularly predominant colour among the deep-sea
+animals. Most of the Fish are black or dark-brown, but many are light
+violet, some are pale rose and others bright red. Among the Crustaceans
+bright red seems to be the prevailing shade, just as the darker tints
+of black and brown are among the Fish.
+
+Among the Echinoderms we find white, purple, yellow, red, and pink
+forms, and among the Jelly-fish and Corals, red, violet, and green. In
+fact it would be necessary to describe every class of animals in turn,
+and then almost every genus in each class, to give an adequate idea of
+the variety of colour met with in the Fauna of the deep-sea.
+
+It is inconceivable that each of these animals can live amid
+surroundings of a colour similar to its own, and therefore we may
+without much hesitation believe, that the colour of deep-sea animals is
+not, as a general rule, of use as a protection.
+
+Next to the peculiarities of colour, the most striking features of
+the more highly organised inhabitants of the bottom of the sea are
+the modifications of the organs of special sense. The Fish, the
+Crustaceans and the Molluscs almost invariably exhibit some remarkable
+modifications of the eyes. In their natural haunts there must be
+either absolute darkness, or the faint and usually intermittent light
+emitted by phosphorescent animals. How intense this light may be it
+is impossible to judge. The light that is emitted by animals on the
+deck of a ship can afford no criterion of the light they emit under
+a pressure of two tons to the square inch. However, the fact that
+the deep-sea animals have either very large eyes or no eyes at all,
+suggests forcibly that this light is not sufficient to cause a general
+illumination.
+
+Some of the Fish are quite blind, and although most of these have a
+very small and rudimentary eye, in at least one Fish, _Ipnops_,
+which is peculiar to deep water, no trace of an eye is to be found.
+
+In some genera with a very wide distribution, a very interesting series
+of stages may be found, indicating the changes that may have taken
+place in the history of the blind Fish of the abyss. In the genus of
+deep-sea Cods (_Macrurus_) for example, those species which live
+in water of less than a thousand fathoms depth have very large eyes,
+and those that are found in greater depths have much smaller ones.
+
+The same in general is true of the Crustaceans. The deep-sea Cray-fish
+have lost not only their eyes, but also the stalks which supported
+them. In _Bathynomus_ (a Crustacean belonging to the group
+_Isopoda_), however, there is a pair of enormous eyes. But as a
+rule the eyes of Crustaceans degenerate and disappear in shallower
+water than the eyes of Fishes. At depths of 500 fathoms or greater,
+the eyes of the Crustaceans usually show signs of reduction in size or
+other retrogressive changes, and in the greatest depths they are nearly
+always wanting altogether.
+
+                      [Illustration: +Fig. 36.+
+             A deep-sea Fish showing very elongated fins.]
+
+Accompanying the loss of eyesight in deep-sea animals we often find
+a very remarkable development of organs, which may be regarded as
+especially tactile in function.
+
+Many of the deep-sea Fish, for example, with rudimentary eyes possess
+long barbels, and in some cases the paired fins are enormously
+elongated to form delicate pointed organs like the tentacles of a
+Polyp. Among the blind Crustaceans, too, we often find enormously long
+antennæ, and even the claws and legs are so long and delicate that they
+bring to mind the appendages of a Daddy-long-legs or a Harvest spider.
+
+Just as a blind man acquires a remarkably acute sense of touch, so, it
+seems, in the course of generations, these blind animals of the abyss
+have acquired extremely delicate tactile organs.
+
+The deep-sea Fauna is also remarkable for the great number of animals
+which are phosphorescent. As in the surface-swimming creatures the
+phosphorescence is not confined to a few classes, but probably occurs
+to a greater or less extent in all the more important groups. The word
+“probably” must be used in the previous sentence, because it is not
+yet scientifically proved that many forms which are supposed to be
+phosphorescent are actually so; but the evidence is conclusive that
+phosphorescence is a common and widespread character of most of the
+deep-sea Fauna.
+
+The Fish exhibit, perhaps more than any other group, peculiar organs
+which are supposed, and in many cases proved to be, used for the
+purpose of generating light. In the _Stomiatidæ_, a family of Fish
+related to the Salmons, there are often numerous little organs, like
+minute bull’s-eye lanterns, arranged in rows on the sides of the body
+from the head to the tail, and in addition to these in some species one
+or more pairs of larger organs are seen on the upper lip just in front
+of or below the large eyes. It is not certain what the colour of the
+light is that is emitted by these organs, but it is very probable that
+if the Fish could be seen in their natural haunts they would have an
+extremely beautiful effect.
+
+In describing the general characters of the shallow water Fauna in
+Chapter II. reference has been made to the remarkable lure at the end
+of the tentacle of the Angler-fish. In the Angler of the great depths
+this is also found, but in the obscurity of their surroundings a lure,
+such as that of the shore species, would be useless, and it is actually
+replaced by an organ which is supposed to be phosphorescent. The mouth
+is enormous and armed with ferocious-looking teeth, the body is rounded
+and adapted for burrowing in the ooze, and we can well frame in our
+minds a picture of the little Fishes and other creatures attracted
+by the “will-o’-the-wisp” light, meeting with a sudden death in the
+cavernous jaws of this voracious deep-sea Fish.
+
+It is possible that in addition to the light given off by definite
+organs, the slime secreted by the skin either over the whole surface
+or certain circumscribed regions, may be phosphorescent, but how
+far this may serve as a means of illumination must remain a matter
+of conjecture. The Crustaceans are in some cases known to emit a
+phosphorescent fluid. The naturalists of H.M.S. _Investigator_
+found a brilliantly phosphorescent liquid in the glands at the base of
+the antennæ and elsewhere in certain deep-sea Shrimps, and one of the
+Cray-fish from great depths is said to have two definite spots on the
+body that emit a phosphorescent light.
+
+Several of the Star-fish and Brittle-stars from the abyss are known to
+be brilliantly phosphorescent, and there are some vivid accounts of the
+light given off by Worms and various kinds of deep-sea Polyps found in
+the dredge.
+
+It is possible that some of the more minute forms of life that occur on
+the mud at the bottom may also be phosphorescent. The _Phæodaria_,
+a family of Radiolarians peculiar to deep water, provided with thick
+heavy shells, have a curious organ in their bodies which may be capable
+of emitting light. If this is the case, it is not unreasonable to
+suppose that the vast tracts on the bed of the ocean may be faintly
+luminous like the surface of the sea on a calm night.
+
+Among the other characters must be mentioned a very prevalent
+deficiency in the salts contained in the skeletons of these animals.
+The skin of the Fish is usually soft and velvety to the touch, the
+scales being either very thin and few in number or altogether missing;
+the bones are described as being so soft that it is easy to pass a
+needle through them. The shells of the Crustaceans, although frequently
+drawn out into numerous long and pointed spines, are usually deficient
+in carbonate of lime. The shells of the Molluscs are, when compared
+with those that live in shallower water, thin and brittle. The Corals
+do not seem in this respect to show much variation from their shallow
+water relations. Some of the solitary forms seem to have rather thinner
+shells, but the colonial genera have, as a rule, as good a support of
+carbonate of lime in the abyss as elsewhere.
+
+Before proceeding to the next character, it is necessary to digress a
+little to consider the food of the animals in the abyss. In the absence
+of any direct sunlight there can be no vegetable growth, all of the
+animals must therefore be carnivorous. The food must be either the
+living bodies of the truly abysmal animals, or the dead bodies of those
+that fall from the surface waters.
+
+It is probable that the bodies of Fish and the larger Invertebrates
+only rarely reach the bottom, as they have to run the gauntlet of many
+different forms of life living within 100 fathoms of the surface. When,
+therefore, such a prize does fall to the luck of a deep-sea Fish,
+it is important that it should have accommodation for it before the
+neighbours come to share the meal. This may be the cause of the fact
+that deep-sea Fish have, as a general rule, jaws and stomach that are
+extravagantly large, even for a carnivorous creature. The width of the
+gape and the extensibility of the stomach reach their highest grade
+in some of the deep-sea Eels, which have been found containing Fish
+actually larger than themselves. In these cases the stomach and the
+body wall hang down from the under side of the Eel’s body in the form
+of an enormous membranous sac containing the prey.
+
+We have now considered very briefly some of the principal modifications
+of structure exhibited by the animals of the deep-sea, but before
+leaving the subject altogether it is necessary to refer to a few of
+the more characteristic and remarkable forms.
+
+Although it may be considered to be one of the greatest scientific
+triumphs of the century to have discovered the existence of animal life
+in a region, which nearly all the distinguished men of science of the
+last generation believed to be as lifeless as the moon, the revelations
+of the dredge brought with them a certain amount of disappointment.
+
+The study of the crust of the earth has revealed to us the fact that in
+times long since gone by, there existed not only the hairy Mammoths,
+the Iguanodons, and many other terrestrial monsters; but that the sea
+was peopled with certain Reptiles, Fish, Molluscs, Echinoderms and
+Crustaceans, which are now believed to be extinct.
+
+When it was first discovered that some forms of animal life had
+attached themselves to a telegraph cable lying in 1200 fathoms, and
+that it was therefore a fact that life existed in very deep water,
+a successful application was made by scientific men to the British
+Government to assist them in a thorough survey of this hitherto unknown
+field of investigation.
+
+The result of the voyages of H.M.S. _Lightning_ and H.M.S.
+_Porcupine_ was to prove the existence in water of 1000 fathoms in
+depth of a rich Fauna of rare and very remarkable animals. Among them
+were several new genera of Sea-lilies and a very curious Heart-urchin.
+The Sea-lilies that were then known to live in shallow water were very
+few in number, and nearly all of them were free and unattached. Now,
+in past times in the history of the earth different genera and species
+of stalked Crinoids or Sea-lilies were very plentiful, and from their
+abundance in certain geological deposits, it is believed that they
+lived in enormous numbers. The discovery of the new genera of stalked
+Crinoids in the abyss suggested that possibly there might be found
+several other families of extinct animals still surviving in the deep
+sea. This view was supported by the Heart-urchin, whose shell showed
+some striking peculiarities that were only known in fossil genera.
+
+But the hopes that were felt, even if they were not always expressed,
+were doomed to disappointment. No living Ichthyosauruses or
+Plesiosauruses, none of the remarkable Ganoid fish of Devonian times,
+no Trilobites, no Cystoids nor Blastoids,--in fact none of the most
+interesting of the fossil types rewarded the investigators of the
+_Challenger_ and subsequent expeditions.
+
+It is perfectly clear to us now that, taken as a whole, the deep-sea
+Fauna is not more ancient in character than any other Fauna. It is
+true that a few genera, such as those just referred to, have survived,
+probably from very ancient times, without much modification; but the
+vast majority of forms are simply shallow water animals, which have
+been profoundly modified in structure, and adapted to the peculiar
+conditions of existence in the great depths of the ocean.
+
+
+
+
+                             CHAPTER VII.
+
+                     COMMENSALISM AND PARASITISM.
+
+
+The term Symbiosis has been applied by naturalists to the phenomenon of
+the living together for mutual help or protection of different species
+of animals or plants. It is a well-known fact, to all those who have
+taken an interest in any large group of animals, that some species are
+nearly always associated with other species, belonging perhaps to a
+different class altogether, and very frequently mimicking them in form
+or colour. At first it might be thought that most of these cases could
+be dismissed as cases of parasitism; but when the careful observer
+notices that neither of the species is injured by the association, the
+conditions of the partnership are evidently very different to those of
+a blood-sucking parasite and its ungracious host.
+
+Besides the words Symbiosis and Parasitism, the terms Commensalism
+and Mutualism have been applied to various cases of association of
+different species of animals; but with the increase of our knowledge
+of the habits of animals, it is becoming more and more difficult to
+classify all known cases under these four heads, and the words are
+consequently often used with widely different meanings.
+
+It will be perhaps the best plan to adopt in this book, to avoid
+any attempt to give definitions of these terms until a few cases
+illustrative of each have been described.
+
+One of the commonest objects of the sea-shore is the Hermit-crab.
+From the open mouth of what is apparently an empty shell a bundle of
+claws and legs may be seen to protrude; turn the shell over and it
+will scamper away into the deeper parts of a rock pool. This is an
+association of a living Crab with the shell of an animal that is dead;
+but if the Hermit-crab be extracted it will be seen that it has a soft
+and twisted tail, quite unlike that of the shore Crabs, and that it
+could not possibly live for any length of time without the shelter and
+protection afforded by the shell that it has appropriated to itself.
+The Hermit-crab in the course of its life increases in size, and when
+it gets too big for the shell it is living in, it goes in search of
+another a little bit larger and changes, until at last it attains to
+the size and dignity that requires a full-grown Whelk shell.
+
+In the waters of our coast just beyond the low tide mark we often find
+that the shell containing a Hermit-crab bears a Sea-anemone which
+belongs to a species rarely found anywhere excepting in association
+with a Hermit-crab. Moreover, the Anemone is always seated in a
+definite position on the shell, so that its mouth is turned towards
+the jaws of the Hermit-crab when it is extended, enabling it to catch
+any morsels of food that escape the mouth of its comrade. When the
+Hermit-crab has grown too large for its shell, and moves into a new
+one, the Anemone moves too, and takes up the same position on the
+new shell that it occupied on the old one, and the companionship is
+continued in this manner throughout life.
+
+The advantage of this arrangement to the Anemone is obvious, for it can
+not only obtain its food after the manner of the other Anemones, but
+it also gains a share of the food of the Hermit-crab. The advantage to
+the Crab is not so apparent, but it is probable that the Anemone, being
+very distasteful to many Fish and other animals, acts as a protector to
+it. The facts that Hermit-crabs are extremely shy, darting back into
+their shells when there is the slightest sign of danger, and that they
+are extremely good bait for many kinds of Fish, suggest very forcibly
+that they have many enemies among the inhabitants of the deep. Any
+such covering as that afforded by the Anemone, which hides to a great
+extent the character of the shell, would be of protective value, but
+when to that is added the fact that the Anemone, which affords this
+covering, is avoided as uneatable and distasteful by carnivorous Fish,
+there can be no doubt whatever of the assistance that it renders to the
+Crab in return for its board. If any of my readers are sceptical about
+the distastefulness of Sea-anemones I would ask them to think of any
+instance in which Sea-anemones are used for bait, and then to try the
+experiment of offering pieces of them to the Fish in an aquarium.
+
+An observation by Prof. Möbius in the Indian Ocean affords another
+example of the use of Sea-anemones in this respect. He discovered a
+little Crab called _Melia tesselata_ which carried about in each
+of its claws a Sea-anemone. When the Crab was alarmed it held them up
+in much the same way that a man holds a torch, as if it would call
+attention to the fact that it had these terrible weapons at hand. When
+the Anemones were removed it carefully searched for them, and held them
+up again when found, and even when the Anemone was cut into pieces the
+Crab diligently collected them, arranged them as far as possible in
+their proper places, and held them up together.
+
+                      [Illustration: +Fig. 37.+
+         Hermit-crab protruding from its hole in the sponge.]
+
+But Sea-anemones are not the only animals that seem to be generally
+distasteful to Fish. Many of the Sponges are free from attack, and
+could serve as a protection to the Hermit-crabs. On our own coast
+a small brown Sponge is not infrequently brought up in the dredge
+surrounding and protecting a Hermit-crab; and hidden somewhere in the
+substance of the sponge, there may always be found a small shell which
+lies at the end of the hole in which the Crab lives.
+
+This association is, from the Crab’s point of view, a more advantageous
+one than that with the Sea-anemone, for it does away with the
+necessity of any changes of shell, the Crab and the Sponge growing up
+together. The history of the companionship is probably as follows:--A
+small Hermit-crab takes for its shelter a small Gastropod shell, and
+upon this shell a Sponge larva settles, grows and spreads, until it
+surrounds the whole of it except the hole from which the Crab emerges.
+As the Sponge grows still further in thickness the margin over-lapping
+the aperture of the shell expands, leaving a conical cavity leading
+from the exterior to the shell, surrounded, of course, by Sponge
+structure, in which the Crab lives. Thus as the Hermit-crab increases
+in size it is ever provided with a wider hole to accommodate its body
+by the growth of the Sponge, and the little shell wholly deserted
+remains as a token of the past history of the pair. But in the later
+stages of growth a third creature is taken into the partnership, in
+the person of a small segmented Worm which lives in the hole with
+the Hermit-Crab. The need for this third person seems to be one of a
+sanitary character. The cleanliness of the Hermit-crab, which has
+no sponge to protect it, is provided for by the simple expedient of
+frequent changes into a new home. In this case it is arranged for by
+taking into the home, on what we may call board wages, an efficient
+scavenger.
+
+                      [Illustration: +Fig. 38.+
+  Section through a sponge (_D_) showing _A_, the little shell; _B_,
+     the worm; _C_, the Hermit-crabs in their natural positions.]
+
+In this remarkable association, then, no less than four species
+belonging to four different groups of animals are concerned. First of
+all there is the _Gastropod_ Mollusc, which forms a shell for the
+_Crustacean_ Hermit-crab to commence life in, then there is the
+_Sponge_ which protects, and afterwards forms a shelter and home
+for the Hermit-crab, and lastly, there is the _Annelid_ worm,
+which helps in its way to keep the house clean in return for the scraps
+of food that fall from the head partner’s table.
+
+A very similar association has recently been described by Bouvier from
+the Gulf of Aden and Red Sea waters. A number of simple solitary Corals
+were thrown into an aquarium by a French naturalist, some falling on
+their sides and some on their crowns, but he noticed that, after the
+lapse of some time, they were all in the erect position again with
+their crowns of tentacles expanded in the water. On carefully watching
+them he observed that at the base of each Coral there was a little hole
+from which emerged a small unsegmented Worm, belonging to a family that
+usually exhibits sand-burrowing propensities. These Worms were found to
+be the agents which restored the Corals to their erect positions. The
+advantage of this arrangement to the Worm was two-fold: it brought it
+into direct contact with the sand in which it searches for its food,
+and, at the same time, it brought the Coral into such a position as
+to hide and protect it from its enemies above in a most effectual
+manner. To the Coral it was obviously an advantage, in that it placed
+it in a position to expand its tentacles in search of the food it seeks
+in the water and prevented a death from suffocation. A more minute
+investigation of the Coral, however, revealed the facts that hidden
+in its substance there was a small Gastropod shell on which we may
+suppose both the Coral larva and the Worm settled when the partnership
+began, and that in association with the Worm there was a small bivalve
+Mollusc which probably acts as a scavenger in the manner of the Worm in
+the last mentioned case. Here again, then, there are three different
+species living together to their mutual advantage and commencing their
+association on the shell of a fourth species belonging to a different
+class of animals. What words can we apply to these associations? The
+Hermit-crab and the Anemone feed at “the same table” and therefore
+they afford a case of “Commensalism”; the Coral and the Worm are of
+advantage to one another, the former in shielding and protecting the
+latter and the latter in keeping the former in an upright position,
+but as they do not feed “at the same table” it is not a case of
+“Commensalism” but rather one of “Mutualism.”
+
+There are many cases, however, of the association of animals in which,
+although the advantage to one of the partners is clear, it is extremely
+difficult to say what benefit is derived by the other.
+
+Living in a tube on our coasts is a very common Worm called Sabella,
+and at the mouth of the tube a little Polyp may frequently be found
+which has received the fanciful name of the “Household god of the
+Sabellids” (_Lar Sabellarum_). The Polyp undoubtedly benefits
+by the currents of water which the Worm sets up when feeding, but it
+is difficult to see what advantage, if any, the worm gains from the
+presence of the Polyp.
+
+Again, some of the Trepangs are frequently inhabited by a little Fish
+called _Fierasfer_, which comes out from time to time to feed and
+“take the air,” but rapidly retreats into the body of the Trepang on
+the slightest alarm.
+
+                      [Illustration: +Fig. 39.+
+                     A Trepang, or sea-cucumber.]
+
+The large stinging Sea-anemones of the Coral often afford protection
+of a similar kind to a little Fish. Saville Kent gives a beautiful
+picture of a little bright red Fish swimming about on the disc of a
+large purple Sea-anemone, and he says that it darts into the mouth when
+alarmed. On our own coasts we may often observe a number of little
+Fish generally belonging to the Cod-family swimming round the disc and
+tentacles of the large Jelly-fishes, and these, when frightened, swim
+vigorously toward the under surface of the umbrella and seek security
+there. Sometimes as many as a hundred or more of them may be seen
+hovering round one large Jelly-fish, and we can hardly estimate how
+valuable to our sea fisheries is the protection afforded by these great
+Medusæ to the young Fish-fry. (_See Frontispiece._)
+
+It was not my purpose in writing this book to point out the practical
+value of scientific investigation, but this history of the Jelly-fish
+and Codling cannot be passed without comment. The Jelly-fish might
+readily be regarded by the ignorant not only as useless to man, but,
+in so far as they sometimes choke his fishing nets and sting his hands
+and arms, a positive nuisance to him. Scientific investigation when
+pursued by properly qualified persons for its own sake, and not for
+any definite commercial results that may possibly come out of it,
+frequently reveals facts of the utmost importance, such as the one that
+has just been mentioned.
+
+There are some other cases of association which would on first
+consideration be called undoubtedly cases of parasitism, but as this
+term has been used somewhat vaguely in popular English, it would be
+well, before proceeding further, to place before the reader a definite
+statement of the sense in which the word is used in this book.
+
+In many of the cases that we have mentioned hitherto of animals
+living together, no apparent injury is inflicted upon either of the
+associates, but a very definite and decided advantage accrues to each
+of them, by the association.
+
+In other cases, however, whilst no apparent injury is inflicted on
+either, the advantage of the partnership falls entirely to one of them.
+
+In a third set of cases one of the associates feeds upon the blood or
+tissues of the other without rendering it any service in return, and
+consequently inflicts either temporary or permanent injury. These are
+cases of parasitism. In such an association the animal that inflicts
+the injury is called the “parasite,” and the one that receives it, the
+“host.”
+
+One difficulty the naturalist has to contend with in trying to use
+these terms correctly is that of finding out whether in any particular
+case an injury is inflicted or not; another is that of determining
+whether those animals should be called parasites which injure, alter,
+or destroy the tissues of their hosts without feeding upon them.
+
+A few cases will throw more light upon the subject than any further
+discussion of the difficulties surrounding the application of these
+terms.
+
+One of the commonest Corals to be found upon the coral-reefs of both
+the Old and New world is one called _Millepora_. In the Millepores
+of the Pacific region we very frequently find a number of Barnacles
+(called _Pyrgoma milleporæ_) so deeply buried in the substance of
+the Coral that their presence is indicated only by a small oval hole on
+the surface. There can be little doubt that in the course of the growth
+of these Barnacles they distort, if they do not actually destroy, some
+of the connecting canals of the Coral in their immediate neighbourhood,
+but their food is derived entirely from the water that surrounds
+the Coral and not any portion of it from the cells or tissues of the
+Coral-polyps themselves.
+
+There is a great deal of difference in the Millepores from one and the
+same coral-reef, in the extent to which the Barnacles have attacked
+them. In some specimens large areas of the Coral are beset with the
+little holes, in others only one or two may be found on the whole
+colony, whilst others again are quite free from them. Now when we
+compare carefully the anatomy of those Millepores with the Barnacles
+and those without them, no single sign or symptom can be found that the
+vigour or strength of the former is in any way impaired. If then there
+is no evidence that the Barnacles are parasitic, in the sense that they
+are injurious to the Millepores, we must next inquire whether they
+could possibly be of any service to them.
+
+The polyps of the Millepores feed after the manner of the polyps of
+other Corals, upon minute organisms floating in the sea; these they
+paralyse and capture by means of tentacles bearing stinging cells. The
+food is in the ordinary course brought within reach of the tentacles
+by the tides that sweep over the reefs. The Barnacles also feed upon
+minute organisms of the same kind, but they are provided with six pairs
+of long feathery legs which by a curious vibratory movement create
+currents in the water. When there are many Barnacles in close proximity
+to one another it is quite probable that the water is considerably
+disturbed by these currents, and the constant and rapid flow of fresh
+water bearing food-organisms benefits, not only the Barnacles, but also
+the Millepore polyps in their neighbourhood.
+
+Thus the Barnacles _may_ be a benefit to the Millepores in which
+they live. It cannot be asserted, however, that this probability is
+a proved fact. A great deal more knowledge about the rate of growth
+of the Corals which are and are not affected, must be acquired before
+such an assertion could be made: but the _probability_ that the
+Barnacles may be of service is sufficient to cause us to hesitate
+before branding them with the epithet of “parasites.”
+
+This particular case, which has been given above in some detail, may
+be regarded, in a sense, as a test case, because other animals besides
+the Barnacles, which gain their food by producing currents, are found
+in Corals. Such are the tubicolous Worms, bivalve Molluscs, and certain
+Sponges. So plentiful are these on the older branches of some Corals,
+that quite a rich Fauna belonging to several groups of animals may
+be found by carefully studying them. These might all be dismissed as
+parasites by the non-inquisitive mind, but many of them, at any rate,
+may be regarded by the more cautious naturalist as not injurious, and
+others perhaps as positively beneficial to the Coral on which they
+live. There is a very curious case of symbiosis mentioned by Semper,
+which may be related here as similar in some respects to those above
+quoted.
+
+                      [Illustration: +Fig. 40.+
+              A Crab-gall on a branch of a Seriatopora.]
+
+On the shores of the Philippine Islands and in other parts of the
+Pacific Ocean there is a very common coral named _Seriatopora_.
+It is composed of numerous delicate branches, terminating in fine
+pointed extremities, forming hemispherical shrub-like masses, six or
+eight inches in diameter. Semper noticed that on some of the branches
+of these Corals there were little heart-shaped swellings, which had the
+appearance of malformations or structures corresponding to the galls on
+the leaves and branches of trees. Each of these swellings contained a
+cavity, communicating with the exterior by two minute holes, in which
+there was imprisoned a small Crab.
+
+By the examination of a large number of specimens, Semper came to
+the conclusion that the history of these structures was somewhat as
+follows. The young Crab, when it settled down on the branch, produced
+an irritation which in some way caused a gall-like growth of the
+tissues of the Coral. This growth continued until it formed at first a
+case or sheath for the protection of the Crab, and eventually, as the
+Crab increased in size, a cage from which it could not do more than
+protrude its tentacles and claws when feeding.
+
+It seems very improbable that these cage-like swellings upon the branch
+can be of any great disadvantage to the Coral. It is true that they
+destroy the beautiful symmetry of the branch, and give it a distorted
+and diseased appearance; but this is only an æsthetic disadvantage,
+which does not probably count for much in the struggle for existence
+on the Coral-reef. To the Crab the arrangement is undoubtedly an
+advantage, as it gives it a secure position, free from the attack of
+its ordinary foes, where food is probably abundant and easily obtained.
+
+The skin of Whales is often beset with Barnacles; in fact some species
+of them are found nowhere else but on these Mammals. They are usually
+deeply embedded in the skin, only a small round hole through which the
+legs can be protruded, communicating with the exterior. These Barnacles
+do not feed upon the tissues and juices of the Whale, but, in the
+usual manner of the non-parasitic Barnacles, upon organisms that swim
+freely in the water. The advantage to the Barnacles is obvious, as the
+movements of the Whale through the water must bring them in reach of
+constant fresh supplies of food, but the benefit to the Whale is not
+so clear. It cannot be supposed for a moment that the Barnacles assist
+the Whales in their search for food, nor can they be regarded, when
+present in great numbers, as a protection to the skin by the strength
+afforded by their thick calcareous shells; at the same time there is no
+reason to suppose that their presence is an inconvenience or in any way
+harmful to the Whales.
+
+These cases of animals bearing on their bodies other creatures which
+are not in the strictest sense of the word parasites, are but instances
+of a phenomenon that is very widely spread among marine organisms.
+There are many cases, however, in which plants and inorganic foreign
+bodies play a very important part in the economy of animals.
+
+In our chapter on the free-swimming organisms of the ocean, mention has
+been made of the delicate and beautiful creatures called Radiolarians.
+Many years ago it was discovered that each of these animals bears
+in its protoplasm a number of little cells, which from their colour
+received the name of “the yellow cells.” It was clear from observation
+and experiment that they were neither organs nor products of the
+Radiolarian, but independent organisms belonging to the Vegetable
+Kingdom.
+
+More recently cells similar to these have been found in many of the
+Corals, in Worms, and other animals, and there can be no doubt now that
+when present they perform very important physiological functions which
+materially assist their host in its growth and development.
+
+So numerous are these “yellow cells” in some Polyps and so important
+must be their influence on their vital processes, that it may be
+confidently asserted that the Polyps could not continue to exist
+for long without them. In the genus _Millepora_, for example,
+no single specimen and no single fragment of a specimen that I have
+examined was devoid of them; and although the numbers vary considerably
+the most superficial canals of this Coral may in all cases be
+described as crowded with “yellow cells.” But as the “yellow cells” are
+certainly of great physiological importance to the Millepore, it is
+equally certain that the secretions and the protection afforded by the
+Millepore are of extreme importance to the “yellow cells.” In fact it
+is not going too far to say that the Millepore and its “yellow cells”
+are dependent upon one another for their existence, and the naturalist
+might say with a great deal of truth that this particular Coral is not,
+strictly speaking, animal in nature, but rather an animal and vegetable
+combination.
+
+Many years ago there was a bitter controversy among learned men on
+the question of the animal or vegetable nature of Corals. The great
+naturalist Linnæus, who was appealed to for his support by both parties
+to the controversy, took up a middle position, asserting that they were
+partly of the nature of animals and partly of the nature of plants,
+and hence the term “zoophytes,” _i.e._ animal-plants, came to be
+applied to them. There can be no doubt that in the end the position
+in the controversy, assumed by Linnæus, became untenable, and the
+supporters of the animal view of zoophytes won all along the line. It
+is curious, therefore, that we are now in a position, not to support
+the view of Linnæus, but to assert that some Corals are essentially a
+combination of animals and plants.
+
+Plants are of use to marine animals, however, in another manner.
+Mention has already been made of the way in which many animals
+resembling in colour, and even in form, certain kinds of sea-weeds,
+escape the attention of their enemies and hide for safety among the
+plants they simulate. Sometimes, however, the weeds will grow upon
+the shells of the animals, and thus hide them even more effectually.
+One of the most remarkable instances occurs in a Spider-crab that is
+common upon our own coasts. The _Inachus_, as it is called, is
+usually covered with a little forest of algæ, which do not grow there
+naturally, but are actually placed on the carapace by the Crab itself.
+If the plants be scraped off artificially the Crab will go in search
+of fresh ones, carefully chew the bases until they are soft, and then
+deliberately decorate the carapace with them as before.
+
+There are some Molluscs that artificially decorate themselves with
+little shells and other objects in such a manner as to completely
+hide their general form. One of the most remarkable instances of this
+occurs in the Gastropod _Xenophora_, which covers its own shell
+with numbers of others belonging to a smaller species, so that in
+the natural state it has the appearance of a conglomerate of shells.
+The manner in which the smaller shells are fixed has not yet been
+described, but from the orderly arrangement which they exhibit in some
+cases there can be little doubt that they are deliberately placed in
+position by the Gastropod itself and not attached by accidental contact.
+
+In both these cases it is clear that the reason for the phenomena
+described is that of affording a covering or mantle, which hides or
+obscures the real form and character of the living animals.
+
+Many of the Worms use little bits of shell and grains of sand to
+build up a tube for the protection of their bodies. One of these--the
+_Terebella_--is very common on our shores, the sandy tubes ending
+in a tuft of fine filaments, and decorated all over with tiny little
+stones or shells, projecting an inch or two from the surface of the
+sand. In some localities these tubes may be found in thousands when the
+tide is low.
+
+Another form--_Pectinaria_--constructs much firmer tubes, which
+retain their cylindrical shape after the death of the animal. In the
+process of construction this Worm must carefully select the grains
+of sand, for when the tube is examined with a magnifying glass the
+particles will be seen to be of almost exactly the same size, and
+arranged in their places with a mathematical precision.
+
+But Worms are not by any means the only animals that use the sand in
+this manner for the protection of their bodies. There are some kinds
+of Polyps, belonging to the family _Zonathidæ_, a peculiar group
+of Sea-anemones, in which the body-wall is considerably strengthened
+by foreign bodies of various kinds. The _Zoanthus_ does not, like
+the Terebella-worm, form a tube or case in which the body can freely
+move up or down, but sticks the grains of sand into its skin, so that
+they become in the older forms deeply buried in the tissues and give a
+considerable support to the body-wall.
+
+The _Cerianthus_--another Sea-anemone--forms a tube which is
+partly composed of a matted network of stinging threads, and partly of
+the mud in which the animal lives.
+
+The use of foreign inorganic substances for the protection or
+concealment of animals is not, strictly speaking, however, a part
+of the subject-matter of this chapter, which was intended for the
+consideration of the associations of two different kinds of living
+organisms.
+
+The subject of Parasitism must now be considered, a subject which
+presents so many features of interest that it is possible here only
+to touch on a few points of general importance. It is a well-known
+truism to say that Parasitism, whether in human society or in animal
+life, leads to degeneration; but there are degrees of parasitism among
+animals, and consequently degrees of degeneration exhibited by animal
+parasites. We may roughly divide them into two classes, the outside or
+skin parasites and the internal parasites, the latter being invariably
+far more modified in structure and in development than the former.
+
+Among the terrestrial animals we find a great number of external
+parasites, such as the Fleas and the Bugs, which are only slightly
+modified, as in the loss of their wings, owing to their habits, and can
+live an active, if not a very prosperous, life for some length of time
+apart from the society of their hosts. There are others, such as the
+Mosquitoes, Ticks, and Leeches, which are only occasional parasites;
+that is to say, they will suck the blood of another animal when the
+opportunity is presented, but failing that, are able to continue their
+life and their race independently. It is not surprising, however, that
+the terrestrial Vertebrates should be thus subjected to the attacks of
+these parasites, as their feathery or hairy skin affords a shelter and
+a foothold, from which the efforts of their hosts to dislodge them are
+exercised in vain.
+
+The skin of Fish, although covered with over-lapping scales, is smooth
+and slippery, and with the rapid movement through the water many of the
+forms of parasites of the types we meet on land would, if they existed
+in the sea at all, find a difficulty in securing an attachment. It is,
+however, provided with another means of defence against skin parasites,
+in the possession of numerous mucous glands which keep the body bathed
+with a slimy fluid.
+
+Everyone must have noticed the slime that exudes from freshly killed
+Fish, and if the finger be pressed along the skin it is possible to
+see the openings of the glands as the slime is squeezed out. In the
+majority of Fish the openings of the glands are most easily seen on the
+jaws and the flap of the gill cover.
+
+We must remember that the sea is in most places teeming with the larvæ
+of Worms, Barnacles and Zoophytes, and the spores of Algæ and Fungi
+of various kinds. Logs of wood, the iron supports of piers, and the
+bottoms of ships become covered with various fixed forms of animal and
+vegetable life when submerged in the sea-water for even a few weeks.
+How is it, then, that the bodies of the Fish are usually so clean and
+wholesome? The answer to this question is probably to be found in the
+slime which, passing continuously over the skin, removes the larvæ and
+the spores before they can secure a firm attachment.
+
+The Crabs, Lobsters and other Crustaceans free themselves from their
+skin parasites at every moult, but in some of the large, old Lobsters
+and Crabs that are caught a considerable number of Worms, Barnacles and
+weeds are frequently found firmly-fixed to the carapace and claws. The
+Limpets and Winkles of our rock pools are often covered with a little
+forest of Algæ.
+
+The shells of other Molluscs are, however, kept remarkably clean, and
+the method by which they destroy the spores, etc. that settle upon them
+is not yet fully understood.
+
+One of the most serious of the external parasites is the Hag-fish. This
+remarkable animal is eel-like in shape, although very different indeed,
+anatomically, from all the true Fishes, and buries its head in the skin
+of the Cod and other Fishes as it feeds upon their flesh. In some cases
+the whole body of the Hag gets inside the host, and it thus becomes an
+internal parasite. It causes an immense destruction of valuable food
+fish in some districts.
+
+Closely related to the Hag is the marine Lamprey, which fastens itself
+to Salmon by its suctorial mouth, causing considerable wounds. This
+parasite sometimes reaches to a length of two feet, and is often
+carried many miles up the river by the host to which it is attached.
+
+Most of the Leeches occur either in fresh water or in damp forests and
+marshy places. There is one, however, named _Pontobdella_, which
+is found only in sea-water. It is difficult to give an exact statement
+as to its size, because, like all its relations, it is capable of
+very extensive movements of expansion and contraction, but the
+_Pontobdella_ is large for a Leech, and when moderately contracted
+it may be two or three inches in length. The body of this Leech is
+covered with small tubercles, and it has a large round sucker at each
+end. Its favourite hosts are the Sharks and Rays, but as it usually
+drops back into the water when these Fish are hoisted on to the deck it
+is not very commonly seen in the fishermen’s boats.
+
+The most common external parasites of Fish are the Fish-lice. Most of
+these are little Crustaceans, belonging to a group which includes the
+Wood-louse. They have curiously flattened bodies, provided with short,
+bent legs, terminating in sharp hooks, by which they adhere to the body
+of the Fish and crawl about over the skin. Some of these parasites seem
+to prefer the tongue as a resting-place, the genus _Glossobius_,
+for example, being found in this position on the Flying-fish of both
+the Pacific and Atlantic Oceans. In _Glossobius_ we find a very
+remarkable difference in size and form between the males and females,
+a condition of affairs which is of very common occurrence among the
+parasitic Crustaceans. The male in this particular case is so small
+that it is entirely concealed beneath the tail of the female. In
+another genus a still more interesting condition has been observed, the
+small young forms which are males growing up, and changing in later
+life into females.
+
+There is a remarkable parasite called _Sacculina_ which may
+sometimes be found on the under side of the tail in Crabs. In shape it
+is like a small pea or bean, and is attached to its host by a number
+of root-like processes, which penetrate through the skin and burrow
+deeply into the subjacent tissues. It would be quite impossible to tell
+to what group of animals this parasite belongs by the study of the
+adult form alone. It is, in fact, little more than a skin full of eggs.
+When the development of the eggs is watched, however, it is observed
+that the young _Sacculina_ as it is hatched is very much like
+the Nauplius larva of a Barnacle. The later stages of the development
+prove that whatever may happen to the adult the _Sacculina_ must
+be related to the group of the Cirripedia. Later on it is found that
+the females settle down on a Crab, lose all their limbs and other
+Cirripedian characters, and finally degenerate into a mere palpitating
+sac of eggs.
+
+The males never pass beyond the second stage of development known as
+the Cypris stage. Several of them may usually be found attached to the
+female, and although they always remain extremely minute they do not
+lose entirely their Crustacean features.
+
+For those who are in search of parasites, however, there is no more
+fruitful ground than the gills. That these organs should be a good
+place for attack is not surprising, when we consider that to maintain
+the respiration of the animal a constant flow of sea-water over them
+must be kept up, and this must bring with it many larval forms which
+may take the opportunity to attach themselves as they pass through the
+meshes of the gill filaments. Moreover, it is in the gills particularly
+that the blood current comes into closest contact with the water, and
+it requires but a little puncture on the part of the young parasite to
+reach a constant supply of this nourishing fluid.
+
+It is in the gill-chambers that we find most frequently representatives
+of that interesting group of animals, the parasitic Copepods.
+
+                      [Illustration: +Fig. 41.+
+                         A parasitic Copepod.]
+
+It would be difficult to recognise them as Copepods if we were to judge
+by their adult characters alone. Unlike the brisk, brightly-coloured
+creatures with long rowing antennæ that we have described above as
+living a free life in the surface waters of the ocean, these parasites
+have a white sac-like body, with short blunt processes representing the
+legs, no eye, and generally two long thread-like bags of eggs attached
+to the sides of the rudimentary tail. As we found in the case of the
+_Sacculina_, the true zoological position of these parasites can
+only be determined by reference to their developmental history.
+
+In the gill-chamber of the Prawns we find a very much modified
+parasite, which is closely allied to those skin parasites of Fishes
+mentioned above. Many of my readers may have noticed that in some
+Prawns there is a wart-like swelling on one side of the neck. If
+the skin be removed it will be observed that this is in reality a
+cup-shaped protrusion on the wall of the gill-chamber covering a
+little, flat, soft animal. In past times it was thought that this
+was a young flat fish, and a wonderful story of its development was
+fabricated on the strength of this error. It is now known to be one of
+these extremely degenerate Isopod parasites called _Bopyrus_.
+
+It is a curious fact that there is very rarely indeed more than one
+of these parasites on a single Prawn. If there is one in the right
+gill-chamber there are none in the left, and _vice versâ_. It
+is difficult to find a satisfactory explanation for this, for it is
+not at all probable that, during the lives of the many hundreds of
+Prawns that have been examined, only one larva has passed through the
+gill-chamber of each individual. The explanation must be looked for
+in some hitherto unknown influence which the parasite has upon the
+constitution of the host, rendering it unsuitable for the attachment
+of another _Bopyrus_ of the same habits. The case is by no means
+unique. There are several instances of Fish and other animals that bear
+one, and never more than one, parasite of a particular species.
+
+A few words must now be added about the internal parasites of marine
+animals. The subject is really an immensely wide one; for the
+intestines, body cavities, and even blood-vessels of Fish are liable
+to the attacks of many different forms of Flukes, Tape-worms, and
+other kinds of parasites which are not even known by name, perhaps
+fortunately, to the general public.
+
+The life-history of some Flukes that occur in terrestrial animals
+has been satisfactorily worked out, and we know that, in most cases,
+they must infest two different hosts before they can reach maturity.
+The first of these hosts is usually an Invertebrate, and the second a
+Vertebrate animal. Moreover, it is known that the larvæ are extremely
+particular in their choice of the first host, attacking one species,
+and one species only, of Snail or Slug, or whatever Invertebrate
+its first host may be. If the first host dies a natural death or
+is swallowed by any other animal than the parasite’s proper second
+host, it--that is to say, the parasite--dies. It seems probable that
+the Flukes that infest the intestines of marine animals pass through
+some similar life-history, but owing to the great difficulties that
+confront the observer their development has not yet been thoroughly
+investigated. Similarly the life-histories of the Tape-worms, with
+which a very large number of marine animals are infested, are not
+yet known to us. It is comforting to know, after looking through the
+volumes of papers on these internal parasites of marine animals, that
+none of them have been shown to be, even occasionally, parasitic upon
+man, and we can continue our Fish diet without any misgivings on that
+score. An exception must, however, be made to this statement for the
+semi-marine Salmon and Sturgeon, which are suspected of being the
+first hosts of a human Tape-worm.
+
+It is perhaps unsatisfactory to dismiss the internal parasites of
+marine animals with so few words, but I feel compelled to do so, not
+only because I have nearly outrun the limits of space, but because
+we possess so little positive information on the subject, which is of
+greatest interest to us here, of their developmental history. Lists
+of species infesting different Fish and Whales could be published, a
+statement of the points of anatomical importance which distinguish
+the families could be written, but they would present few features of
+interest to the general reader.
+
+It may be well to point out before the chapter is closed, however, that
+there is probably no branch of our subject that is so little known and
+presents such a wide and important field for future investigation as
+the life-histories of these marine parasites.
+
+
+
+
+                             CHAPTER VIII.
+
+                    THE ORIGIN OF THE MARINE FAUNA.
+
+
+When we survey the distribution of living organisms over the surface
+of the globe, we cannot fail to be impressed with the enormous range
+in the characters of the physical conditions which are capable of
+supporting animal and vegetable life. Thus we find Birds flying in the
+sunlight of the cold and very light atmosphere of the mountain tops,
+and Fishes swimming in the chill darkness of the depths of the ocean,
+supporting a pressure of two tons to every square inch of their bodies.
+We find Algæ, which give the snow sometimes the name of “Red snow,”
+flourishing at temperatures below the freezing point of water, and we
+meet with Insect larvæ swimming freely in the water of the hot springs.
+Some sea-water animals can only be induced to live in the aquarium when
+the water is kept as pure as it is in the open sea, and languish and
+die as soon as any impurity occurs; on the other hand, several of the
+Crustaceans seem to flourish best in stinking and putrescent pools.
+The desert, the forest, the swamp, the lake, the river, as well as the
+surface and the bottom of the sea have each their characteristic set of
+animals and plants modified in structure and form to support life in
+their natural habitats.
+
+There can be no doubt that at the time when animals and plants first
+made their appearance upon the earth, their distribution was far more
+limited than it is now, and that all the adaptations to life in special
+and extraordinary conditions have been acquired in the course of
+evolution by organisms which originally existed in one particular zone
+of the earth.
+
+The reasons which have led scientific men to this opinion are manifold,
+but not the least important of them are those based upon the presence
+of organs or rudiments of organs of animals of the present time, which
+could only have been called into existence at a period when their
+ancestors had an altogether different habit of life.
+
+For example, in the Birds and Reptiles, as well as in the Mammals,
+the presence of openings in the throat during the early stages of
+development, similar in their position, in their blood-vessels and in
+other respects to the openings of the gills in Fishes, indicates that
+their ancestors in remote periods lived in water and not on dry land.
+
+Again the presence of rudimentary eyes in the Mole and other
+subterranean animals indicates that at one time its ancestors must have
+lived in the light of the day. The characters of the embryos of some
+of the land and fresh water Snails proves that they are derived from
+ancestors that lived in the sea.
+
+When we collect together all the evidence of this kind and place it
+side by side with the facts revealed to us by Geology, the irresistible
+conclusion is arrived at that all animals are originally derived from
+ancestors that lived in the sea. And when we consult the botanists and
+find that they are agreed that all plants must have had a marine origin
+also, the case for the sea being the original home of living organisms
+may be said to be completed.
+
+It is difficult to picture to ourselves the condition of the earth in
+those very distant times, when the dry land bore no forests nor grass,
+the air supported no Birds nor Butterflies, and in the rivers and lakes
+swam no Fish nor Frogs. It must have been “dry” land indeed, when
+there were no trees to attract the rain clouds and no herbs or mosses
+to retain the moisture on the ground. The rivers must have risen and
+fallen with great rapidity as they carried away the rain that fell in
+cloud-bursts on the mountain tops.
+
+But speculation on the character of the land in those times is not
+within the scope of this work, and we must turn again to the sea to
+inquire where the primordial animals and plants lived in the days of a
+lifeless land.
+
+We have seen that in the sea there are three possible habitats for
+animals and two for plants. The surface waters of the great oceans
+bear a characteristic population of animals and plants, the bottom of
+the sea supports a considerable number of animals but no plants, and
+lastly the shallow waters exhibit an immense variety of Sea-weeds,
+Fish, Worms, and other creatures. Which of these three was the original
+cradle of the great classes of animals and plants?
+
+The early discovery of certain animals in very deep water which are
+closely allied to, if not identical with, some fossils of early
+geological strata, suggested the idea that a very primordial set of
+creatures might be found at the bottom of the sea when it was more
+thoroughly investigated; but as I have pointed out in a previous
+chapter the hopes of those who anticipated the discovery of a rich
+Fauna of “living fossils” were doomed to disappointment.
+
+It is not probable, however, that the abyss of the oceans could have
+been the cradle of life, even if it had shown a more ancient Fauna than
+it actually does.
+
+We cannot tell in what form life first appeared upon the earth.
+Whether the unstable living substance called Protoplasm was in the
+earliest conditions of the globe formed spontaneously by the chance
+combination of its elements, or whether some germ or other made a
+hazardous journey through space from another planet enwrapped in the
+casing of a meteorite, are questions upon which no light has yet been
+thrown by scientific observation or speculation; but this can be said,
+that at a very early period in the history of life upon the earth the
+simple green plants must have played an important part. It is on the
+substances that are formed by the activity of this green coloured
+substance that all plants and animals are directly or indirectly
+dependent for their food in the present-day economy of Nature, and we
+are forced to believe that, whatever may have been the form of the
+earliest living things, Chlorophyll--the green coloured substance of
+plants--must have had an extremely ancient origin.
+
+Now, in the darkness of the ocean depths Chlorophyll does not and
+cannot exist; for it is one of its characteristic features that it
+is active only in the rays of direct sunlight; and, therefore, it is
+extremely improbable that the cradle of the marine Fauna could have
+been there. We are then left with two alternatives. It must have been
+either at the bottom of the shallow waters or on the surface of the
+seas.
+
+Both of these sites have had their advocates, but the balance of
+opinion has now turned decidedly in favour of the first of them--the
+shallow waters. It is not easy to explain the reasons for this view
+without assuming a fairly complete knowledge on the part of the reader
+of the various forms of life that are found in the sea, but still a
+few words of explanation may be written to indicate that the view is a
+reasonable one.
+
+In the first place we find, when we take a general survey of the
+animals that live in the surface water, that they are all specially
+modified in some way or another in structure or development in
+adaptation to the peculiar conditions of their life. The long spines
+of the Foraminifers and the Crustacean larvæ, the air-bladders of the
+Portuguese men-of-war, the oil drops of the Copepods, the raft of the
+Mollusc _Janthina_ are, as we have seen, among the characters
+which distinguish this peculiar Fauna. Now, when we compare these
+surface-dwelling forms with their nearest relations in the shallow
+waters, the conclusion we come to is that these features have been
+acquired by the ancestors of the former, which may have been similar in
+some respects to those now living in shallow water.
+
+Some of the Gastropods of the shore-waters have a simple cup-shaped
+shell like that of the common Limpet, but the great majority of them
+have a shell that is twisted up into a spiral form. This twisting of
+the shell is, of course, due to the twisting of the mantle or fold of
+skin which secretes the calcium carbonate of which the shell is mainly
+composed; and, when we study the internal anatomy of the animal we find
+that the shape of the mantle is associated with a loss of the organs
+of one side of the body. To put a long story into a few words, we may
+say that the Gastropods with twisted shells are lop-sided. Now when we
+examine the shells of the Gastropods that live in the surface waters
+of the ocean we notice that their shells are (with a few exceptions
+such as _Janthina_) perfectly symmetrical, and we might jump to
+the conclusion that this was due to a corresponding symmetry of the
+internal organs.
+
+Such a conclusion would, however, be an erroneous one, for the
+results of the careful anatomical study of these Molluscs proves most
+definitely, that although a false symmetry of the organs is often
+shown, there is a general suppression of the organs of one side of the
+body. A study of the development of these animals also shows, that
+in the early stages of their life, the shell is not symmetrical like
+that of the adult, but twisted into a spiral like that of a Whelk or
+a Periwinkle. These facts indicate that the surface-swimming Molluscs
+have passed through a stage in their evolution when their bodies
+were twisted up into a spiral shell, and that the false symmetry,
+which they exhibit in the adult condition, is an adaptation to
+their peculiar habits of life. The study of the group of Gastropods
+alone then does not give us any evidence in favour of the view that
+the surface-swimming Fauna is primitive; in fact, it proves almost
+conclusively that its share in the Fauna has been contributed from the
+shallow water districts.
+
+The group of the Tunicates affords similar evidence. There is no
+good reason for believing that the Salps and _Pyrosoma_ which
+drift about in the surface waters are more primitive than the fixed
+Sea-squirts of the rocks and Sea-weeds, in fact, the view is gaining
+ground, as our knowledge increases, that all the free Tunicates must
+have passed through a sessile ancestry. The evidence afforded by the
+Cœlenterates is not so potent. Several naturalists believe that some
+free-swimming form of Jelly-fish was the ancestor, and that the fixed
+Zoophyte was a stage introduced into the life-history at a later period
+in the evolution of the group. Others believe that the Zoophyte-stage
+came first and that the Jelly-fish was introduced, for the purpose
+of distributing, over a wide area, the eggs of the species. My own
+researches lead me to incline towards the latter view, but I feel that
+it is still far from being proved.
+
+A great deal more could be written upon this fascinating speculation
+about the origin of Life in the Sea. But it is still a speculation,
+and all that can be done at present is to weigh the evidence carefully
+and see in which way the scale seems to point. If I have succeeded in
+making clear to the general reader the nature of the evidence we can
+use in judging this question, and have indicated to him the direction
+in which it seems to _me_ to point, my task has been accomplished.
+
+
+
+
+                                INDEX.
+
+
+  A.
+
+  Air-bladders in Plankton, 90.
+
+  Alcyonarians of Coral-reef, 67.
+
+  Alcyonium, 42.
+
+  Alternation of Generations, 31, 93, 99.
+
+  Angler-fish, 39.
+
+  Azoic, without animal life, 9.
+
+
+  B.
+
+  Barbel, a tentacle on the lower jaw of Fish such as the Cod, 52, 139.
+
+  Barnacles, 40;
+    on Whale, 159.
+
+  Benthos, the animals living on the bottom of the sea, 110.
+
+  Blue-shark, 121.
+
+  Blue-whale, 126.
+
+  Bonito, 121.
+
+  Boring Mollusc, 43.
+
+  Bopyrus, 170.
+
+  Brachiolaria, 112.
+
+
+  C.
+
+  Caller-crab, 76.
+
+  Cetacea, 125.
+
+  Cilia, minute vibratile hair-like processes on the body of some small
+    animals, 111.
+
+  Cirripedia, a group of Crustacea to which the Barnacles belong, 168.
+
+  Cod-fish Family, 52.
+
+  Coffer-fish, 63.
+
+  Colour in shallow water animals, 31;
+    in deep-sea animals, 137.
+
+  Copepods, 86;
+    parasitic, 169.
+
+  Corals, 57.
+
+  Coral and Worm, 151.
+
+  Coral-reefs, 56;
+    shells of, 65;
+    Anemones of, 66;
+    alcyonarians of, 67;
+    different forms of, 68;
+    Fauna, of outer edge of, 78.
+
+  Crab-galls, 158.
+
+  Crab and Sea-weed, 162.
+
+  Crustaceans of the rocks, 48.
+
+  Ctenophores, a group of Cœlenterates, 85.
+
+  Currents, 16.
+
+  Cuttle-fish, 49.
+
+
+  D.
+
+  Density of Sea-water, 13.
+
+  Depths of the Sea, 10.
+
+  Diatoms, minute unicellular, plants, 23.
+
+
+  E.
+
+  Electric Organ, 37.
+
+  Eyes, 27;
+    of Scallops, 29;
+    of larval Tunicate, 30;
+    of Medusæ, 30;
+    of deep-sea animals, 138.
+
+
+  F.
+
+  Fauna, the animals living in a particular region considered as
+    a whole.
+
+  Filograna, 57.
+
+  Fish of the rocks, 51;
+    of the Coral-reefs, 63;
+    of the surface waters, 119;
+    of the deep-sea, 139.
+
+  Fish-lice, 167.
+
+  Flying-Fish, 120.
+
+  Fur-seal, 133.
+
+
+  G.
+
+  Gas reservoirs in Plankton, 90.
+
+  Gastropods of shallow water, 45;
+    of Plankton, 100.
+
+  Gelasimus, 76.
+
+  Globe-fish, 63.
+
+  Globigerina, 21, 104.
+
+
+  H.
+
+  Hag-fish, 166.
+
+  Halobates, 102.
+
+  Hermit-crab, 147.
+
+  Herrings, 123.
+
+  Hormiphora, 85.
+
+
+  I.
+
+  Inachus, 162.
+
+  Ipnops, 138.
+
+  Isopoda, a group of Crustaceans to which the Wood-louse belongs, 139.
+
+
+  J.
+
+  Janthina, 101.
+
+  Jelly-fish, 84, 92.
+
+  John Dory, 54.
+
+
+  L.
+
+  Lamprey, 166.
+
+  Larva, a young immature free individual differing in form from
+    the Parent.
+
+  Larvæ in surface waters, 109.
+
+  Leeches, 166.
+
+  Lithothamnion, 20, 57.
+
+  Lug-worm, 34.
+
+  Lump-sucker, 52.
+
+
+  M.
+
+  Mackerel, 124.
+
+  Madrepore, 57.
+
+  Mangrove-swamp, 73.
+
+  Medusæ, 31, 92.
+
+  Melia tesselata, 148.
+
+  Millepore and Barnacle, 155.
+
+  Mud-line, 19.
+
+
+  N.
+
+  Nauplius larva, 40, 115.
+
+  Nekton, 119.
+
+  Noctiluca, 109.
+
+
+  O.
+
+  Ooze, 21.
+
+
+  P.
+
+  Palolo Worm, 79.
+
+  Parasitism, 164.
+
+  Periophthalmus, 74.
+
+  Periwinkles, 45.
+
+  Pholas, 43.
+
+  Phosphorescence, 82, 107;
+    of deep-sea fauna, 140.
+
+  Phyllopteryx, 26.
+
+  Physalia, 97.
+
+  Pipe-fish, 25.
+
+  Plankton floating or drifting animals of a region considered as
+    a whole, 83.
+
+  Pluteus, 113.
+
+  Porpoise, 127.
+
+  Prawn, parasite of, 170.
+
+  Pteropod, 21, 102.
+
+  Pyrosoma, 108.
+
+
+  R.
+
+  Radiolarians, 22, 160.
+
+  Razor-shell, 35.
+
+  Red clay, 21.
+
+  Right-whale, 126.
+
+  Rocks, Fauna of, 39.
+
+
+  S.
+
+  Sabella, 153.
+
+  Sacculina, 168.
+
+  Salps, 98.
+
+  Sandy shores, Fauna of, 34.
+
+  Sargasso, 106.
+
+  Scallop, eyes of, 29.
+
+
+  Scopelus, 123.
+
+  Sea-anemones, 66, 163.
+
+  Sea-bottom, 18.
+
+  Sea-elephant, 132.
+
+  Sea-horse, 26.
+
+  Sea-lilies, 144.
+
+  Sea-lion, 132.
+
+  Sea-sawdust, 106.
+
+  Sea-urchin, 43.
+
+  Sea-weeds, 24, 106.
+
+  Seal, 130.
+
+  Serpula, 41.
+
+  Shells of Coral-reef, 65.
+
+  Ship-worm, 43.
+
+  Shrimps, 31.
+
+  Siphonophores, 95.
+
+  Skates, 36.
+
+  Slime glands of Fish, 165.
+
+  Sole, 37.
+
+  Solen, 35.
+
+  Sperm-whale, 127.
+
+  Spines in Plankton, 90.
+
+  Sponge, Hermit-crab and Worm, 150.
+
+  Star-fish, 44;
+    method of feeding of, 29.
+
+  Stenopus, 33.
+
+  Sting-ray, 36.
+
+  Stinging of Cœlenterates, 97.
+
+  Sun-fish, 122.
+
+  Swamp-fauna, 74.
+
+  Symbiosis, 146.
+
+
+  T.
+
+  Temperature of sea-water, 11.
+
+  Teredo, 43.
+
+  Thread-cells, 97.
+
+  Tides, 15.
+
+  Torpedo, 37.
+
+  Trepang, 153.
+
+  Trichodesmium, 106.
+
+  Tridacna, 65.
+
+  Trigger-fish, 63.
+
+  Tunicates, eye of, 30.
+
+
+  V.
+
+  Velella, 96.
+
+
+  W.
+
+  Walrus, 134.
+
+  Worm-tubes, 163.
+
+
+  X.
+
+  Xenophora, 162.
+
+
+  Y.
+
+  Yellow cells, 160.
+
+
+  Z.
+
+  Zoophytes, 30, 161.
+
+
+
+
+                              PRINTED BY
+                         TURNBULL AND SPEARS,
+                               EDINBURGH
+
+
+
+
+    “_A very useful series of small manuals on subjects of common
+                  interest._”--+Spectator.+
+
+
+                                  THE
+                      Library of Useful Stories.
+
+   _Small 8vo, cloth, price 1s. each Volume, post free 1s. 2d._
+
+            “_The more Science advances, the more it becomes
+              concentrated in little books._”--+Leibnitz.+
+
+
+                                  I.
+
+THE STORY OF THE STARS.
+
+  By +G. F. Chambers+, F.R.A.S., Author of “Handbook of Descriptive and
+  Practical Astronomy,” &c. With 24 Illustrations.
+
+“Mr Chambers writes in a vigorous and attractive style, and shows
+himself able to combine to an uncommon degree scientific accuracy
+of statement with a clear and attractive exposition. Beginners in
+astronomy who wish to acquaint themselves merely with the outlines of a
+noble science will find this volume of real service.”--_Speaker._
+
+“Told in a pleasing and attractive manner.”--_Athenæum._
+
+
+                                  II.
+
+THE STORY OF PRIMITIVE MAN.
+
+  By +Edward Clodd+, Author of “The Story of Creation,” &c. With 88
+  Illustrations.
+
+“It possesses the chief qualities that go to make a good book for the
+average man.”--_Nature._
+
+“Well printed, well bound, profusely illustrated, and in every
+respect capital material, on one of the most progressive of
+sciences.”--_Daily Chronicle._
+
+
+                                 III.
+
+THE STORY OF THE PLANTS.
+
+  By +Grant Allen+. With 49 Illustrations.
+
+“A brightly written, clear and accurate summary of the functions and
+habits of plants.”--_Daily Chronicle._
+
+“The whole book is excellent, but special praise is due to his
+exposition of the relations existing between plants and insects.
+Many chapters of the story he tells must prove to the uninitiated as
+exciting as a romance.”--_Aberdeen Free Press._
+
+
+                                  IV.
+
+THE STORY OF THE EARTH IN PAST AGES.
+
+  By +H. G. Seeley+, F.R.S., Professor of Geology, Geography, and
+  Mineralogy in King’s College, London. With 40 Illustrations.
+
+“A simple and popular summing up of the results that have been reached
+by geological science.”--_Scotsman._
+
+“Told plainly and pleasantly for a popular audience.”--_Bookman._
+
+
+                                  V.
+
+THE STORY OF THE SOLAR SYSTEM.
+
+  By +G. F. Chambers+, F.R.A.S. With 28 Illustrations.
+
+“His descriptions possess the double quality of simplicity and
+attractiveness.”--_Nature._
+
+“He repudiates the idea that unless a man can command a big telescope
+he is not in a position to do useful work in astronomy.... The little
+volume is an admirable example of science made easy without the
+sacrifice of strict accuracy of statement.”--_Speaker._
+
+
+                                  VI.
+
+THE STORY OF A PIECE OF COAL.
+
+  By +E. A. Martin+. With 38 Illustrations.
+
+“Treated with wonderful skill, simplicity, and
+thoroughness.”--_Bookseller._
+
+“Explains in simple and delightful fashion what coal is, whence it
+comes, and whither it goes, and in the concluding chapters shows how
+intimately it is connected with the interests of the botanist, the
+geologist, the physicist, the chemist, and the merchant.”--_Bradford
+Observer._
+
+
+                                 VII.
+
+THE STORY OF ELECTRICITY.
+
+  By +J. Munro+, Joint Author of “The Pocket-book of Electrical Rules
+  and Tables.” With 100 Illustrations.
+
+“Just the kind of book to give the general reader more correct views
+of the subject than many a pretentious tome.”--_The Electrical
+Engineer._
+
+“For general interest we must pronounce the little book without a peer,
+style and matter being alike excellent.”--_Glasgow Daily Mail._
+
+“A handy little book which has certainly the great merit of being up to
+date. We anticipate a large demand for the book.”--_Electricity._
+
+
+                                 VIII.
+
+THE STORY OF EXTINCT CIVILIZATIONS OF THE EAST.
+
+  By +R. E. Anderson+, M.A., contributor to Chambers’s Encyclopædia,
+  Encyclopædia Britannica, and Dictionary of National Biography, &c.
+  With Maps.
+
+“The author has performed a much needed service in a masterly
+manner.... We have nothing but praise for the work.”--_Literary
+World._
+
+“An admirable compendium of a department of knowledge which has been
+greatly advanced by the research of recent years.”--_Aberdeen Free
+Press._
+
+
+                                  IX.
+
+THE STORY OF THE CHEMICAL ELEMENTS.
+
+  By +M. M. Pattison Muir+, M. A., Fellow and Prælector in Chemistry of
+  Gonville and Caius College, Cambridge.
+
+“One of the most perfect popular introductions to science
+extant.”--_British Medical Journal._
+
+“Prof. Muir tells an enthralling story of the wonderful transformations
+of matter under the chemist’s magic wand. Ignoring formulæ he appeals
+in homely phrase to the imagination of the reader.”--_Knowledge._
+
+
+                                  X.
+
+THE STORY OF FOREST AND STREAM.
+
+  By +James Rodway+, F.L.S., Author of “In the Guiana Forest,” &c. With
+  about 27 Illustrations.
+
+“Contains a short description of a tropical forest, together with some
+elementary lessons which can be learned by studying the incessant
+struggle for existence of its varied flora.”--_Academy._
+
+“A noteworthy addition to the series in which it
+appears.”--_Scotsman._
+
+
+                                  XI.
+
+THE STORY OF THE WEATHER.
+
+  By +G. F. Chambers+, F.R.A.S., of the Inner Temple, Author of “Story
+  of the Stars,” &c. With 50 Illustrations.
+
+“An interesting volume about weather, and especially English weather,
+and presents facts, ideas, and suggestions which ordinary people will
+be glad to know.”--_St James’s Budget._
+
+“Shows how the weather forecasts are drawn up at the Meteorological
+Office, explains the construction and use of the various meteorological
+instruments, describes the nature and causes of such phenomena as
+the aurora borealis, and gives a collection of weather facts and
+signs.”--_Literary World._
+
+
+                                 XII.
+
+THE STORY OF THE EARTH’S ATMOSPHERE.
+
+  By +Douglas Archibald+, M.A., Fellow and sometime Vice-President of
+  the Royal Meteorological Society, London. With 44 Illustrations.
+
+“One of the best of the Story series that we have read ... the author
+is frequently able from his wide travels to illustrate his remarks
+from his own personal experience in climates where meteorological
+manifestations can be witnessed on a grander scale than in our own
+country.”--_Nature._
+
+
+                                 XIII.
+
+THE STORY OF GERM LIFE: +Bacteria+.
+
+  By +H. W. Conn+. With 34 Illustrations.
+
+
+                  _NEW VOLUMES IN PREPARATION._
+
+
+THE STORY OF THE POTTER.
+
+  By +C. F. Binns+, late of Worcester Royal Porcelain Works.
+
+
+THE STORY OF BRITISH COINAGE.
+
+  By +G. B. Rawlings+. With Illustrations from Coins in the British
+  Museum.
+
+
+THE STORY OF PHOTOGRAPHY.
+
+  By +A. T. Story+. With Illustrations.
+
+
+THE STORY OF RELIGIONS.
+
+  By +E. D. Price+, F.G.S. With Map, &c.
+
+
+THE STORY OF THE EARTH’S SURFACE.
+
+  By +H. G. Seeley+, F.R.S., Professor of Geology, Geography, and
+  Mineralogy in King’s College, London, Author of “The Story of the
+  Earth,” &c. With Illustrations.
+
+
+THE STORY OF ARCHITECTURE.
+
+  By +P. L. Waterhouse+, M.A., Associate of the Royal Institute of
+  British Architects. With Illustrations.
+
+
+THE STORY OF PAINTING.
+
+  By +A. G. Temple+, F.S.A. With Illustrations.
+
+
+       _To be followed by other Volumes, of which due notice
+                          will be given._
+
+                   *       *       *       *       *
+
+              LONDON: GEORGE NEWNES LIMITED, PUBLISHERS.
+
+*** END OF THE PROJECT GUTENBERG EBOOK 78328 ***