Elements of zoölogy

Front matter

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APPLETONS' SCIENCE TEXT-BOOKS

ELEMENTS OF ZOOLOGY.

Preface

In the present work, that is intended as a text-book for schools and academies of all grades, the design has been to present in concise and plain Ian. guage, and in the light of the latest research and investigation, the life-histories of the various groups that constitute the animal kingdom. Technical terms have only been employed where there was no simple equivalent, and the long tables of classification and formulae, that can only be understood after a complete mastery of biological knowledge, have been omitted, as tending to divert the attention of the student from the real issue. Professor Huxley strikes the key-note of this question when he says : " That the power of repeating a classification, with all its appropriate definitions, has anything to do with genuine knowledge, is one of the commonest and most mischievous delusions of both students and their examiners. The real business of the learner is to gain a true and vivid conception of the characteristics of what may be termed the nat-

Vlll

PREFACE.

necessary, and a carefully selected bibliography will be found following each principal group of animals. In the matter of illustration, representations of about five hundred animals and their parts have been given. Many of the cuts are original, and were designed especially to illustrate the habits of the animals, their economic value, etc. Others are from Buckley, Huxley, and various accurate sources already acknowledged.

The valuable assistance of S. U. Holder is cordially acknowledged, and thanks are returned to Mr. Ralph N. Monroe for photographs of the Florida crocodile and for the loan of valuable specimens ; also to Professor E. L. Youmans and Professor A. S. Bickmore for pertinent suggestions and advice. Acknowledgments are also made to Dr. E. P. Wright, of the University of Dublin, for the measurements of the gigantic shark Rhinodon ; and to W. Morey, Esq., of Colombo, Ceylon, for the original outline drawing.

C. F. H.

New York, November i, 1884.

Introduction

Definition of the Subject. — The science that treats of organic nature, or living things, is termed Biology. It is divided into Botany, that treats of plants ; and Zoology, that relates to animals.

The Cell. — All animals are made up of one or more cells, minute globules of a jelly-like substance called protoplasm, as a rule inclosed in a delicate covering or membrane. The protoplasm of genuine cells generally contains minute moving granules, and a round transparent body termed the nucleus, that contains a dark object, called the nucleolus. The lowest animals are single cells, and are termed unicellular, but in the higher forms the cells separate by self-division, and form two layers : outer {ectoderm), inner (endoderm), while a middle layer is called mesoderm. From these cell-layers bone and muscular tissue are formed, and the animals are said to be many-celled.

Difference between Animals and Plants. — It is not difficult to distinguish between the higher forms of animals and plants, The trees are sightless, have no locomotive organs, and, as a rule, live upon inorganic substances ; yet there are curious points of resemblance.

2 INTRODUCTION.

We know that a bird eats, moves, and breathes, and that its blood circulates ; but plants also eat, respire through their leaves, have a circulation of sap, and some are endowed with locomotive powers. When we descend to the lower forms of animal and vegetable life, the points of similarity become almost identical ; the swift-moving diatom so resembling some of the lowest animal forms that it is well-nigh impossible to distinguish between them. The plants, however, have no nervous system, no special organs of circulation or digestion that characterize the majority of animal forms, so that an animal differs mainly from a plant in possessing, as a rule, a nervous system and special organs of circulation and digestion.

Classification. — The animal kingdom, that is estimated to contain one fourth of a million species, is separated into two primary divisions : the Protozoa, or single-celled animals, and the Metazoa, or those composed of many cells. The latter are separated into eight branches : Porifera, Coelenterata, Echinodermata, Vermes, Mollusca, Arthropoda, Timicata, Vertebrata. These are in turn divided until the varied forms are grouped, like with like. This end is attained by comparison, and the result is termed classification. Thus the dog, as distinguished from a plant, is placed primarily in the animal kingdom. Possessing a backbone, it is placed in the branch of vertebrate animals. It differs from the fishes, reptiles, and birds, by giving milk ; hence it is placed in the class of mammals. Continuing our comparisons, we find that, with the lions, tigers, and cats, it is a flesh- eater, and so is placed in the order carnivora. From its general appearance and form, it is associated with others in the family of dogs. With others that have a similar structure, it is given the generic name canis ; then, to distinguish what kind of a dog it is, wild or domestic, it is given a specific or specifying name, as the common

INTRODUCTION. 3

dog, Canis vulgaris. Hence we have the following classification :

DOG.

Kingdom : of Animals.

Branch : Backboned, Vertebrates.

Class : Milk-givers, Mammalia.

Order : Flesh-eaters, Carnivora,

Family : Dogs, Canidse.

Genus : Dog, Canis.

Species: Canis vulgaris.

Variety : Newfoundland.

Chapter I. First Branch Of Animals

PROTOZOANS (First Animals).

General Characteristics. — The Protozoans are one-celled animals, in this differing from all others. The lowest forms resemble microscopic bits of the white of an egg. They have no definite shape, and move by a bulging out of the body-mass into root-like projections called pseudopodia, or false feet. In the interior are minute granules that move about (circulate), and in all, except the lowest protozoans, is seen a central oval body called the nucleus, and a hollow, transparent space, that contracts and enlarges with some regularity, called the "contractile vesicle." The higher forms have silicious or calcareous shells "and permanent organs.

Class I. — MONERS.

These are shapeless bits of transparent matter (Fig. i) containing merely circulating granules. By extending the body into pseudopodia, or false feet, and contracting them, they glide slowly along. Their prey is seized by surrounding it with the false feet, which fuse about it, and the victim is absorbed into the body-mass. They reproduce by simple division, or as in Fig. i. The Moner assumes a thick covering (becomes encysted), a, divides into spheres., b, that burst out, c, d, e, and soon assume the parent form,/

Fig. i. — Protomyxa aurantiaca. f, eating ; a and d, encysting ; c, developing into monad-like young.

Class II. — Rhizopoda {Animals with Root-like Feet).

General Characteristics. — Animals resembling the moners, but with a distinct outer and inner portion, the latter containing, as well as granules, several nuclei

PROTOZOANS.

Fig. 2. — a, Amoeba throwing out pseudopodia ; d, encysted.

and contractile vesicles. They are either naked or shelled.

Order I. Foraminifera {Hole- Bearers). — In the simplest form, the Amoeba (Fig. 2), the body is divided into a

transparent outer covering, and an interior portion containing the nuclei,and circulating granules that appear to be kept in motion by the pulsation of the contracting vesicle. It moves along by throwing out pseudopodia, or false feet, and ingulfs its food — desmids, diatoms, and other minute forms— as does the moner. The Amoeba reproduces by simple division.

Shelled Amoebae. — These forms (Fig. 3) secrete rich calcareous or horny chambered shells, from which are thrown out the false feet, extending in every direction in search of prey, and fusing about it without the shell. They are generally minute, but one found off Borneo measures two inches across. They reproduce in different ways ; in one, the young resemble monads (Fig. 6), finally assuming the parent form.

Order II. Radiolaria (Rayed Animals). — In these

animals (Fig. 4) the false feet are generally pointed, and the shells, which are formed of silica, not lime, are richly ornamented with spicules, or rays, and perforated with openings for the pseudopodia, that secure their food, as we have seen in the Foraminifera. They reproduce by di-

Fig. 3.

-Rotalia, with extended pseudopodia.

GREGARINIDA.— INFUSORIA.

Fig.

vision within the shell, the young at first resembling little oval bodies, with hair-like tails.

Value. — The shells of the marine forms fall in a shower upon the bottom, and form chalk-beds, as the Dover cliffs, in England, thus adding to the land of the globe. The stone of the Pyramids is made up of fossil Foraminifera.

Specimens for Study. — The Amoebce, can be found on leaves in fresh-water

ponds. Foraminifera can be caught with a fine net in the ocean, or found in pools at low tide. The shells can be ground and mounted for the microscope.

Class III. — GREGARINIDA.

General Characteristics. — These (Fig. 5) are minute forms that take up their abode in lobsters, crabs, beetles, cockroaches, worms, and other animals, and lead a parasitic life, existing upon the juices of the animals they inhabit.

They resemble minute worms ; one, found in the European lobster, half an inch in length, is called Gregarina gigantea, being the largest single-celled animal known. They undergo several curious changes before reaching mature growth.

Fig. 5. — Gregarina of Nemertes Gesseriensi's, showing- nucleus and granu les .

Class IV. — Infusoria.

General Characteristics. — Animals of permanent forms with cilia, or hair-like organs, for locomotion and procuring food. They are either free or stalked.

PROTOZOANS.

Order I. Flagellata (Monads). — If standing water is examined with a microscope, it will be found fairly alive with numbers of minute pear- and oval-shaped creatures,

having, at the place where the stem would be, alash, that vibrates and whirls about as the animal moves along. One of. the Monads, the Noctiluca (Fig. 6), a giant of its kind, lives in the ocean, and in appearance resembles a currant about the size of a small pin-head.

On one side there is a groove, from which issues a single whip, or cilium, that is a locomotive organ, and near where this joins the body is the mouth. The outer surface of the animal is a firm membrane, beneath which is the jelly-like mass containing numerous granules, from which rises a regular network of fibers that lead over the entire body. The young are produced by a mere breaking off of a portion of the parent.

Fig. 6. — Giant monad Noctiluca. e, gastric vacuole ; g, radiating filaments.

Note. — As many as thirty thousand of these forms have been seen in the ocean in a cubic inch, moving about with great rapidity, and producing a most wonderful phosphorescent light.

Other monads are compound (several joined together), as the Uvella, while others are fixed, attached to the bottom by a slender stalk, as the Codosiga. Here the little hair-like organ is used to throw food into the mouth. Others of this order have their delicate forms protected by a hard

INFUSORIA.

Fig. 7.

Acienttz. I 7 , attached by stalk ; G, encysted.

shell, have one or several whips, or lashes, and a row of cilia, with which they lash themselves along with great velocity.

Order II. Suctoria. — This order is represented by the Acienta (Fig. 7), beautiful, trumpet-like animals resembling the purest glass.

From the body project numerous slender tufts that are not cilia, but hollow tentacles (arms), having in some a sucker at their ends. Their prey is grasped by the arms, that contract, each at the same time sinking into the body of the victim,

pumping or sucking out its juices. They multiply by self-division, while some species have free-swimming young.

Order III. Ciliata. — These are the true Infusorians, easily observed with a common microscope, a drop of standing water furnishing myriads. They are either free and covered with cilia, or stalked, with the cilia about the head. They have a mouth, a digestive cavity, or stomach, and multiply by self-division or budding. Among the free swimmers, the Paramecium (Fig. 8) are the giants, and easily observed if a little carmine is introduced into the drop. As they dart about, we see that they are oblong, narrowing at the head, the back rising into quite an elevation, beneath which, upon the under side, is the mouth. From the head and on all sides are minute prolongations of the body, or cilia, arranged in rows, organs of locomotion. The Vorticellce, (Fig. 9), or bell animalcules, are bell-shaped, and held by a long, slender, glass-like stalk, by which they contract. A colony of them presents a curious sight ; the bells are continually contracting, as if jerked from behind, the stalk forming a

IO

PROTOZOANS.

perfect screw in the operation. They multiply by a simple division (Fig. 9, c) or by budding (d, d).

FlG. 8. — Paramecium dursaria, showing cilia, c, contractile vacuole ; d, food.

Fig. 9. — Vorticellce. a, extended ; fr, coiled ; c, division ; d, d, free-swimming buds.

Works on Protozoans for further reference,

" The Atlantic, and Depths of the Sea," Sir Wyvillc Thomson ; Carpenter " On the Microscope " ; " Mind in Nature," H. J. Clark ; Leidy's " Fresh-Water Rhizopods" ; Pritchard's "Infusoria" ; " Manual of Invertebrates," T. H. Huxley ; " Challenger Reports " ; " Evenings at the Microscope," Gosse ; Thompson's " Monthly Microscopical Journal "; "The Quarterly Microscopical Journal"; Bastian's "Origin of Lowest Organisms, and Beginnings of Life " ; " Notices of Protozoa," by Professor Leidy, in " Proceedings of Philadelphia Academy of Natural Sciences " ; " Water turned to Blood by Red Infusoria," in " Popular Science Monthly," vol. iv, p. 202.

Chapter II. Second Branch Of Animals

SPONGES (Porifera, pore-bearing).

General Characteristics. — The sponges were for many years considered plants, but now they are known to be many-celled animals. In the Ascctta (Fig. 10), we have a vase-shaped cylinder, /, composed of cells arranged in three layers. In the second or middle layer is developed a network of objects of silex or lime, called spicules (Fig. it), that form the skeleton, and support the cellular, jelly-like mass. The walls of the vase are everywhere perforated with pores, J>, through which water passes, carrying food.

The cells of the inner layer are provided with a cilium, or lash, 777, and, taken individually,

resemble monads. As food floats by, each cilium throws the minute bits against its cell ; the soft portion is absorbed, the harder parts being rejected, and, wafted along by the cilia, find egress at the single large opening, O. In this

Fig. ii.

-Spicules of flint-sponges, highly magnified.

SPONGES.

Fig. io. — Ascetta primordialis. I. o, exhalent opening ; p, inhalent pores ; g, ova. Star-like spicules are seen on the outside. II. Section showing pores (p), with cilia of the cells extending into them. III. Cell showing lash, or cilium. IV. Same, with lash retracted. V. Embryo of Ascetta mirabilis. VI. Section of embryo.

LIME-SPONGES.- CARNEOSPONGI^.

way the Ascetta feeds. Other sponges differ from it in having a shapeless form, many large outlets instead of one, and numerous sacs lined with ciliated cells.

Development. — The young are at first free swimmers, being produced from eggs, escaping into the water as oblong little creatures, with numerous cilia, V. They soon become attached to the bottom, spicules appear, and they gradually assume the parent form.

Order I. Lime-Sponges (Calcispongioe). — In these, the spicules are made of lime, and the canals lined with ciliated cells. They are few in number, and may be represented by the little white sponge, Sycon ciliatum, common in the sea-weed of the Eastern Shore.

Order II. Carneospongiae. — The spicules of these forms are either fibrous and horny, or silicious, and the ciliated cells are only found in little cavities, or stomachs. To this order belong a host of beautiful forms : the common sponges of commerce, the fresh-water Spongilla,

the wondrous Holtenia, and the Eupleciella, or Venus's flower-basket (Fig. 12).

-Skeleton of Euplectella speciosa.

SPONGES.

Value of Sponges. — There are six species of sponges valued in commerce ; three are found in America, in Key West and the Bahamas, the others coming from the Mediterranean and Red Seas. Nearly all the flints are the remains of ancient sponges.

Specimens for Study. — Sponges are difficult to keep in the aquarium. In our Northern fresh-water ponds, the Siphydora is common, and, in streams, the Spongi/la, while various kinds can be found along the coast. In default of living specimens, the common toilet-sponge should be used, and sections made with a razor for examination under the microscope.

Works on Sponges for further reference.

" The Glass Sponges," by Rev. Samuel Lockwood, in " Popular Science Monthly," vol. iii, p. 529 ; "The Common Fresh- Water Sponge, Spongilla" by Professor W. C. Williamson, in " Popular Science Review," January, 1868 ; " North American Poriferse," by A. Hyatt, in "Memoirs of Boston Society of Natural History"; "Life Histories of Animals," by A. S. Packard, Jr. ; " The Atlantic, and Depths of the Sea," Sir Wyville Thomson.

A Syrian sponger.

Chapter III. Third Branch Of Animals

HYDROIDS, Etc. {Ccelenterata, hollow intestine).

General Characteristics. — A simple sac, as the Hydra, composed of two-cell layers, possessing a stomach, or digestive cavity. The mouth is encircled by tentacles, which are hollow, and connect with the stomach.

Class I. — Hydrozoa.

Order I. Hydroids. — One of the commonest animals of the aquarium, if the water is taken from the brook or stream, is the Hydra (Fig. 13)— a simple, elongated stomach one quarter of an inch in length, ending in a mouth that is surrounded by from five to eight tentacles that are extensions of the body, hollow, and connecting with it.

If examined closely, myriads of small cells will be seen, many of which contain delicate threads or darts, called lassoes, that are thrown out as weapons of defense (Fig. 14). By cutting a Hydra

Fig. 13. — Fresh-water Hydra viridis. 1.

Long-armed Hydra feeding on small animals, a. 2. Hydra fusca throwing off young Hydra-buds.

l6 LIME-SECRETING HYDRO IDS.

into sections, each will soon produce a crown of tentacles, and grow into a perfect animal. The Hydra can be turned inside out, and within an hour recover its natural

Fig. 14.— Lasso-cells of Hydra. 1. Arm of Hydra, containing cells. 2. Cell magnified. 3. Cell after bursting open.

position ; more marvelous yet, if when so treated it is spitted with a pin or needle so that it can not turn, it will eat and reproduce its kind as if nothing had occurred. Some are solitary, while others live in colonies. They reproduce by budding (Fig. 13, b, b) and by eggs.

Lime-secreting Hydroids {Millepord). — Some of the Hydroids secrete lime. They resemble true corals in appearance, and were long considered as such. Under the microscope, it will be seen that the lime secreted is tunneled by numerous canals which in life are filled by the animal. The polyps are of two kinds, and, in a millepore found at Tahiti, they are in groups, the largest being stout polyps, with four tentacles, a stomach, and mouth ; but the polyps about it, rising from the smaller pores, have no mouth or stomach, but many tentacles, whose duty is to capture food for the short, thick-set polyp between them. Some of the Hydroids, instead of bearing young like themselves, produce perfect jelly-fishes {Medusoe) ; such is the Campanularia (Fig. 15), that throws off, by budding, a free jelly-fish (3), that in turn produces eggs that become, not jelly-fishes, but fixed Hydroids (1). This is called alternate generation. The free-swimming young are often brilliantly luminous, presenting a wondrous appearance on dark nights.

DISCOPHORA.

The Monocaulus is a gigantic Hydroid, seven feet high, and nine inches across the expanded tentacles, living in the Atlantic at a depth of four miles below the surface. Many of the so-called mosses that are common on the shore, and are pressed as sea- weed, are in reality compound Hydroids enclosed in horny cells, as the Sertularia.

Fig 15.— Campanularia. 1. Natural size. 2. Animal magnified : S, sac containing jelly-bell ; a a, animal feeding. 3. Free-swimming young, magnified. 3', natural size of jelly-bell.

Order II. Discophora— We now come to jelly-fishes that are developed directly from eggs, as Pelagia campanella, or, as in Aurelia, produced from a Hydra form (Fig. 17, 1). They vary in size, from the little Lucernaria that attaches itself to weeds by a sucking disk, to the gigantic Cyanea, that is from two to seven feet in diameter, with tentacles over one hundred feet m length.

i8

HYDRO IDS, ETC.

These jellies are disk-shaped, the tentacles in Cyanea hanging in eight distinct bunches from the margin, and armed with darts or lasso-cells, that form terrible

Fig. 16.— Adult Aurelia, showing the water-vascular canals.

weapons of defense. Around the fringed margin are eight protected eyes. The mouth - opening is square, leading into a large stomach, from which radiate four branching tubes (Fig. 16) called water-vascular canals.

They form a network at the edge, and connect with a tube that encircles the margin of the disk. Through these branches digested food and water circulates, or finds its way over the body. A somewhat similar arrangement is found in all jelly-fishes. In swimming, the disk contracts „ _ r A and expands in regular time,

Fig. 17. — Development of Au- r .

reiia. 1. Early stage. 2. averaging twelve or fifteen times

Jelly-fish ready to break off. a minute.

FRESH- WA TER JELL Y -FISHES.

Note.— In specimens of Aurelia, 95.84 per cent of the animal is water ; the solid matter in any jelly-fish is rarely over five per cent of the whole.

Fresh-Water Jelly-Fishes— These have recently been discovered in England. They are one third of an

FlG. 18. — A jelly-fish swimming {Pelagid).

inch in diameter, and probably come from some warm climate, as they are only active when the temperature of the water is about 85 .

COMPOUND HYDRO IDS,

Developme?it of Discophora. — They multiply by eggs that are deposited in the autumn, and are at first spherical, quickly changing to a pear-shape, and attaching themselves to rocks or weed. Now, tentacles appear (Fig. 17, 1), varying in number from eight to twenty-four, and after eighteen months the pear divides off into disks until we have a pile of scalloped saucers one upon another (2). The highest one dies, while all the rest break off and swim away, little jelly-fishes, that in time grow into the gigantic Cyanea or others, as the case may be.

Value. — They form the food of some whales and fishes.

Note. — The gigantic Cyanea affords a home under its curtains for numbers of fishes and several crustaceans, while in its mouth-folds lives a long, tapering sea-anemone {Bicidium parasiticum), that in many cases mimics in color that of its protector.

Order III. Siphonopho-

ra. — These are the most beautiful of the Hydroids, and are rarely seen in the North.

They are free-swimming colonies. The Portuguese mano'-war, or Physalia (Fig. 19), is a mere bubble, seemingly of the finest satin, that floats upon the surface. From the upper portion rises at will a fluted membrane, colored with delicate tints of pink, that is used as a sail ; from the low-

Fig. 19. — Portuguese man-o'-war, Physalia Arethusa.

SEA-ANEMONES AND CORAL POLYPS. 21

er portion extends a mass of tentacles of the richest blue, and, from their armament of lasso-cells, of the most dangerous character. They are called Zooids, and are of four kinds. Some aid in locomotion, some are reproductive, while others are feeders for the entire colony. The tentacles are dragged from twenty to one hundred feet or more behind. The beautiful filaments form tempting baits when lowered, and in this way the Physalia feeds. The man-o'-war generally has several tenders, little fishes of the genus Scombridce, of the exact color of the deathdealing tentacles, that live under and among them, a wonderful case of mimicry.*

Allied to the Physalia are the Porpita and Velella. The latter also floats upon the surface, a raft bearing a silvery sail, while beneath is the same rich coloring of the Physalia.

Works on Hydroids for further reference.

" Acalephs ( Jelly-Fishes) of North America, with Pictures of most of the Species in Catalogue of Museum of Comparative Zoology," by A. Agassiz ; L. Agassiz, " Contributions to the Natural History of the United States," vol. iv ; " Sea-side Studies in Natural History," Agassiz ; " Sertularian Zoophytes of the Coast of England," T. Hincks; "Popular Science Review," 1878, p. 223; Huxley's "Manual of Invertebrates" ; "Challenger Reports."

Class II.— Sea-Anemones and Coral Polyps {Actinozod).

General Characteristics. — These are well represented by the sea-anemone, or Actinia (Fig. 20). In appearance

* The author once swam over the tentacles of a Physalia with an almost fatal result ; the blue marks were plainly visible six or eight months after. These fishes not only mimic the color of the tentacles, but assume vertical positions, so that they seem actually a part of them. I have often lifted the man-o'-war, which can be safely done by the " sail," and the fishes that were previously unnoticed would dart about in the greatest alarm. A more remarkable case of protective mimicry is not known.

HYDROIDS, ETC.

they resemble cylinders attached to the bottom, the opposite end containing the mouth, which is surrounded by numbers of hollow tentacles, armed with lasso-cells (Fig. 21), while near the base of the tentacles are the minute

Fig. 21. — Lasso-cell of an anemone.

Fig. 20. — Anemone with tentacles expanded, attached by sucking disc to the bottom.

Fig. 22. — Cross-section of anemone, showing septa.

eye-spots. If a dead anemone that has become somewhat hardened is cut open vertically, we first notice the stomach, that, divided into mouth and stomach proper, seems suspended in the body, held in place by six partitions (Mesenteries) (Fig. 22), that divide it into as many sections, which are again divided by others. Each of the six principal partitions is perforated with an opening, and the chambers connect with the tentacles, so that water, and food captured by the tentacles, is taken in at the mouth, and penetrates, by the opening at the bottom of the stomach, to every part of the animal.

The anemones vary greatly in size, from delicate unattached forms that live up among the folds of the great jelly-fish Cyanea to enormous ones two feet across. The

CORAL-MAKING POLYPS.

Cerianthus of the Philippine Islands, with its thread-cells, builds a sheath or leathery tube one foot four inches in length, that is sunk into the mud.

Developvient. — Anemones multiply by budding, or, if pieces of the disk are cut or torn off, they will grow into anemones. They also deposit eggs, the young being at first free swimmers, by means of cilia, finally becoming fixed upon the bottom, and assuming the adult form.

Note. — In their habits they are remarkable. One observed by Dr. Collingwood in the China Sea was two feet in diameter, giving shelter in its stomach to a little fish, that, when danger approached, rushed into its protector, whose tentacles closed up like a door. A fish, known as Premnas biaculeatus, also lives within the stomach of the anemone, Actinia crassicornis. Some live a roving life, like the Adamsia, that is often found upon the back of the hermit-crab, that, upon leaving its shell, obliges its friend, the anemone, to change also. The Urticina is luminous.

Value. — The anemones are great purifiers, and are eaten in various parts of the world.

Coral-making Polyps. — The coral animal may be considered an anemone that has the power of secreting lime. In the star-coral (Astrea), the young is seen at the end of June — a little oblong-shaped body, swimming about by its cilia, or oars. It soon attaches itself to the bottom, and, if in a few days it should be removed, there would be found a little platform with radiating partitions of lime alternating with the soft ones that we have seen in the anemone. If allowed to grow, tentacles soon appear ; other small partitions are now secreted, that extend to the outer wall, which is also being secreted ; and, finally, we have a coral polyp, from which others branch, until large blocks are formed of many individuals, but all connected. So it will be seen that the coral is not an insect, neither does it erect or build its house any more than a man builds his skeleton, but is a lime-secreting animal, pure and simple.

24 DEEP-WATER CORALS. .

The corals that we are familiar with have been bleached, but when taken from the water they are of various shades of olive and brown.

Single-Polyp Corals. — The Fungia, or Mushroom- Coral, often attains a length of twelve inches, and is a single polyp, in which the radiating septa are plainly seen. They are the commonest forms of the greater depths ; ten genera live in water a mile deep, four at nearly two miles, while the Fungia symmetrica has been found in from one hundred and eighty feet to three and a half miles of water. The Caryophyllia is a common form in the Mediterranean. Some are luminous.

Branch-Coral (Madreporidce). — The Branch or Tree Coral of Florida (Fig. 23) is a familiar example, and the w m an

8SS0BP

.

Fig. 23. — Madrepore. Dead and living branch.

sides of deep channels in the reef bristle with it, the coral growing in perpendicular walls and covering the reef in vast patches, affording protection to myriads of animals. The Leaf-Coral spreads out in great leaves several feet in width. The Branch-Corals grow seven or eight inches a year, contrary to general belief.