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The next group of animals is a large one, comprising the various kinds of Cuttle-fishes and the Pearly Nautilus, all of which live in the sea. The name of the group is Cephalopoda (from the Greek, kephale, head, and podes, feet), so called because the head is surrounded by a series of "arms," or muscular processes which the animal uses for walking with at the bottom of the sea. As the representative of these animals we shall select the common Calamary (Loligo vulgaris) of British seas. This singular creature (fig. 31, A) grows to a length of from a foot and a half to two feet, and is not uncommonly found stranded on the shore after heavy storms. The animal consists, as can readily be seen, of two portions—an anterior or front portion, carrying the eyes, and a posterior or hinder portion, into which the former is loosely fitted in front. The hinder portion is the body proper, and is of a cylindrical or rounded shape, furnished behind with a broad triangular fin on each side. These fins give the hinder end of the body a somewhat lozenge-shaped form, and they enable the animal to swim with great power and rapidity. The whole of the body is enclosed in thick leathery skin, of a bluish colour, and covered with numerous purplish-red specks and blotches. The under surface is of a lighter tint, and the animal can change its colour at will, and can thus adapt itself to the colour of surrounding objects.
The anterior portion of the body carries on its sides a pair of large, conspicuous, globular eyes, and bears in front a circle of muscular processes or "arms." These arms are ten in number, eight of them of equal size, and the remaining two very much longer than the others. The eight short arms (fig. 31, A, a) are furnished on their inner surfaces with two rows of little cups, or "suckers," which enable the animal to seize objects firmly, and also to walk about head downwards at the bottom of
Fig. 31.—A, The common Calamary (Loligo vulgaris), reduced In size: a One of the ordinary wins; ( One of the longer arms or " tentacles" B, Skeleton or "pen" of the same, one fourth natural size (after Woodward). C, Side view of one of the suckers, showing the horny hooks surrounding the margin. D, View of the head from in front, showing the bases of the arms (a) and tentacles ((), the mouth (in), and the funnel (/).
the sea. These suckers, numerous as they are, are entirely under the control of the animal; and each is furnished with a ring of horny hooks round its margin (fig. 31, C, so that they constitute collectively a most efficient apparatus for adhesion and for grasping purposes. The two longer arms are known as the "tentacles" (fig. 31, A, t), and they only carry suckers at their extremities, which are expanded and club-shaped.
If we separate the arms a little from one another, so as to expose the front of the head, we see the opening of the mouth, surrounded by the bases of the arms (fig. 31, D, m); and within the mouth is a pair of strong jaws, of a horny consistency, brown with white tips, and very like the beak of a parrot, except that the undermost jaw is the longest.
The only other point in the external anatomy of the animal which needs mention, is a peculiar tube which is seen on the under surface of the head. (This is not visible in fig. 31, A, since this represents the upper surface of the animai, but it is shown in fig. 31, D, /). This tube is called the " funnel," and the animal has the power of ejecting through it a stream or jet of water. By means of this jet, by its reaction on the surrounding water, the animal can propel itself, tail foremost, without the necessity of using its fins. The "funnel" also serves other purposes which will appear hereafter.
Returning now to the mouth, we may briefly examine the internal structure of the animal. The mouth, with its beak-like jaws, opens into a gullet, surrounding which we find a ring of nervous matter (fig. 32, n), which represents the brain of the higher animals, and which is protected by a rudimentary skull. Besides the jaws, the mouth also contains a tongue, the hinder portion of which is covered with spines. Thfe gullet leads into a stomach, from which proceeds an intestine, terminating at the bottom of the "funnel." The funnel, therefore, serves to convey out of the body the undigested portions of the food. There is also a well-developed liver (fig. 32, I), which pours its secretion into the intestine. Placed upon one side of the intestine is a curious organ, which is generally known as the "ink-sac" (fig. 32, i). This is a little bag or membranous sac, filled with a jet-black semi-fluid material—the "ink" —which the animal has the power of squirting out at will. The tube which leads from the ink-sac opens at the base of the funnel, and the "ink" can thus be thrown into the water outside. The animal accordingly, when threatened by any danger, emits a jet of this inky fluid, and makes its escape under cover of the cloud which it has thus raised.
The remaining internal organs which mainly concern us, are the heart and gills. The heart receives the pure blood, which has ed through the gills, and distributes it to all parts of the body. The gills are the breathing-organs, and are two in number. They are pyramidal in shape, and the impure or venous blood is submitted in them to the action of the oxygen contained in the water, which is freely admitted to them; and which, after passing over their surface, is again expelled from the funnel.
Lastly, we find that the soft and yielding body of the Calamary is strengthened and supported by a singular
rig. 32.—Diagram of the internal anatomy of a Cuttle-fish (altered from Huxley), m Jaws n Nervous ring surrounding the gullet; p Intestine, opening at the base of the funnel (/); i Ink-sac, also opening at the base of the funnel; g Gills; s Skeleton.
internal skeleton, which is enclosed within the thick skin of the body. This skeleton (fig. 31, B) has something of the form of a paddle or of a feather, and it is generallyknown as the "pen." It is of a horny consistence, semitransparent, and consisting of a central stem with two lateral expansions or "wings." In old specimens there are several of these "pens," packed closely one behind the other.
The Calamary, as before mentioned, lives in the sea, and the present species is generally distributed round the shores of Great Britain. Where abundant, it is used by the fishermen as bait. In the quaint language of Pennant, these animals "inhabit all our seas; are gregarious; swift in their motions; take their prey by means of their arms, and embracing it, bring it to their central mouth. Adhere to rocks, when they wish to be quiescent, by means of the concave discs that are placed along their arms." They appear to live upon shell-fish, and sometimes sea-weed, and they lay their eggs in clusters containing many thousands.
Recapitulation Of Essential Characters.—Of the above-mentioned characters which distinguish the Calamary, the following are essential: The body is symmetrically constructed, so that you could divide the animal with a knife into two halves, which would externally be exactly similar to one another. The mouth is placed in the front of the head, and is surrounded by a circle of muscular processes or "arms." The breathing-organs are in the form of gills; and the water which has passed over the gills is expelled from the body by means of a muscular tube or "funnel." By the jet of water thus emitted, the animal can propel itself through the water. The mouth is furnished with beak-like jaws, and also with a tongue, the hinder part of which is provided with bent spines. The nervous system is highly developed, and is partially protected by what may be regarded as a rudimentary skull. These characters distinguish all the animals which are related to the Calamary, and they may therefore be taken as the distinctive characters of the entire class of the Cephalopoda.