DOG-FISH; SAW-FISH.

61

eggs, which are enclosed in flat oblong cases, with a long tendril from each corner, by which it clings to solid bodies, or to seaweed. In these cases, which are commonly known by the name

of "fairies' purses," there is a fissure at each end, which admits the free access of sea-water to the egg; and through one of these the young subsequently escapes. The Small Spotted Dog-fish is the species most common on our own shores; and it is not only very troublesome to the fishermen by entangling itself in their nets, but also by frightening away the shoals of Herrings, &c., which are migrating towards the coast.-The last fish of this family here to be noticed, is the Pristis or Saw-fish; so named

FIG. 284.-SAW-FISH.

from the extension of its snout into a long flat blade, furnished with a row of sharp spines, resembling teeth, on either side. With this formidable weapon the Saw-fish attacks the largest Whales, and inflicts very severe wounds. It sometimes attains

62

RAIDE;-STING-RAY, THORNBACK.

the length of twelve or even fifteen feet. This fish is very widely distributed, being found in the arctic, antarctic, and tropical seas; but it seldom approaches the shore.

584. The true Rays, typical of the family RAIDE, have the body so flattened, that the pectoral fins seem like a continuation of it; and these meet in front of the snout, and are prolonged backwards as far as the ventral fins; thus giving to the whole body a nearly circular form. The eyes are situated on the upper side of the body, as in the Flat-fish (§ 564); but it will be observed, that the plan of construction of the Rays and Skates, is entirely different from theirs, the two margins being here composed of the edges of the pectoral fins, whilst in the Flat-fish they are formed by the dorsal and anal; and the Flat-fish habitually lying on one side, whilst the Rays, &c., lie on the abdominal surface, where we find their mouth and gill-openings. These fish live for the most part near the bottom of the water, on beds of sand or mud. When disturbed, they glide along in an undulating manner, with a slight motion of the pectoral fins ; and if attacked, they defend themselves by lashing violently with the tail, which is often furnished with sharp spines. In the

Sting-Ray (Trygon), the tail has a single strong spine, notched on both sides. There are several species, intermediate in form between the Sharks and Rays, by which the two families are connected. Most of the family are extremely voracious, feeding on Fishes and Crustacea, and on naked or testaceous Mollusks. The teeth are flattened and lozengeshaped; and so powerful are the jaws, that they are capable of crushing the shell of a Crab with the greatest ease. Some of the Rays produce their young alive; in those which lay eggs, these are deposited in a horny case, like that of the Dog-fish. One of the most common of the British species is the Thornback; so named from the skin of its back being covered with thorny tubercles, variable in their number; this fish is taken in abundance in the spring and summer, when it visits the shallows for the deposition of its

FIG. 285.-STING-RAY.

TORPEDO.-CYCLOSTOMATA; LAMPREY.

63

eggs, and it is an excellent article of food. The Torpedo, or Electric Ray ($ 542), is occasionally met with on the Channelcoast of England; but it is more common in warmer seas, especially the Mediterranean. It is peculiar, not only from the possession of the electric apparatus, but also on account of the fiddle-shaped form of its body (Fig. 263). The Myliobates receives its common name of Sea-eagle, from having the pectoral fins of extreme breadth, so that it much resembles a bird of prey, with its wings expanded. It inhabits the depths of the ocean, and attains a very large size; in a specimen caught in the West Indian seas, the length of the body was 10 feet, its greatest breadth 13 feet, and the length of the tail 15 feet.

ORDER IX.-CYCLOSTOMATA.

585. The Fishes of this Order are the least perfect of the whole class, in regard to the construction of their skeleton; and are, therefore, at the bottom of the whole series of Vertebrated animals; which they may be correctly regarded as connecting with the Invertebrated sub-kingdoms. So far are they from having a jointed vertebral column, that this is replaced, in the highest among them, by a sort of cylinder of cartilage, which represents the bodies of the vertebræ, but which does not show any definite division into segments; and in the lowest, this cylinder has not even the firmness of cartilage, but consists of a membranous bag, containing a gelatinous semi-fluid substance. There are no ribs, nor are there either pectoral or ventral fins; there is, in some, however, a kind of fin beneath the tail, but this has no rays. The body is usually prolonged, and nearly cylindrical; and terminated by a circular mouth adapted for sucking. In the Lampreys there are seven gill-openings on each side; there are strong teeth in the ring formed by the pair of jaws; and the inner part of the disc, which may be considered as the lip, is also beset with hard tooth-like tubercles. The tongue, which moves backwards and forwards like a piston, and which is the principal instrument in the act of suction, is also furnished

64

LAMPREY, HAG, LANCELOT.

with two longitudinal rows of small teeth. By means of this sucker, the Lamprey can attach itself to the bodies of the largest

FIG. 286.-LAMPREY.

fishes; and is able speedily to pierce through their integuments, and to prey upon their substance. The largest species, which attain the length of two or three feet, are marine; the former, which chiefly inhabit rivers, are sometimes called Lamperns. The members of the genus Myxine, or Hag, and its allies, have not even a cartilaginous ring around the mouth, its borders being entirely membranous, and furnished with only one tooth. The mouth is surrounded by eight cirrhi, or tendril-like feelers; which remind us of the arms of the Cuttle-fish in miniature. This fish is destitute of eyes; and does not seem, indeed, to have any other special organ of sensation than these cirrhi. The best known species is known to British fishermen under the name of the Hag; it is found in the interior of other fishes, whose bodies it has entered for the purpose of devouring them; and it seems to attack in preference those which have been hooked, and which, consequently, are not able to defend themselves. As many as six Hags have been found in the skin of a single Haddock, on the Norway coast (where this species is more abundant than our own), the flesh of which they had almost entirely consumed. It is usually from twelve to fifteen inches in length, and of the thickness of the little finger; and its whole tissues are so soft, that it would not have been supposed capable of inflicting any serious injury. The quantity of mucus which it can secrete from its surface is enormous; it has been asserted, that if a Hag be placed in a pitcher of sea-water, it will speedily convert this into a semi-transparent jelly; and that, if placed in a fresh quantity of water, it will change this in the same manner. The most imperfectly formed of all Fish is, probably, the Amphioxus, or Lancelot; which has, by many Natu

LANCELOT.-GEOLOGICAL DISTRIBUTION OF FISHES.

65

ralists, been removed altogether from the Vertebrated sub-kingdom, on account of the almost complete absence of what are usually regarded as the distinguishing peculiarities of that group. Nevertheless, an attentive examination of its structure shows, that it bears a closer resemblance to the true Fishes than to any other animals-exhibiting their conformation in (as it were) a degraded form. It is of very diminutive size, scarcely an inch in length, very slender, and almost transparent. The body is compressed laterally; and there are no pectoral, ventral, anal, or caudal fins, but only a single dorsal fin, extending the whole length of the body. There are no eyes, nor any vestige of any external organ, except a mouth, which is surrounded by small tentacula, like that of the Hag. There is scarcely any trace of a vertebral column, or of ribs; yet the muscles are arranged with great regularity, on the plan of those of Fishes in general. One of the most curious parts of its structure is the complete absence of cerebral hemispheres, and even of ganglia of special sense; the spinal cord being, apparently, the only centre of its nervous system. Thus it may be characterised as one of those " experiments prepared for us by Nature;" exhibiting to us a case, in which the Cerebrum is never developed; the phenomena of which closely correspond with the results that have been obtained

by the artificial removal of that organ. (ANIM. PHYSIOL.

§ 465.)

586. The Geological distribution of this class presents many points of the greatest interest to the Zoologist. As might have been anticipated from what is known of the history of the production of the present crust of the globe, we find remains of Fishes in the very earliest formations which distinctly exhibit the action of water, -that is, which were deposited as sediments in the bed of the ocean; and this long before we have reason to believe that any land animals existed upon the surface of the globe. But the Fishes of this early date were, for the most part, formed upon a very different plan from those of the present epoch, so that there are very few of those now existing, which bear any close resemblance to them; whilst, on the other hand, the greater proportion of