SHARK. 



649 



and that life is far more secure than the life in the 

 egg of a bird or an oviparous reptile, to which it 

 bears, in some respects, a considerable resemblance. 

 The shell or covering of the egg, in these fishes, is of 

 a horny consistence, tough, strong, and not liable either 

 to be broken or torn ; and it is generally furnished 

 with claspers or tendrils, which twine round the stems 

 of sea -weed, and other fixed substances, where the 

 eggs remain at a sort of anchor, until they are 

 hatched. These eggs are, we believe, chiefly brought 

 forward in pairs, the ovoviviparous ones being 

 hatched, one in each oviduct ; and the oviparous 

 ones receiving their horny covering there, in the same 

 manner as the eggs receive their carbonaceous shell. 

 The egg is usually of an oblong form, with the ten- 

 drils, one at each of the four corners ; and those 

 which are at the end to which the tail of the fish inside 

 is to be directed, after it is formed, are stronger, and 

 have more of a prehensile structure than those at the 

 end where the head is to be situated. Near the head of 

 the embryo fish there is a small longitudinal opening 

 in the horny covering of the egg for admitting water ; 

 and at the opposite end there is a similar one for al- 

 lowing the water to escape. Thus, the fish inside 

 the close and firm case, has a supply of water as soon 

 as it is capable of profiting by it. Near the head, 

 too, there is a part where the horny shell is more 

 easily disrupted than in any other ; and when the 

 proper time arrives, this gives way, and the fish comes 

 forth a free tenant of the waters. But the transi- 

 tion from the one state to the other is not instanta- 

 neous, but gradual ; for when the young fish comes 

 out of the egg, it carries with it, in a capsule con- 

 nected by a kind of umbilical peduncle, a portion of 

 the same vitellus which had supported it within the 

 covering. The general economy of the young shark 

 (or ray) is, therefore, the same in principle as that of 

 the spawning fishes ; the case, or " purse," as it is 

 called, when found empty on the beach, or floating, 

 being the addition. Young salmon, for instance, re- 

 main " on the egg," and are supported by the vitellus, 

 just in the same manner as young sharks are, only 

 they are in vast numbers, in the sand or gravel, where 

 they have been deposited by the parent fishes, and 

 there is no protecting case to the young fish ; whereas 

 the young shark is not alone upon the waters, but 

 provided with a case which affords it protection 

 against the water, and also no doubt against enemies ; 

 for it is not likely that many fishes will feed on the eggs 

 of sharks and rays, considering the strength of their 

 covering ; whereas many fishes, birds, and other ani- 

 mals, eat the eggs of the spawning fishes. 



There is one other point connected with the eco- 

 nomy of the young shark in its case, which is worthy 

 of notice, as showing how perfectly the adaptations of 

 nature are, even in what appear to us to be the most 

 minute particulars. The young of the spawning fish 

 is in the free water, and it has the free use of its 

 mouth and its gill-covers, so that it can breathe in the 

 same way that the full-grown lish breathes, from the 

 commencement. It is different with the young shark, 

 pent up as it is in its case, with the body bent, and 

 the head confined. The water, too, gets access to 

 it only by one small opening in the case, and it 

 escapes by another. Hence, it is impossible that the 

 young shark in the case can breathe in the same 

 manner as a fully developed one does after it is in the 

 sea. The case can clearlv give it no assistance in 

 breathing, as the case has iao vitality. But the ani- 



mal thus confined is placed in. circumstances so dif- 

 ferent from those in which it is afterwards to act as 

 the most independent and discursive inhabitant of 

 the water, that it requires some assistance. The 

 difference between the two states of the shark or the 

 ray is not so great certainly as that between the state 

 of a tadpole or a larva living in the water, and the 

 batrachian reptile or the perfect insect living in the 

 air ; for the medium of breathing is different in them, 

 and only the mode is different here. Therefore the 

 desideratum is not a different kind of breathing ap- 

 paratus for the two states, but a modification of the 

 same apparatus. This is found to be provided in all 

 the young of the sharks and rays that have been ex- 

 amined in the case. This consists of a filament of 

 the substance of the gill, projecting from the gill 

 opening, and containing a vessel (or vessels ?) in 

 which the blood is exposed to the action of the water ; 

 and thus the same purpose is answered without the 

 action of the internal gills. When the shark or the 

 ray comes into the free water, those fibrous appen- 

 dages would be as inconvenient as they are necessary 

 when it is in the case ; and they are accordingly 

 very speedily absorbed. 



One can hardly fail in being struck with the re- 

 semblance which there is in these supernumerary 

 gills in the selacian fish, while in the case, to the gills 

 which those reptiles and insects which spend the first 

 stage of their animated existence in the water have 

 while they remain there. In them the gills are no 

 part of what is to be the permanent structure of the 

 animal, they are mere external appendages developed 

 for a temporary purpose ; while they answer that 

 purpose, the proper organs which are to be promi- 

 nent are either undeveloped or dormant ; but they 

 are formed or become active as soon as they are 

 wanted. Just so in these fishes, the internal gills 

 remain in a great measure inert, until the animal 

 comes into the free water, and requires their use. 



This provision in the young shark or ray appears, 

 after it has been explained, to be so rery much in 

 accordance with the general action of nature, that 

 one looks upon it as a thing indispensable, and there- 

 fore of course. But this is only after the explanation 

 has been given ; for before then, some naturalists of 

 no mean name or industry considered these appen- 

 dages as characteristic of a species of shark, which 

 had been met with only in the small specimen which 

 had them, and to which they gave the name of 

 Squalus ciliaris, 



This shows how necessary it is for every one 

 who puts his hand to the subject of natural history, 

 more especially in the folding of new species or varie- 

 ties to which tyros in the matter are exceedingly 

 prone, to inform himself well upon all points of 

 physiology, both immediate and collateral ; for it is 

 highly probable that very many of the obscure spe- 

 cies in general, which rest upon no surer foundation 

 than a single museum specimen, would be found en- 

 titled to no such distinction, if their physiology and 

 place and relation in nature were rightly understood. 



The Selacii, but especially the sharks as the typical 

 subfamily, being thus formed by nature for the most 

 powerful exertions, and being exempted from some 

 of the severest duties that devolve upon other fishes, 

 may fairly, on the principle of the general analogy, 

 and even without a distinct knowledge of their habits, 

 be presumed to have a very energetic and important 

 part to play in nature. 



