Page:Natural History, Fishes.djvu/317

Rh weaker and more easily ruptured than any other part; a provision for the easy exclusion of the animal, which takes place before the entire absorption of the vitellus or yolk of the egg, the remainder being attached to the body of the young fish, enclosed in a capsule, which for a while it carries about. The position of the animal, while within the egg, is with the head doubled back towards the tail, one very unfavourable for the process of breathing by internal gills, and hence there is an interesting provision made to meet the emergency. On each side a filament of the substance of the gills projects from the gill-opening, containing vessels in which the blood is exposed to the action of the water. These processes are gradually absorbed after the fish is excluded, until which the internal gills are scarcely capable of respiration. How curious an analogy we here discover with the Frogs and Newts among the Reptiles; and how impressively do we learn the Divine benevolence, when we find that the object of so much contrivance and care is the dreaded and hated Shark!

In some species the horny capsules in which the young are enclosed at birth are destitute of the filamentous prolongations of the angles; in some they have but two projecting points, one end being rounded; while other species, as the Penny Dog (Galeus vulgaris), and Smooth Hound, (Mustelus lævis), of our own shores, bring forth their young alive and fully formed, without any capsule or covering at all.

A hundred and fourteen species are reckoned by Prince Bonaparte to belong to this Family;