Egg of the Shark.

Fig. 326. Egg of the Shark.

(1852). The means employed for this end are simple and beautiful. About the middle of the oviduct of the female there is a thick glandular mass, destined to secrete a horny shell, in which the yelk and white of the egg become encased. The egg when complete has somewhat the shape of a pillow-case, with the four corners lengthened out into long tendril-like cords (fig. 326), whereby the egg is entangled amongst the sea-weed at the bottom of the ocean. A brittle egg-shell would soon be destroyed by the beating of the waves; hence the necessity for the corneous nature of the envelope; and yet, how is the feeble embryo to escape from such a tough and leather-like cradle? This likewise has been provided for: the egg remains permanently open at one extremity, or, to carry out our humble simile, one end of the pillow-case is left unsewn; the slightest pressure from within, therefore, separates the valvular lips of the opening; and no sooner has the little Shark thus extricated itself from its confinement than the two sides close again so accurately that the fissure is not at all perceptible *.

Viscera of the Shark, in situ: a, the heart; b, gill openings.

Fig. 327. Viscera of the Shark, in situ: a, the heart; b, gill-openings; c c c, lobes of the liver; d, e,f, h, alimentary canal; i, appendage to the intestine; g, biliary duct; n, the testis; o, p, vas deferens; k, intromittent organ; r,s, openings communicating with the peritoneal cavity; I, claspers.

(1853). The sexual organs of the male Chondropterygii are very remarkable, and their real character is not properly understood. The testicle (fig. 327, n) is large, and occupies the same position as the ovary of the female; but the singularity of this testis consists in its being made up of two portions, one of which has an excretory duct, while the other, although equally bulky, has none.

(1854). The former portion, when minutely examined, is composed of an immense assemblage of flexuous secerning vessels, that pour their secretion into a long and tortuous vas deferens (o), which, after running in a zigzag course nearly the whole length of the abdomen, dilates into a capacious reservoir of semen (p), and ultimately terminates with its fellow of the opposite side in a conical fleshy organ (k), which may be presumed to answer the purpose of an intromittent apparatus.

(1855). The second portion of the testis appears to consist of globular bodies having no excretory duct whatever; and it is not impossible that this is an organ analogous to the testis of the Lamprey, and that its secretion escapes into the abdominal cavity, to be expelled through two orifices (s s) situated on each side of the anus, whereby a free communication exists between the interior of the peritoneal sac and the external surface of the body.

(1856). In these highly-organized genera impregnation takes place internally, and the male is furnished with two strong prehensile organs called clasjpers (Z), by means of which he seizes and securely holds the female during copulation.

* According to Cuvier, in those Sharks which are viviparous (that is, whose young are hatched in the oviduct prior to their expulsion) this egg-shell is never formed, and the investments of the foetus remain permanently membranous (loc. cit. p. 397).