On the mode of breeding of the ovo-viviparous shark, and on the aëration of the fætal blood in different classes of animals

Abstract

With a view to understanding more fully the structure of the Squalus maximus, of which Mr. Home has lately published an account, he has examined with attention that of the Squalus acanthius, which appears to resemble it closely in its internal structure, and has the advantage of being very easily obtained upon the Sussex coast, where it is very common. After describing minutely the external organs of generation in both male and female, the author traces the progress of the ovaria from the time that the yolks are no larger than peas, till they become as large as walnuts, when they pass into the oviduct. The number of yolks differs in different fish; and even in the same fish Mr. H. has seen five yolks in one ovarium and only two in the other. The oviducts then enlarge, and become exceedingly extended, and divided by contraction of its coats into three cavities, the last of which is ten inches in length, and is that in which the eggs are retained till the young fishes are formed, and capable of taking care of themselves. The eggs, however, are not loose as in the oviducts of birds, but are grouped together to the number of three, four, or five, in membranous bags, containing a transparent jelly, in which the young fish swims about after it is formed, with the yolk attached to its belly by a long chord, consisting of blood-vessels. If the bag be torn and the fish taken out and put into water with its yolk attached to it, it swims about; but if the vessels of the chord are wounded, it dies immediately.