Studies in Australian sharks. No. 2
Abstract
It was known to Aristotle, some 350 years B.C., that of two common "Hounds" of the Mediterranean, the embryos of one were developed by the medium of a placenta produced in the uterus, and that the embryos of the other were developed without such placenta. The condition in the former species, Mustelus laevis, is thus described by Balfour :- "The vascular surface of the yolk-sack becomes raised into a number of folds, which fit into corresponding depressions in the vascular walls of the uterus. The yolk-sack becomes in this way firmly attached to the walls of the uterus, and the two together constitute a kind of placenta"
