On a platypus embryo from the intra-uterine egg

A PLATYPUS EMBRYO, laid as 1 5 mm.by 1 2 mm.Three other females were shot on the same date, and these had obviously just laid their eggs, as evidenced l^y the emptiness and large size of the left uterus andhj the jDresence and condition of corpora lutea in the ovary.Moreover, the mammary glands in all four females were of approximately the same size.The tubules were arranged in a fan-like fashion, radiating outwards from the, at this stage, very small bare area of the ventral abdominal wall, and measured 5 cm.in length.From the size of these eggs as compared with Caldwell's, and from the condition of the other three females shot on the same date, we may reasonably conclude that they were just ready to be laid.The only other recorded measurements besides Caldwell's of the size of the Platypus eggs when laid are contained in a paper by Geoffroy KSt.Hilaire published in 1829.^'The eggs, nine in number, were found lying on a rough nest in a small burrow on the banks of the River Hawkesbury, N.S.W., and measured 1| inches (34 mm.) long by f of an inch (19 mm.) broad.The eggs here described were probably not those of Platypus at all : as St. Hilaire himself afterwards pointed out, they could not on account of their size pass through the pelvis, and he then came to the conclusion that in Platypus the eggs must be hatched inside !The eggs were opened immediately after the animal was shot and their contents joreserved in picro-sulphuric acid.The embryos were stained with borax-carmine, imbedded in paraffin and cut into serial sections with the Cambridge microtome.To our friend.Prof. J. T. Wilson, we are indebted not only for many valuable suggestions but for much