378 AliTHUR DKNDY. 



polygonal corpuscle of almost homogeneous structure. The 

 polygonal shape of the corpuscles is apparently due to mutual 

 pressure. Their diameter is about 0"0]6 mm. Both the 

 globular body and the enclosing corpuscle appear to be 

 stained fairly darkly by alcoholic solution of eosin, but osmic 

 acid (2 per cent, solution) has little effect on either^ and in 

 sections treated by the borax-carmine and acid-alcohol 

 method they appear quite unstained. Whether the highly 

 refractive yolk granules observed in the ovarian eggs and 

 shown in fig. 15 have any relation to the corpuscles and their 

 contained globules, it is impossible at present to say with any 

 degree of certainty, but it seems not unlikely that the yolk 

 is first deposited in the finely granular form, and subsequently 

 converted into the comparatively large globules with their 

 enveloping corpuscles. The appearances shown in fig. 16 

 support this hypothesis. 



The Egg Envelopes. — The ovarian egg, as we have 

 already seen^ is enclosed in a distinct, transparent, appa- 

 rently structureless vitelline membrane, which attains only a 

 moderate thickness, and persists inside the chorion or egg- 

 shell for a very long time, probably throughout the entire 

 development, for I found it around an embryo in an egg 

 which had been laid for at least eight and a half months. 

 This vitelline membrane is, I believe, homologous with the 

 thin membrane which alone surrounds the embryo of Peri- 

 patus Leuckartii (New South Wales), and which Steel (1) 

 has shown to persist until birth. Willey (1) considers this 

 membrane in the New South Wales species to be a chorion 

 and not a vitelline membrane, but I can see no reason for 

 maintaining this view. The " shell " described by Miss 

 Sheldon (2) in the ovarian eggs of P. novse-zealaudi^, 

 P. Balfouri and P. capensis, is also probably a vitelline 

 membrane, but the shell which the same writer [Sheldon (1)] 

 describes as lying outside the vitelline membrane in the 

 uterine egg of P. nov£e-zealandi£e is no doubt correctly 

 regarded as a chorion. 



In Ooperipatus oviparus and 0. viridimaculatus 



