THE DEVELOPMENT OF PERIPATUS CAPENSIS. 
455 
The passage of the ova down the oviducts and uteri is 
effected by the peristaltic contraction of the walls of these 
structures. I have never been able to see cilia in the genera- 
tive organs, or in any other part of the body of Peripatus 
capensis. 1 
The living ripe ovarian ovum is somewhat elliptical in shape 
and of dark colour by transmitted light. The opacity is due 
to the presence of granules, which are uniformly distributed 
in the protoplasm, but absent altogether from the larger 
germinal vesicle. 
As I have stated above, I propose to defer my account of the 
ovary and ovarian ovum until their development is con- 
sidered. 
The Fertilised Ovum. 
The youngest ovum found in the oviduct is shown on 
PI. XXXI, fig. 1. It is of an elongated form — length ’4 mm. 
— and is surrounded by a transparent, structureless mem- 
brane, which is either a vitelline membrane or derived from 
the follicular cells surrounding the young ovarian ovum. 
This membrane persists until birth ; it has a dense structure 
and allows fluid to pass through it by diffusion. Water 
diffuses through it more rapidly than alcohol, and alcohol 
more rapidly than turpentine ; so that when an embryo is 
removed suddenly from weak alcohol into strong, or from 
absolute alcohol into turpentine, the membrane shrinks and 
closely invests the embryo ; in fact, in the latter case all the 
alcohol diffuses out before any turpentine enters, so that the 
membrane completely collapses and squashes the embryo flat. 
When, on the other hand, an embryo is removed from strong 
alcohol into weak, or into water, the water passes in more 
rapidly than the alcohol passes out, so that the membrane is 
distended, and the space between it and the embryo much 
enlarged. In the normal embryos there always is a space 
between the membrane and the ovum, which contains fluid in 
1 This remark applies to the nephridia, all parts of which I have carefully 
examined in the fresh state without ever seeing a trace of cilia. 
VOL. XXV. MEW SER. 
G G 
