OVUM IN THE OAPE AND NEW ZEALAND PERIPATUS. 283 



which radiate from the pronucleus towards the centre of the 



egg. 



In all the other ova of P. capensis in which the formation 

 of polar bodies was taking place, I was unable to see any pro- 

 nucleus, although I believe that that structure must be present 

 in them, since it seems certain that fertilization must take 

 place in the ovary. In several cases there were special aggre- 

 gations of protoplasm, in one of which the male pronucleus 

 may have been present, although I was not able to distinguish 

 it, and I am inclined to think that for a short time after 

 entering the ovum it is invisible, possibly from a lack of 

 chromatin. 



In the next stage, when the polar bodies are both formed, 

 the male and female pronuclei are both present as very well- 

 marked structures. Two sections through an egg of this stage 

 are shown in figs. 14 a and 14 b. Fig. 14 a passes through the 

 second polar body and the female pronucleus ; the former lies 

 in a depression on the surface of the ovum and is not com- 

 pletely separated from it, being connected with its proto- 

 plasmic reticulum; it contains three chromatin granules. 

 Just below it lies the female pronucleus, which is now in the 

 resting condition, and has begun to assume the lobed structure, 

 which was described by Mr. Sedgwick (14) as being so charac- 

 teristic of the segmentation nuclei, and is divided by a septum 

 into two compartments, in each of which are a few chro- 

 matin granules. It is not surrounded by any special dense 

 protoplasm, but its wall is continuous with the general loose 

 reticulum of the egg. Fig. 14 b, which is several sections 

 removed from fig. 14 a, passes through the male pronucleus, 

 which is now a very prominent feature in the egg. It is 

 round in shape, and lies near the centre of the egg, being con- 

 nected with the periphery at the side removed from the female 

 pronucleus by a denser mass of protoplasm, which in transverse 

 section is roughly wedge-shaped. In these two figures only 

 the protoplasm in the neighbourhood of the pronuclei is figured. 

 Seen under a high power, the male pronucleus is seen not 

 to be sharply marked off from the extra-nuclear substance. 



