POLAR BODIES. 21 



IIIj fig. 1). I have never seen an ordinary vesicular nucleus 

 in a polar body. 



The male pronucleus varied in the different ova. It was 

 always placed near the surface almost opposite the female 

 nucleus. 



2. The ovum in which the male and female pronuclei had 

 united^ all presented essentially the same features so far as the 

 body of the ovum was concerned, but differed in the structure 

 of their nuclei. The structure of the ovum will readily be 

 understood after an examination of fig. 8, PI. III. There 

 is a well-marked cavity traversed by irregular strands of proto- 

 plasm. The network is much closer round the nucleus than 

 elsewhere. This feature of the perinuclear protoplasm is much 

 more marked than in the earlier ova, and causes the large 

 opacity noticeable in surface views of the ova of this stage 

 (PI. 1, fig. 1). 



The polar bodies present no essential differences from those 

 of the previous stage. They persist during the early stages of 

 segmentation. 



The nucleus presented different appearances in the different 

 specimens. In all, however, it was distinguished by its large 

 sizes, and it seems to be the cause of the central transparency 

 of the dark patch seen in fresh ova. Its structure will be 

 described below. 



The Segmentation. 



The general features of the segmentation have already been 

 described in the first chapter. 



The first furrow passes through the centre of the opaque 

 patch, and at right angles to the long axis of the ovum. Each 

 of the two segments resulting from this consists of a small 



* I have not observed the conjugation of these nuclei. I assume its occur- 

 rence from the analogy of other animals. In any case the ova I am about 

 to describe were undoubtedly older than the preceding, and the nucleus is the 

 first segmentation nucleus. 



