178 ADAM SEDGWIOK. 
In all, except one which I have figured (Pl. XII, fig. 1), it 
appeared to be undergoing changes in connection with the 
formation of the two polar bodies. I have four ova of this 
stage, and they all presented structures which I take to be the 
male pronucleus. 
The polar bodies are two in number ; when fully formed they 
have a diameter of about ‘016 mm. Each of them contains 
a small number of deeply-staining bodies which are placed 
close together in the centre and represent the nucleus (PI. 
XII, fig. 1). Ihave 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, Pl. XII. 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 
(Parc le Pls eX fie, 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. 
1 T 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. 
