588 SYDNEY J. HICKSON. 
and well-defined chromatin meshwork. The cell-substance 
surrounding each of these nuclei is distinguished from the en- 
dodermal cell-substance in being considerably more transparent 
and homogeneous, and in taking up the staining reagents less 
readily. 
I failed entirely to find even a trace of a limiting membrane 
between the cell-substance surrounding them and the general 
endoderm. When I came to examine these bodies with greater 
care, and to compare their structure with that of the youngest 
ova I had previously found, no doubt remained that they were 
very young ova. I could find no trace of any such structures 
in the ectoderm, and no satisfactory evidence that they undergo 
any process of migration in the endoderm of the canals. In 
some cases, it is true, they exhibit amceboid processes (PI. 
XXXVIII, fig. 5); but these cannot be taken as an infallible 
sign of movement, as it is quite possible they are merely used 
for the purpose of feeding more readily upon the fluids of the 
endodermal tissue. 
The nucleus or germinal vesicle of the young ovum under- 
goes no noticeable change except a slight increase in size until 
the ovum approaches maturity. The first change to be noted 
is that it shifts its position from the centre towards the distal 
pole, and at the same time becoming more or less oval in 
shape, its longest diameter being approximately at right angles 
to a line drawn from the proximal to the distal pole of the 
ovum, it loses its regularity of outline. 
On the distal side a small papillate process makes its 
appearance (Pl. XXXVIII, fig. 8) which contains a concen- 
tration of the chromatin network. ‘This process represents 
the portion of the germinal vesicle that is subsequently dis- 
charged with the first polar vesicle. The germinal spot, even 
in the younger ova a very prominent structure, attains at this 
stage its largest size. It always stains deeply in borax- 
carmine. When examined by a high power a regular tesse- 
lated appearance can be made out, which seems to be due 
to the presence of an intra-nucleolar chromatin meshwork 
(fig. 9). 
