358 ON THE ANATOMY AND DEVELOPMENT OF PYROSOMA 
and the round, sharply-defined germinal spot strikes the eye at once. 
If I now move the slide a little way, I. bring into view a large ovisac 
about j4nd of an inch in diameter. In this, it is only with difficulty 
that I can trace the outline of the germinal vesicle, and nothing is to 
be seen of the germinal spot. This indistinctness of the germinal 
vesicle does not arise from want of size or clear definition ; for, if I 
put on a high power, I find it to have a diameter of ,4,th of an inch, 
and its contour is perfectly well marked. The yellow deposit occupies 
about half its cavity as before, but it is paler; and partly on this 
account, and partly by reason of a further change in the structure of 
the epithelium of the ovisac, the vesicle is less obvious than previ- 
ously. Ofthe germinal spot not a trace is to be seen anywhere, 
although the vesicle and its contents are quite transparent. Whether 
the contents exhibit any new structure or not cannot certainly be 
made out, on account of the interference of the wall of the ovisac, 
through which the germinal vesicle is seen. In another ovisac in this 
stage, also about ~;nd of an inch in diameter, the germinal vesicle, 
very similar to that first described, measures z3yth of an inch in 
length, and is half filled with the yellow deposit. No vestige of the 
germinal spot is to be seen, but, on that side of the contents which in 
earlier stages is occupied by the germinal spot, there are a number 
of minute, spheroidal clear granules, none exceeding zgdgath of an 
inch in diameter and arranged so as to form an elongated patch on 
the surface of the contents, the rest of which is quite free from such 
bodies. In another ovisac of about the same size the germinal 
vesicle is »1,th of an inch in diameter with pretty nearly half that 
thickness, and similar granules are observable upon the face of its 
contents, while there is nothing to be seen of a germinal spot. 
But the best example of this stage is that afforded by yet another 
ovisac th of an inch in diameter, whose germinal vesicle, 35th of 
an inch in diameter, is represented in fig. 86. Here the contents can 
be searched through and through with the greatest ease ; but not the 
least trace of a germinal spot is discoverable, while the minute clear 
corpuscles zpdgath to ygsoth of an inch in diameter, scattered over 
the face of the contents, are exceedingly distinct. Whether they are 
free, or whether they are imbedded in any clear substance, I cannot 
say certainly, but I suspect the latter to be the case. 
Putting the facts observed in this stage together, we find, that in 
ovisacs between th and ;4th of an inch in diameter, the germinal 
vesicle increases in size until it attains as much as s},th of an inch in 
long diameter ; and that the germinal spot, as such, entirely disap- 
pears. On the other hand, on that side of the contents towards the 
