604. ARTHUR THOMSON. 
granular cells there is thus no radical difference; they are 
formed in the same region of the ovum, and in the same way, 
but at different epochs in ovogenesis, and with unequal cellular 
differentiation. Sabatier asserted, further, that in the ova of 
fish, amphibia, cat, dog, cow, and homo, bodies are eliminated 
from the germinal vesicle, which are destined to become the 
cells of the Graaffian follicle, but which are, as in Tunicata, 
formed without the participation of the germinal vesicle. Fol 
has also observed in frog, triton, rabbit, cat, and once in homo, 
phenomena which he could only explain on the supposition of 
migration of nuclear elements from the germinal vesicle, 
though, in the absence of decisive proof, he adds, ‘1 can hardly 
believe that these cells, endogenously formed within the ova, 
could form all the epithelial envelope of the Graafian follicle. 
Sarasin (‘ Biol. Centblt.,’ i, 4) has also described Schifer’s 
pseude-nuclei in the Reptilian ovum. 
In Phallusia Roule described the origin of adventitious 
nucleoli within the germinal vesicle. These migrate into the 
vitellus, become surrounded by a clear zone of protoplasm, 
travel to the periphery, and form first the follicular, and, at a 
later stage, the “test” cells. The follicular envelope mcreases 
by the division of the cells which have migrated outwards. 
The formation of nucleoli described by Roule and the budding 
described by Fol are emphatically contradicted by Sabatier. 
In the oogenesis of Appendicularia Bolles Lee described 
nuclear budding of the primitive nuclei of the ovarian portion 
of the ovotestis, and the liberation of the buds to become on 
the one hand definite ova, and on the other the epithelial 
cells enveloping these. Balbiani next described in Geophilus 
phenomena which corroborated Fol and Roule rather than 
Sabatier. The nuclear filament of the germinal vesicle breaks 
up into rounded-off portions, which find their way outwards ; 
in some cases a sort of stolon was prolonged out from the 
nucleus, in others the budding took place all round. The de- 
‘tached buds travel outwards to the periphery, and the follicular 
epithelium is thus gradually formed. The final germinal 
vesicle is simply a follicular cell, which does not travel out- 
