244 PROFESSOR HUXLEY ON THE ANATOMY 
yf the division-masses — i. e., gave rise to them by immediate dry 
The ovum is, in fact, more transparent than in other Rotifera ; and I have observed the 
absence of the germinal vesicle." 
In a subsequent passage Dr. Leydig adverts to these observations as having inclined him 
to alter his previously entertained opinions respecting the fate of the germinal vesicle. 
So far as the Vertebrata are concerned, such evidence as we possess as to the independent 
origin of the embryo-cells appears to be altogether of the weakly negative sort. I do not 
think it can be said that there is adequate foundation for the general assumption that the 
contents of the germinal vesicle take no direct share in their production ; on the contrary, 
as respects the Erog, I find definite evidence tending to a contrary conclusion. Prevost 
and Dumas, and Von Bar, as is well known, proved the existence of a canal leading from 
the centre of the dark part of the Prog's egg to a cavity which Von Bar considered to be 
> 
the seat of the germinal vesicle. Newport (Phil. Trans. 1851) described and figured this 
canal and cavity, and showed that the germinal vesicle is, in the ovarian ovum, lodged in 
the cavity. The vesicle is said to be dense, white, and opake, and its interior to be full of 
secondary cells*. Newport affirms that no trace of the vesicle is to be found in ova that 
have left the ovary, but that an accumulation of white nucleated cells sometimes occupies 
its place, in ova which are in the act of leaving the ovary. 
Remak (Entwickelung der Wirbelthiere, 1855), apparently unacquainted with Newport's 
observations, doubts whether the cavity down to which the canal leads, and which he 
terms Von Bar's ' Kernhohle,' contains the germinal vesicle, though he inclines to the 
opinion that it does. But it is a most important circumstance that he proves (I. c. p. 137) 
that the division of this cavity accompanies each division of the yelk-mass, and that, 
eventually, these cavities become what he terms the nuclei provided with nucleoli, which 
occupy the centres of the division-masses of the yelk, and are the homologues of the 
embryo-cells of Ascaris. If both Newport's and Remak's observations are correct, it 
would seem impossible to deny that the embryo-cells of the Frog proceed from the con- 
tents of the germinal vesicle. 
I think, then, that considering the only case in which the contents of the germinal 
vesicle are not traceable, under circumstances in which it might be reasonably expected 
that, if they really exist, they should be visible, is that observed by Kolliker ; while, on 
the other hand, the equally definite observations of Nelson, Muller, Gegenbaur, and 
myself (and the less distinct evidence of Newport, Remak, and of Leydig) testify to 
the origin of the blastoderm in one way or the other from the contents of the germinal 
vesicle, in various members of no less than fourf out of the five primary divisions of the 
animal kingdom ; the balance of the evidence is in favour of the conclusion that the em- 
bryo-cells are the progeny of another cell, and that here, as elsewhere, extracellular cell- 
development is a phenomenon of rare, if not of altogether questionable, occurrence. 
* Newport, it should be observed, used the term ' cell * not very critically. But, ten years ago, cell-worship had 
attained its culminating point. 
f Ccelenterata, Mollusca, Annulosa, Vertebrata. I may add, that the first appearance of the blastoderm on the 
surface of the ovisac of Pyrosoma is so like that of the blastoderm in the ovum of any of the higher Articulata, as 
strongly to suggest a similarity of origin. 
