380 ON THE ANATOMY AND DEVELOPMENT OF PYROSOMA 
division of the yelk; and the products of the division of the germinal 
vesicle behave similarly, in relation to the subdivision of the yelk- 
masses. I observed this process of yelk-division in Agalmopsis, 
Physophora, Forskalia, Hippopodius, and Diphyes, without noticing 
any important differences among them.” 
Leydig expresses the same conclusion, though more guardedly, in 
his account of the development of the ova of Notommata Sieboldii! :— 
“The nuclei of the division-masses are very clear ; and it appeared 
to me as tf the homogeneous, clear nucleus of the ripe ovum (the ger- 
minal vesicle) stood in a genetic relation to the nuclet of the division- 
masses—t. ¢., gave rise to them by immediate division. The ovum 
is, in fact, more transparent than in other Rotzfera; 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 Frog, 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 Frog’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 opaque, 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 unac- 
quainted 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 
1 ««Ueber den Bau und die systematische Stellung der Raderthiere.” Siebold und 
Kolliker’s Zeitschrift, 1855. 
2 Newport, it should be observed, used the term ‘cell’ not very critically. But ten 
years ago, cell-worship had attained its culminating point. 
