GERMINAL MEMBRANE. 47 
separate them. Although the position of the vesicle in the 
middle of the yelk-cell affords evidence rather in favour of its 
being regarded as a young cell, yet it is not altogether incon- 
sistent with its character as a nucleus; for it is only during 
the earliest formation of the cell that the nucleus is required 
to be connected with it; it is frequently disconnected at a 
later period, and lies loose in the cell. At that stage of deve- 
lopment, however, im which the vitelline-membrane closely en- 
compasses the germ-vesicle, it is impossible to decide whether 
it he in the middle or on the wall of the cell. This point, 
therefore, is of more ideal than practical importance for the 
prosecution of the investigation. 
The third point relates to the signification which attaches 
to the individual parts of the germ-vesicle. It may be hol- 
low consistently with both views. Although we are not as yet 
acquainted with any hollow nuclei in plants,’ we have never- 
theless found nuclei in cartilages which were hollow, and de- 
cidedly to be regarded as cytoblasts. The question now arises, 
what are Wagner’s spots or spot? If the germ-vesicle be con- 
sidered to be a young cell, one of them may be its nucleus, and 
the rest cell-contents, or nuclei of young cells, which will be 
developed afterwards ; if it be regarded as nucleus, the spots 
may either be nucleoli, or merely its contents. It is a fact in 
favour of the former view, that only one spot is present in 
most instances, the others being usually produced at a later 
period. Wagner has sometimes observed one or more minute 
points in this single spot, and has delineated them from Alcedo 
hispida, Lepus cuniculus, Ovis aries, &c.; I have also sometimes 
met with small points of this kind which gave the spot, in some 
degree, the appearance of a nucleus adhering to the wall of the 
cell, and containing within it these little pomts as its nucleoli. 
Meanwhile, their presence is too inconstant, and they are gene- 
rally too indefinite, to permit of our attributing any importance 
to them in the decision of the present question. The extra- 
ordinary number in which they frequently occur is opposed to 
their being regarded as nucleoli within the germ-vesicle, pre- 
suming it to be a cell-nucleus, for in fishes they sometimes fill 
the entire vesicle, at least, being closely crowded, they cover 
' See Note, p. 33. 
