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, in which the vitelline-membrane closely en- 

 compasses the germ-vesicle, it is impossible to decide whether 

 it lie 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, 1 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 points 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 



1 < 



See Note, p. :>.'{. 



