218 SUPPLEMENT.
or the cell-membrane of the yelk-cell, closely encompasses the germ-vesicle at first and then gradually expands, while between it and the vesicle a transparent fluid collects; in which, at a later period, a turbidness commences, occurring first in the neighbourhood of the germ-vesicle. Wagner had thus dis- covered in the course of his observations that the details of the process were just what must have been expected according to the theory of the unity of the principle of development for all elementary particles of the organism. That the germ- vesicle is the nucleus of the yelk-cell appears to me therefore to be scarcely dubitable. The illustration given by Wagner also shows that the germinal spot is first developed, then the germ-vesicle around it, and around this again the yelk-cell. It is not surprising that granulous contents may form within the germ-vesicle at a subsequent period, since the same thing occurs in the indubitable nucleus of the adipose cells of the fish, and the formation of the cell is probably nothing more than a repetition of that same process around the nucleus, by means of which the nucleus was originally formed around the nucleolus.
