WEISMANN'S THEORY OF THE GERMPLASM 95 



the lirst transverse and horizontal cleavage-planes 

 divide the protoplasm of the egg into pieces pre- 

 determined for the formation of the anterior and 

 posterior, dorsal and ventral, parts of the embryo. 



But I think I have shown beyond possibility of 

 doubt that these events are due not to the exist- 

 ence of special, mysteriously working groups of 

 determinants within the nucleus, but merely to the 

 specific shape of the whole egg and to the segregation 

 of the yolk. It is self-evident that, as the body of the 

 embryo builds itself up from the actual material of 

 the egg, the way in which the material of the egg 

 is disposed must be of great influence upon the 

 formation of the shape of the embryo. And so, in 

 a recently published work, I stated that the grow- 

 ing embryo, especially in its early stages, must 

 conform in many ways to the shape of the fer- 

 tilised egg. 



Thus, to bear out what I have been saying by 

 actual examples, the distribution of the actual 

 particles of the fertilised egg must correspond to 

 the disposition of the bulk of material in the 

 blastosphere ; for, in the breaking up into cells, 

 the spacial arrangement of the substances of 

 different weights undergoes no change. Thus, 

 amphibia, the eggs of which have the poles 

 different in character, produce blastospheres the 

 poles of which are unlike ; while eggs, like those 

 of the fowl, where the yolk does not divide, give 

 rise to blastospheres with unsegmented yolk. In 

 such cases the more or less complete segregation ot 

 the yolk and gravity, which causes a separation ot 



