1 70 A/C/^VSOA: [Vol. XV. 



As the cytoplasm increases at the vegetative pole, the 

 nuclear pole becomes more and more crowded, till it, with 

 the germinal vesicle, spreads out over the surface of the vege- 

 tative pole as previously described (PI. XVI, Fig. 104; PL 

 XIII, Figs. II, 14). 



It is to be remembered that no true yolk spheres exist yet, 

 for these appear only after the discharge of the egg into the 

 ovarian tube (PI. XIII, Figs. 12, 17). 



This process, it seems to me, has some of the features of 

 gastrulation by invagination. The animal portion, less laden 

 with food material, finally comes to lie externally to the vege- 

 tative portion. The gastrulation, therefore, might be said to 

 take place previous to fertilization, or even to yolk forma- 

 tion, and the cleavage by delamination, described by Kingsley 

 and also suggested by Brooks ('85) and Bruce ('85), might 

 be regarded as only a continuation of these early conditions. 

 The appearance after the discharge of the egg of a large accu- 

 mulation of yolk spheres obscures these relations. Yet it is 

 difficult to escape the conviction that a relation of some sort 

 exists between these later developmental processes and the 

 conditions that are found to exist even at the beginning 

 of the period of growth of the egg (PI. XIV, Figs. 42-47). 

 According to both Kingsley and Brooks, the development of 

 the fertilized egg of Limulus is peculiar in that the first 

 evidence of cleavage appears only on the surface. From 

 what I am able to gather from the accounts of these writers, 

 this division into cells is a secondary matter, the whole egg 

 ultimately being converted into an embryo. 



The polarity of the ovarian egg of Limulus is not a matter 

 of chance. It is not acquired during the growth of the egg, 

 but it dates from the beginning. (See PIl. XIV-XVI.) The 

 germinal vesicle alone does not constitute this polarity ; for, as 

 has been shown, the centrosome with its cytoplasm exists from 

 the very beginning. 



In the history of the germinal vesicle, more particularly the 

 chromatin, I find nothing on which to base the assumption 

 that it is the ovigenic element, and that it is this which pre- 

 sides over all the formative processes. I find no evidence that 



