504 BULLETIN OF THE 



first feebly expressed, this ring soon becomes well defined and has on 

 either margin a border of yolk substance that is destitute of yolk spheres, 

 but densely packed with fine granules, and appears whitish in reflected 

 light. This ring deepens and at the same time approaches the pole so 

 that a central cup-shaped mass of the yolk is nearly cut off from the 

 main mass, having only a slender stalk of connection, like the stem of a 

 goblet. At the same time the outer or equatorial margin of the ring 

 becomes denticulate, and its substance stretches out towards the equator 

 of the egg in the form of rays, — the ^^ring rays^ About ten minutes 

 after the appearance of the first ring a second one appears at the aboral 

 (vegetative) pole of the egg^ but in narrowing upon the enclosed space it 

 does not dip so deeply into the yolk, and ultimately forms a superficial 

 disk with thickened margins. This also sends out "ring rays." At the 

 approach of cleavage the ring at the oral pole is made to assume the 

 shape of a crescent by the movement of the cup-shaped mass of yolk 

 toward that side of the ring which is nearest the plane of the coming 

 cleavage. Both sets of ring rays become more and more feeble at the 

 approach of segmentation. 



On sections it is seen that the whitish substance which appears on 

 the borders of the rings forms a continuous layer underlying them. 

 After they have assumed, the oral one the shape of a compact, well- 

 defined ring with nearly circular section, — the aboral one the shape of an 

 oblate spheroid, — the " whitish" substance underlying and more or less 

 surrounding them is seen to plunge deeply into the yolk at about the 

 time the first cleavage amphiaster is forming. The substance of the 

 rings takes the same course toward the cleavage nucleus. In osmic acid 

 and carmine preparations the ring substance behaves in the same manner 

 as the substance of the "nucleus"; it is therefore "probably nuclear 

 matter, or something very analogous." The rings " possibly contribute 

 some elements to the nucleus, which may either induce or stimulate the 

 molecular changes, which result in the formation of the primary cleavage 

 amphiaster. ^^ 



The interpretation which Whitman gives the small sharply defined 

 bodies occupying the centre of what he regards as the pronuclei is, as 

 he himself fully understood, radically at variance with the more gener- 

 ally accepted view. Most observers have considered the structures in 

 question, even though two or perhaps several in number, as the pro- 

 nuclei themselves, and the surrounding ill-defined plasmic substance as 

 a specially differentiated, or at least segregated, portion of the yolk 

 protoplasm. Whitman, on the other hand, holds this homogeneous 



