408 BULLETIN OF THE 



The main objection to this view is the fact that no other complete aster, 

 and no indication of another nuclear structure which might be the female 

 pronucleus, is made to appear in this figure. I can only assume that the 

 latter was overlooked. 



As the ovarian egg of Toxopneustes livid us approaches maturity it 

 contains, according to 0. Hertwig ('75, pp. 349 - 358), a large spherical 

 germinative vesicle with nuclear membrane derived from the protoplasm, 

 clear contents, and a spherical germinative dot of constant size (13 /x) 

 and homogeneous structure. The dot is deeply stained in carmine, the 

 clear contents only feebly. The two are designated as nuclear substance 

 and nuclear juice respectively. Besides these, a network of fine pale 

 fibres stretches through the vesicle, for whose membrane it forms 

 a lining, and is especially concentrated about the dot. In the mature 

 egg found in the oviduct, on the other hand, the germinative vesicle has 

 disappeared without leaving a trace, but there exists a small clear spot 

 which before was not present. The latter is spherical, and 13 /m in diam- 

 eter. Intermediate stages lead Hertwig to the conclusion that the vesi- 

 cle is expelled from the egg, that it at first lies in a lenticular depression 

 of the yolk, but afterwards becomes flattened, that its membrane is 

 dissolved and its contents become disintegrated, and probably that it 

 is subsequently absorbed by the yolk. He believes, however, that the 

 germinative dot persists without change, and either actively or passively 

 comes to occupy a position in the yolk, as the clear spot already alluded to. 

 The assumption of the identity of the germinative dot with the clear spot 

 (Eikern) is supported in the author's opinion by equality of size ; and by 

 the facts, that both consist of a tolerably firm homogeneous substance 

 without enveloping membrane; that both are stained intensely in carmine 

 and blackened in osmic acid ; that the disappearance of, or any change 

 in the dot, could not be observed, nor any steps in the formation of the 

 Eikern; that both structures are never met in the same egg, and never 

 are both absent; and, finally, that the Eikern first appears near the met- 

 amorphosed germinative vesicle, while the dot is last to be seen in imme- 

 diate contact with the surface of the yolk. The necessity of a migration 

 from the vesicle into the yolk cannot be an objection to the identity, 

 since nucleoli have often been observed in amoeboid motion. 



In a general discussion of the topic, Hertwig attempts to harmonize 

 conflicting views, or at least to explain the reasons of such differences. 

 The testimony of those who describe a regressive metamorphosis and 

 disappearance of the germinative vesicle must be accepted as valid for 

 the cases described ; the positive assertions of those who claim that the 



