MUSEUM OF COMPARATIVE ZOOLOGY. 461 



archiamphiaster is already formed at the time of extrusion, and usually 

 has a radial position with one pole so near the surface that it gives rise 

 to a "polar figure" visible on the living egg as a white spot with dis- 

 tinct radial structure. After the archiamphiaster is formed, the egg, 

 provided it is not extruded and brought in contact with water, may 

 remain in a quiescent condition for at least two (or perhaps for even 

 four or five) days, without any injury or abnormal effect upon its 

 development. Thpre appears in the centre of the " polar figure " about 

 half an hour after extrusion a minute pellucid spot which is entirely free 

 from yolk spheres and granules. This is the central part of the polar 

 area of the outer star, and is deeply stained in carmine. I have else- 

 where (p. 421) alluded to the significance of this pellucid spot. Although 

 the subject is not formally discussed by the author, it seems to me that 

 he leaves the impression that he regards this polar corpuscle " C. P. " as 

 the beginning of the new nucleus. At least, he says, a similar " pellucid 

 spot " is seen immediately after the formation of the second polar glob- 

 ule, and marks the place of its exit (p. 20). A section of the egg at this 

 time shows beneath the globules a circular space free from deutoplasm, 

 open toward the globules, and filled with a very fine granular substance, 

 which has the lead-gray tinge characteristic of the germinative vesicle 

 that has been treated with osmic acid. This body, which appears as a 

 pellucid spot on fresh eggs and which may be designated with Van Bene- 

 den and Fol as female pronucleus, says Whitman, is the remnant of 

 the archiamphiaster. Thus indirectly we may infer, I think, that the 

 first-mentioned "pellucid spot" was estimated by him to be a nuclear 

 structure. As far as I can judge by comparison with other objects, I 

 am inclined to think that no part of the Kernplatte is embraced in these 

 pellucid spots. I am not so confident that no part of this areal corpus- 

 cle enters into the composition of the female pronucleus in the case of 

 Clepsine. To judge from what takes place in Limax, it is to be ex- 

 pected that this corpuscle in the polar cells, at least, takes no part 

 whatever in the nuclear structure. If it shall hereafter be possible at 

 any time to trace the fate of the Kernplatte, the question may be defi- 

 nitely settled ; till then I can only believe that there is no essential 

 variation in Clepsine from what I have seen in Limax. 



The formation of the polar globules in C. marginata is accompanied 

 by a very interesting change in the form of the egg, first observed by 

 Whitman. About thirty minutes after extrusion a marked constriction 

 of the egg at the equator becomes visible ; this constriction without be- 

 coming very deep advaftces slowly and uniformly toward the pole where 



