560 • BULLETIN OF THE 



He has summarized his own results nearly as follows : — 



1. The first sign of evolution seen in the mature egg just arrived in the 

 diverticulum, where it is fecundated, is a peculiar cloudiness of the germina- 

 tive spot and the appearance of two small " nucleoles " in it. 



2. The spot becomes diffluent, and difficult to perceive. The gerniinative 

 vesicle tends to dissolution. 



3. In the protoplasm of the nearly or entirely vanished vesicle there ap- 

 pears a double star resulting from the liberation of the two " nucleoles " from 

 the disintegrated spot. The first system of radiations u thus established. 



4. Meanwhile protoplasmic expansions arise from the surface of the yolk. 

 It is not easy to comprehend their import. After a time, they re-enter the 

 vitellus. 



5. The rays extend and promptly reach the limits of the clear space left by 

 the vanished vesicle, and invade more or less the vitelline mass itself. 



6. There always exist at the centres of radiation small nuclei (noyaux), — 

 the enlarged " nucleoles " of the germinative spot. 



7. When these nuclei have attained a certain size and a vesicular wall, their 

 vital energy, as well as the attraction which they exert on the surrounding pro- 

 toplasm, diminishes. 



8. The radiate substance then loses its consistency, becomes more fluid, and 

 is expelled in two successive drops by the pressure of the surrounding vitellus. 

 Thus the two polar globules are formed. 



9. Neither the stars nor the spindle as such take a direct part in the forma- 

 tion of the polar globules. 



10. These bodies elevate at the surface of the yolk a fine membrane, thus 

 demonstrating that a vitelline membrane exists. 



11. After tbe formation of the polar globules the double system of radia- 

 tions is no longer present ; the two nuclei previously located at their centres 

 lie in the yolk destitute of " aureola." Their volume has increased. 



12. Since these nuclei have the same origin, directly from the germinative 

 spot, one of them cannot be considered as a spermatic nucleus. 



13. The two nuclei continue to grow, and their " nucleoles " subdivide by 

 an irregular cleavage until reduced to a multitude of fine granules. 



14. The conjugation of the two nuclei is far from being demonstrated. 



15. It is more probable that one of the two is totally destroyed, and that the 

 other persists as vitelline nucleus, to give rise to two " nucleoles," which be- 

 come the centres of a new radial system embracing the whole extent of the 

 vitelline mass, and determining the segmentation. 



It will be seen that, although basing our conclusions on the study of very 

 nearly related mollusks, we are in agreement in few particulars. This may in 

 part be explained, I think, by the fact that Perez seems to have made very 

 limited use of reagents, especially in certain stages. 



As I have not traced the origin of the first archiamphiaster, it will perhaps 

 appear out of place for me to off'er any criticism of the account given by 

 Perez. If, however, it be granted that the stars of the first segmentation am- 



