MUSEUM OF COMPARATIVE ZOOLOGY. 479 



brace nucleoli which become visible by the use of reagents. The nuclei 

 fuse and thus give rise to the "nucleus secondaire, c'est-a-dire au nucleus 

 du vitellus feconde et debarrasse des matieres de rebut." The source of 

 the second nucleus remained unknown to Fol, as clearly follows from 

 what is said at p. 144 : " From all these references, added to the results 

 of my own observations, it appears to follow that the vitellus possesses 

 after fecundation a central nucleus the origin of which is unknown." 



I have not had access to the original paper by Giard ('76), but accord- 

 ing to R. Hertwig's abstract Giard ('76') defines fecundation to be a 

 copulation of the amoeba (or amoebae) which is formed by the penetra- 

 tion of spermatozoa into the egg, with the egg amoeba which at this 

 moment relinquishes its encysted condition (disappearance of the germi- 

 native vesicle). 



In a rabbit killed twelve hours after coitus, but not studied till ten 

 hours later, — the sexual organs having been maintained at a tempera- 

 ture not above 19° C., — Campana ('77) found some spermatozoa fixed in 

 the superficial layer of the vitellus, and two still actively swimming 

 about in the perivitelline fluid. (!) 



Fol ('77) confirms 0. Hertwig's observations of the penetration of a 

 spermatozoon into the vitellus ; the body of the spermatozoon appears 

 to fuse with the vitelline protoplasm to form a clear spot, which becomes 

 the centre of a system of radial striae. This Fol calls the male pronucleus. 

 He also reports similar discoveries for other animals. In Sagitta and 

 various Gasteropoda there is formed at the moment when the polar glob- 

 ules appear, and at the opposite pole of the yolk, a clear spot, surrounded, 

 in the case of Sagitta, with a star of protoplasmic filaments. This spot 

 moves toward the female pronucleus. During this motion one sees 

 very distinctly that the centre of the star is in advance of the clear spot, 

 and that the latter is drawn along in a passive manner. The female 

 pronucleus remains stationary till the clear spot is near at hand ; it is 

 then attracted toward it, and the latter at the same time moves more 

 rapidly. The female pronucleus and the clear spot fuse to form the 

 nucleus of the fecundated egg. The direct evidence is wanting, but to 

 judge by analogy the clear spot is a male pronucleus. 



This communication is particidarly important, since it directs attention 

 to the relation of a pronucleus to its aster. I can to a certain extent 

 confirm this observation for Limax (see Fig. 68). It is of further interest 

 because it presents so just an estimate of the composition of the polar 

 globules. Still, the idea of their formation by a process of cell division 

 can hardly be said to have been fully grasped, to say nothing of the 



