354 Miscellaneous. 



the fecundated ovum. These phenomena singularly resemble those 

 observed by M. 0. Hertwig and myself in the K-hinus. If I were to 

 judge of them by analog}-, I should say that the clear spot with its 

 star is the male pronucleus ; but I have no direct proof of this. MM. 

 Auerbach and Biitschli have already observed this movement of the 

 two vesicles starting from the two opposite poles of the vitellus to 

 become fused together ; but M. Auerbach did not perceive that 

 these phenomena only take place after the issue of the polar cor- 

 puscles, and M. Biitschli confounds the fusion of the two pronuclei 

 with the amalgamation of the various vacuoles which constitute 

 the female pronucleus. 



In Asterias, according to the observations of MM. R. Greef, E. 

 van Bcneden, and myself, and in the Gasteropoda, the Purkinjean 

 spot dissolves in the germinal vesicle, which in its turn disappears 

 to give place to a double star, which has already been observed by 

 M. BiitschH. 



Here we have two distinct cases ; and I add a third. In Denta- 

 lium, according to M. Lacaze-Duthiei'S, the polar corpuscles effect 

 their escape even before the ovum is fecundated ; and in Asterias, 

 according to M. R. Greef, the germinal spot and vesicle disappear in 

 the deposited but not fecundated ovum, and the parthenogenetic 

 development of the Starfish only differs by its slowness from the 

 development of the fecundated ovum. M. K. Greef did not observe 

 the formation of two pronuclei ; but I have seen them in the fecun- 

 dated ova of Asterias. 



Seeking a clue to the interpretation of all these data, we are led to 

 distinguish, in the first place, two well marked cases. In the first 

 case, which is that of EcMnus, the ovule, at the moment of its de- 

 position, is already destitute of its germinal vesicle, and only pos- 

 sesses a female pronucleus ; this becomes, fused, in consequence of 

 fecundation, with a male pronucleus containing the substance of the 

 spermatozoid; and development takes place without previous expul- 

 sion of polar corpuscles. In the second case, which is that of the 

 great majority of animals, the ovule, when deposited, still possesses 

 a germinal vesicle and often a germinal spot. These two elements 

 disappear, and the greater part of their substance is expelled from 

 the vitellus in the form of corpuscles, the remainder entering 

 into the composition of a female pronucleus. In the ova which are 

 developed by parthenogenesis, it would appear that this female pro- 

 nucleus plays the part of a nucleus, and segmentation commences. 

 In the fecimdated ova there is formed, at the pole opposite to that 

 at which the female pronucleus is situated, a second pronucleus, 

 which I believe may be regarded as containing the substance of the 

 spermatozoid. These two pronuclei fuse together and the segmen- 

 tation commences. The principal difference between these two 

 cases would therefore consist in the earlier or later period of the 

 disappearance of the germinal vesicle. 



MM. E. van Beneden and Biitschli have already attempted to 

 reduce all these phenomena to a common scheme, but without taking 



