Miscellaneous. 353 



the knowledge of these primordial phenomena. M. 0. Hertwig has 

 shown, in his fine memoii- on the first development of the Echini, 

 that the spermatozoid penetrates into the ovum, and enters into the 

 composition of the nucleus of the fecundated ovum. I have repeated 

 M. Hcrtwig's observations and can warrant their correctness, ex- 

 cepting some details which will appear from my own description. 

 The body of the spermatozoid, when it has entered the vitellus, 

 appears to amalgamate with the vitelline protoplasm to form a clear 

 spot, which becomes the centre of a system of radiating strite. For 

 this spot I adopt the term pronucleus, proposed by M. E. van Bene- 

 den ; and I shall call it the male pronucleus. This male pronucleus 

 traverses the vitelliis to mingle intimately with a female pronucleus, 

 which is situated at the moment of fecundation in the part of the 

 vitellus opposite to that through which the spermatozoid penetrates. 

 Dei'bes and M. 0. Hertwig regard this female pronucleus as iden- 

 tical with the Purkinjean spot of the ovule before its matui-ity. I 

 reserve my opinion upon this point, which T have been unable to 

 elucidate. From the fusion of these two pronuclei results the nucleus 

 of the fecundated ovum, which is afterwards segmented in the 

 manner described by me in a previous note. 



In tracing the development of the Ecliinus, one is struck by the 

 complete absence of any polar corpuscle. This evidently constitutes 

 a very exceptional case in the animal kingdom. In the immense 

 majority of cases the ripe ovule possesses a large germinal vesicle, 

 which only disappears at the moment of fecundation {i:iagitta), or a 

 little later (Pterotrachva, Asterias, &e.). This germinal vesicle is 

 immediately replaced by a system of filaments arranged in a double 

 star, absolutely as in a cell which prepares to divide, only this 

 .system is situated quite close to the surface of the ovum. The more 

 peripheral star then issues from the vitellus to constitute a polar 

 corpuscle, which may divide after its escape : most frequently it 

 remains entire, and the star remaining in the interior of the vitellus 

 divides into two stars, one of which issues to constitute the second 

 polar corpuscle. The substance expelled in this manner repre- 

 sents the greater part of the germinal vesicle enveloped by a little 

 vitelline protoplasm. The opinion of (EUacher as to the origin of 

 these corpuscles in the Trout finds a brilliant confirmation in these 

 facts. The last star that remains ia the vitellus collects to form a 

 pronucleus. 



At this moment I have observed in Sagitta and various Gastero- 

 poda a clear spot which forms at the opposite pole of the vitellus. 

 This spot is surrounded, in Sagitta, by a star of protoplasmic fila- 

 ments. It moves in the dii'ection of the spot where the other 

 pronucleus is placed. During this movement of translation we see 

 very clearly, in Sagitta, that the centre of the star occurs in front 

 of the clear spot, and that the latter is passively drawn along. On 

 its arrival close to the other pronucleus, hitherto motionless, this 

 star moves more rapidly, the pronucleus is drawn towards the clear 

 spot, and these two elements fuse together to form the nucleus of 



