158 Miscellaneous. 



envelope, its only effect is to cause its inflation and its separation 

 from the vitellus. 



The presence of a proper membrane around the unfecundated 

 ovum of the sea-urchin seems to me to be indubitable. "We are not 

 to imagine in this case a thin layer of hyaline non-granular proto- 

 plasm presenting only the appearance of a membrane. At the first 

 glance a distinctly marked double contour renders any such inter- 

 pretation impossible. If, therefore, it be supposed that the penetra- 

 tion of the spermatozoid is indispensable for fecundation, we have 

 to inquire how it can get through such an obstacle, especially if we 

 assume that this penetration can be effected at any point of the sur- 

 face of the ovum. — Comptes Rendus, March 26, 1877, p. 620. 



On some Abnormal Fecundations in Starjislies. 

 By M. H. FoL. 



In a former note I described the modifications undergone by the 

 mature ova of Asterias glacialis when they are merely placed in 

 sea-water, and the phenomena of an artificial fecundation performed 

 with ova already freed from their polar materials. Let us now try 

 the fecundation of the ova immediately after their escape from the 

 ovary, or at least before the expulsion of the first polar corpuscle. 



The details of the penetration of the zoosperms into the vitellus 

 are very nearly the same as in the normal case. The ijrincipal dif- 

 ference is that the vitelline membrane is only very slowly formed 

 and elevated round the point where the penetration is effected ; 

 instead of rapidly gaining the whole surface of the vitellus, it only 

 extends over a portion of the periphery. Hence other spermato- 

 zoids have time to penetrate successively at different points of the 

 surface of the ovule ; and they continue to do so until the vitellus 

 is completely enclosed in a membrane impermeable to the zoo- 

 sperms. 



The extent and rapidity of formation of the portions of the mem- 

 brane which are differentiated round each point of penetration are 

 very variable, and are less in proportion as the normal conditions 

 are more widely departed from. In such cases 1 have counted as 

 many as fifteen zoosperms in a single vitellus ; and this number 

 decreases as we ojjcrate under more normal conditions. 



The body of the zoosperm fiows into the vitellus ; and at this point 

 there is formed a clear spot surrounded by radiating filaments. This 

 is the male aster. Those male asters, starting from various points 

 of the surface of the vitellus, travel slowly in the direction of its 

 centre. Except as regards the number of asteis, all this is in con- 

 formity with the normal case. If the fccimdation takes jjlace 

 before the disaiipeaiance of the germinal vesicle, the male centres 

 remain for a consideiable time in a latent state, and it is only at 

 fhe moment when the first polar corpuscle begins to issue, some- 

 times even already at the momerrt when the waste amphiaster is 



