MUSEUM OF COMPARATIVE ZOOLOGY. 489 



tozoa, moreover, are allowed to a single egg. The protuberance which 

 Perez has seen is not at all the hyaline cone, but is a granular projection 

 of the yolk of considerable size. Corresponding to the point of attach- 

 ment of the ovule there is an interruption in the continuity of the mucous 

 envelope, and into this the yolk often penetrates. This protuberance 

 is wanting in eggs near to exclusion. In the sea-urchins the process of 

 penetration is much more rapid than in the starfishes, and there is ?io 

 hyaline protuberance formed in this case. Hence the error attributed to 

 the author by Perez is impossible, as regards the sea-urchins at least. 



The pre-existence of a vitelline membrane is disproved by the author's 

 preparations, still preserved ; for when the polar globules are formed after 

 fecundation, they are found to be within the vitelline membrane, but 

 when before fecundation they are outside of that membrane. Fol does 

 not deny the existence of a limiting envelope at the surface of the ovule 

 in starfishes and sea-urchins, but it is soft and plastic, like the limiting 

 layer of an Amoeba. One can make of it a membrane by coagulating 

 the organism. This layer normally becomes a membrane only at the very 

 moment of fecundation. 



Perez ('77") is still unable to admit an attraction exercised " a dis- 

 tance" by the spermatozoon, for he has observed in the case of the 

 sea-urchin Fol's "cone d'exsudation " before as well as after the approach 

 of spermatozoa, up to the time when the elevation of the vitelline mem- 

 brane and the expansion of the mucous layer have caused it to disappear; 

 but he regards it (the cone) as the optical projection of the walls of the 

 opening which constitutes the interruption in the continuity of the 

 mucous layer. The " soft and plastic layer " of the vitellus cannot be 

 compared to the envelope of the Amoeba, since the spermatozoa after 

 traversing the mucous layer meet here an impenetrable obstacle. 



GiARD ('77*) does not recognize the " necessity of employing sperma- 

 tozoa in homoeopathic doses," since those conditions are not realized in 

 nature, nor does he understand how it is that Fol depicts eleven sperma- 

 tozoa on a limited portion of the surface of an egg, if in his experiments 

 he allows to each only three or four spermatozoa. From 10 to 15% of 

 the eggs he himself has studied present pathological peculiarities, among 

 which are not included cases of the formation of a tetraster, which he 

 considers due to an ontogenetic abbreviation, not resulting in monsters, 

 and comparable with Strasburger's observations on gymnosperms. Fol's 

 statement that the sea-urchins present no hyaline protuberance is cer- 

 tainly not applicable to Psammechinus, where this protuberance is to be 

 seen with the greatest ease. If Fol's view concerning the vitelline mem- 



