Miscellaneous. 157 



about midway ; a fifth joined these, and then, after a few wrigglings, 

 disengaged itself and disappeared. 



I watched persistently the two spermatozoids that adhered to the 

 apex of the little elevation ; and my eye did not miss them for a 

 moment. Their two bodies, laid side by side, always remained at 

 the surface of the ovum ; and their tails were to be seen extended in 

 the course which they had followed. Soon the vitelline membrane 

 detached itself from the vitellus, and the projection ceased to exist ; 

 bat the two spermatozoids were still to be seen, elevated with the 

 membrane, and quickly conveyed by it to a great distance from the 

 yelk. The ovum was fecundated ; but no spermatozoid had pene- 

 trated into its interior. 



One remark will be useful. In this observation the plane of 

 vision passed through the centre of the ovum ; and the protuberance 

 was exactly in this plane, at the equator of the ovum. If one of 

 the spermatozoids had carried its body a little higher or a little 

 lower by creeping upon the slope of the projection, this body, pro- 

 jected upon the latter, woidd have disappeared, whilst the tail might 

 have remained visible beyond. In this way we should have the 

 exact image of a spermatozoid penetrating into the ovum and leaving 

 its tail out, just as M. Fol states he observed it. 



The rising of an eminence at the surface of the ovum, in ray 

 opinion, has no connexion with fecundation. It is a simple acci- 

 dent which depends solely upon a solution of continuity in the 

 mucous envelope (which is very freijuent at least in the sea-urchin), 

 constituting a point of weakest resistance at the surface of the 

 ovum, and, in consequence, a corresponding deformation of the 

 vitelline sphere. It will thus be understood why, of all the points 

 of this sphere, the deformed part, when one exists, is usually the 

 first attacked by the spermatic filaments. This deformation, reduced 

 to a slight prominence in the case described by M. Fol and in that 

 above mentioned by me, sometimes acquires exaggerated proportions, 

 which, however, have no injurious eff'ect upon the fecundation. 



More than this, the penetration, as understood by M. Fol, clashes 

 with an anatomical impossibility. That naturalist assumes, in fact, 

 that the unfecundated ovum is destitute of vitelline membrane, and 

 that this envelope originates only under the influence of fecunda- 

 tion. Now it is iucontestaljle that it exists even in the very young 

 ovum while the latter is still not granular : in this it is easy to ob- 

 serve it directly ; and the ondosmotic action of pure water renders it 

 still more evident. In the mature but unfecundated ovum of the 

 Echinns a slight pressure, which clears its contents, suffices to show 

 all round it a continuous uniform envelope, with a double coiitour, 

 contrasting by its refringency and its orange-rose colour with the 

 subjacent vitellus. It measures about -rofirnT raillim. in thickness. 

 AVhen subsequently distended and removed from the vitellus, in 

 consequence of impregnation, it becomes thinner and paler. The 

 act of t'eciindation, therefore, does not determine the formation of 

 the vitelline membrane, which existed long before ; as regards this 



