Miscellaneous. , 155 



the two polar corpuscles in the manner so well described by M. C. 

 Robin. The use of picric acid shows the presence of an amphiaster 

 which divides in such a manner that the peripheral aster becomes 

 the first polar corpuscle ; then the interior aster changes into a new 

 amphiaster, the peripheral half of which constitutes the second polar 

 corpuscle, whilst its interior half is converted into a little spot. 

 This spot increases rapidly, at the same time advancing towards the 

 centre of the vitellus, and changes into a true pronucleus furnished 

 with one or two nucleoli. This female pronucleus stops before at- 

 taining the centre of the ovule, which now enters upon a new period 

 of inactivity. 



All the modifications that the vitellus has hitherto undergone have 

 been occasioned by the mere contact of sea-water without any fecun- 

 dation. They occur in exactly the same manner whether the ovum 

 is fecundated or not. This fact is not new ; but it needed to be 

 confirmed by repeated experiments. 



The ovule thus modified by a stay in sea- water is in the state best 

 fitted to receive fecundation. It' it is not fecundated it will remain 

 unchanged for some hours, and then begin to decompose slowly. I 

 have never seen it develop by parthenogenesis. Leaving out of 

 consideration for the moment the abnormal cases which occur when 

 the ovum is fecundated before or after the favourable moment, and 

 when it is altered in any manner, we may pass in review the phe- 

 nomena of normal fecundation. 



The spermatozoids, on coming into contact with the ovum, remain 

 with their bodies stuck into the mucous envelope. Soon one of 

 them succeeds in making its way through half the thickness of this 

 layer ; and immediately the vitellus presents some extremely re- 

 markable modifications. Before anycontact has taken place be- 

 tween the spermatozoid and the vitellus, the protoplasm of the latter 

 accumulates on the side which looks towards the nearest spermato- 

 ■ zoid, and then forms a thin hyaline layer which coats the granular 

 vitellus; then this transparent layer rises in its centre into a boss, 

 which advances to .meet the male element. The boss changes into 

 a cone ; and we soon see a delicate thread of protoplasm establish- 

 ing communication between the apex of the cone and the body of 

 the spermatozoid. The latter elongates, and, so to speak, flows into 

 the vitellus. The tail, or, we may rather say, the vibratile cilium, 

 alone remains outside, where it may be still distinguished for several 

 minutes. 



During this time the sixperficial hyaline layer gains more and 

 more in extent, and finally envelops the whole vitellus. At the 

 moment when the communication with the spermatozoid is esta- 

 blished, this layer becomes very distinctly differentiated, and begins 

 to detach itself from the surface of the vitellus to form a vitelline 

 membrane. The differentiation of this membrane gains the whole 

 circumference of the vitellus, commencing from the point of fecun- 

 dation, where there remains a sort of little crater. In a perfectly 

 mature and very fresh ovum all these phenomena succeed one ano- 

 ther with such rapidity that access to the vitellus is barred to all 



