EMBRYOLOGY OF CLEPSINE. 351 



the membrane, on the other hand " (tVt)- Notwithstanding 

 then the complete dissolution of the entire germinal vesicle, it is 

 regarded as " probable " that between it and the polar globules 

 a genetic connection exists, precisely as in the rabbit. How van 

 Beneden can believe that such a connection is probable in the 

 one case (polar globules) and impossible in the other (embryonic 

 nucleus), is quite incomprehensible. 



I have succeeded, I believe, in making evident a direct histo- 

 logical continuity, in Clepsine, between the germinal vesicle and 

 the cleavage-nucleus. Biitschli and Hertwig have done the 

 same for Nephelis. The same genetic bond has been traced by 

 Biitschli in Nematoids and Molluscs, and by Hertwig and Fol 

 for Echinoderms. I have not been able to determine the origin 

 of the male pronucleus in Clepsine, and Hertwig failed to produce 

 the positive proof for his theory of its origin in Toxopneustes. 



This positive proof, however, is no longer wanting, thanks to 

 the successful researches of the distinguished naturalist of 

 Geneva. Eol's discoveries confirm in the most positive and 

 decisive manner the opinion of Hertwig; and, as they fill up 

 the gap in my own observations, deserve special notice in this 

 connection. A brief account of his study in Echinus and Aste- 

 rias, which will appear in a large memoir before this paper goes 

 to press, has been given in several papers, published in the first 

 half of 1877, in the ' Coinptes rendus,' and in ' Arch, des Sci. de 

 la Bibliotheque univcrselle'' (32, 33, 34, 35, 80). In order to 

 follow the process of fecundation from tlie moment when the 

 spermatozoa first come in contact with the eggs, Dr. Eol placed a 

 drop of water containing spermatozoa on tlie object-glass of his 

 compressorium, and another drop containing the eggs on the 

 under surface of the ccver of the same. The two parts of the 

 compressorium were adjusted under the microscope, so that the 

 moment of contact was under perfect control. These precau- 

 tions remove many doubts that might otherwise arise in regard 

 to the value and importance of these investigations. 



As the cover of the instrument is pressed down, the two 

 drops of water are brought together. The spermatozoa approach 

 the egg and apply their heads to its gelatinous envelope. Soon 

 one of them plunges deeper, and by the time it has pa^sed 

 through half the tiie thickness of the envelope, a small disc of 

 transparent substance forms in the surface of the vitellus. The 

 centre of this disc soon shows a rounded protuberance (" bosse 

 hyalin "), which, rising higher, assumes the form of a cone, 

 from the apex of which a filament of protoplasm rises to meet 

 the spermatozoon. As the sperinntozoon advances it become-: 

 more and more indistinct, apparently fusing with the substance 

 of the cone which sinks into the surface of the vitellus. At 



