468 BULLETIN OF THE 



subsequently begin depend upon the same cause (not yet fully under- 

 stood), — a cause which effects the segregation of the more active con- 

 stituents of the egg about the pole in question before either of these 

 phenomena have taken formal expression. 



Blanchard pertinently objects to Rabl's theory of the protective office 

 of the polar globules, on the ground that, if injurious pressure were 

 exerted by the egg membrane, the globules would only serve to increase 

 its damaging effect by concentrating the pressure upon a more limited 

 extent of the embryo's surface, and thereby necessarily increasing pro- 

 portionally the intensity of the pressure. 



3. Fecundation. 



It is my purpose to review such papers as treat the subject of fecun- 

 dation in the light of the recent discoveries of nuclear copulation, or such 

 as have paved the way to so fundamentally important a conception of 

 the nature of the process in question. The order in which these phe- 

 nomena have been discovered has been nearly the reverse of the succes- 

 sion in which the events of fecundation make their appearance. It was 

 in the earlier part of the present decade that a beginning was made in 

 divesting the later stages of fecundation of some of their mysteries, and 

 only by a sort of retrogressive exploration that we have within the past 

 two or three years come to understand better the earlier stages of the 

 process, and to put all in more satisfactory correlation. 



BiJTSCHLi ('73") was one of the earliest observers to trace some of the 

 changes which overtake the pronuclei, but he could give no account of 

 their origin, and therefore had no idea that they were intimately con- 

 nected with the fecundation of the egg, as he also was in doubt about 

 their actual coalescence. His account of the phenomena accompanying 

 their union has been, for the sake of convenience, given in another 

 connection (pp. 280, 396). 



The studies of Weil ('73) I am. only acquainted with through Hof- 

 mann and Schwalbe's " Jahresbericht," etc., from which it is to be learned 

 that he has observed in rabbit eggs taken from the oviduct between 

 seventeen and forty-six hours after fecundation (should probably read 

 " after copulation ") living spermatozoa, in four cases within the egg 

 protoplasm itself. Like Van Beneden, Weil also saw two nuclei (male 

 and female pronuclei) before the beginning of segmentation. 



What has already been said of the origin of the female pronucleus, as 

 described by Auerbach, is true of the male pronucleus. Concerning the 

 further changes of the pronuclei after they meet in the centre of the 



