No. 2.] THE DEVELOPMENT OF THE NEWT. 313 



male and female elements busy themselves during this period 

 more in preparation for union than in actual movement. It is 

 even fair to suppose that speedier metamorphosis of the nuclei 

 would imply — or, perhaps, cause — greater rapidity of move- 

 ment. This indeed is indicated by the course of the phenomena 

 in the frog's Q^^g where the course of events is more rapid. 

 The hindering effect of the yolk must be practically the same 

 in both cases, and one is justified therefore in regarding the 

 slower movement of the male element in the newt's q^%% as the 

 expression of a slower maturation of that element. In other 

 words it is not the external obstacles, but the internal changes 

 that determine the rate at which the two pronuclei approach 

 each other. 



The path taken by the sperm is similar to that de- 

 scribed by Roux ('87) for the frog's ovum. The spermatozoon 

 moves at first centripetally, describing the "penetration-path," 

 and later describing the "copulation-path," curves more or less 

 abruptly towards the female pronucleus. The initial change 

 from the centripetal to the nucleopetal direction is shown in 

 Figs. 23C and 23D. It is impossible not to agree with those 

 who hold that this change in direction is due to some sort of 

 nuclear attraction. 



The female element, which is the objective point of the male 

 pronucleus and is hence the cause of the change of direction 

 of the latter, is by no means a mere inactive spectator of the 

 entrance of the spermatozoon. About two hours after the Qgg 

 is laid the polar body (second .'') is expelled (Fig. 20). It is clear 

 that this expulsion of the polar body is caused directly by the 

 penetration of the sperm into the &gg, since before this event 

 the female element has remained perfectly passive, it may be 

 for upwards of forty-eight hours. The nature of this telepathic 

 influence is far from clear. After this event the female pro- 

 nucleus is formed by a series of changes which I have not been 

 able to trace out completely, but which appear to be essentially 

 parallel to those of the sperm. Indeed I have been in most 

 cases unable to distinguish between the male and female pro- 

 nucleus after the formation of the latter. This is owing partly 

 to the fact that the male pronuclei are usually numerous, partly 



