324 JORDAN. [Vol. VIII. 



frog, namely that the path of meeting of the male and female 

 pronuclei defines the first plane of cleavage. In the newt we 

 should have to suppose, to uphold this theory, that the pathway 

 was always coincident with the median transverse axis of the 

 capsule. Since the point of entrance of the spermatozoon is 

 indeterminate this supposition of an invariable pathway of 

 approach is not justified. Furthermore, since several sperma- 

 tozoa normally enter the egg there are several pathways in 

 different directions, and some of the spermatozoa travel a 

 greater distance through the egg-substance than does the 

 spermatozoon that unites with the female pronucleus. The 

 sundering of the egg-substance may therefore be of greater 

 extent along the path of an unsuccessful sperm-nucleus than 

 along that of the " Hauptspermakern." It is obvious, then, 

 that Roux's explanation of the direction of the first cleavage 

 plane, however valid it may be for the Q.g^ of the frog, does not 

 admit of application to the egg of the newt, and that here we 

 must seek for some determining cause other than the path 

 taken by the male and female pronuclei 



As regards Schultze's view that the first cleavage plane is 

 determined by the position of the germinal vesicle in the 

 unfertilized ovum I must agree with Roux in considering 

 the evidence for such a view inadequate. 



In the case of the newt the very tempting explanation 

 suggests itself that the direction of the first cleavage plane 

 is due to the compression and elongation to which the Q.^g 

 has been subjected in the oviduct. It may be legitimately 

 maintained that the arrangement of the ^gg substance has 

 been so affected by this compression that the first spindle 

 can place itself with its long axis parallel to the elongated 

 axis of the ^gg more readily than it can in any other axis. 

 In other words the spindle takes the direction that it does 

 because the ^gg has been elongated in that direction. 



Another slightly different explanation of a similar mechanical 

 nature is perhaps still more plausible. The Qgg soon after 

 it is laid resumes its spherical form and is then in close 

 contact with the capsule on all sides except in the direction 

 of the long axis of the capsule. In this direction there is 



