362 BERTKAM G. SMITH 



sufficient water to allow the eggs to rotate slowly until the animal 

 pole was uppermost. Eighteen eggs survived to the gastrula 

 stage. Figure 1 shows the direction of the principal axis of 

 each embryo in the advanced gastrula stage; it is evident that 

 there is no preponderance of any particular direction. So far as 

 it goes, this experiment indicates that gravity acting on the egg 



Fig. 1 Digrams showing the results of an experiment to test the possible 

 influence of gravity in determining the direction of the median plane of the 

 embryo of Cryptobranchus allegheniensis. The newly fertilized eggs were placed 

 with their polar axes in a horizontal position and parallel to each other; the 

 animal pole was directed away from the observer (i.e., toward the top of the page 

 in the figure). After the absorption of water by the envelopes, each egg rotated 

 slowly, in response to gravity, through 90° in such a manner as to bring the 

 animal pole uppermost. The diagrams show the eggs in polar view at the time of 

 gastrulation ; the arrow, pointing anteriorly, indicates the direction of the median 

 plane of the gastrula. 



immediately after fertilization is not a factor of any importance 

 in determining the direction of the median plane of the embryo. 



B. The entrance-'path of the spermatozoon 



Various observations indicate that penetration by the sperma- 

 tozoon induces profound cytological changes in the egg. In a 

 previous paper (Smith, '12, I, figs. 7 to 12) I have described 

 certain external phenomena consequent upon the entrance of 



