BILATERALITY IN CRYPTOBRANCHUS 365 



large part to the removal of the envelopes, for it is comparatively 

 easy to secure artificial fertilization and normal development 

 when the envelopes are not removed. Excessive polyspermy, to 

 which the eggs are peculiarly exposed after the removal of their 

 envelopes, may account for many cases of abnormal development 

 or failure to develop. In order to control the direction of fertili- 

 zation it is necessary to apply the seminal fluid at some distance 

 from the center of the blastodisc; no doubt it often happened that 

 the spermatozoon entered the egg too far from the animal pole, 

 and was unable to penetrate the yolk in order to reach the egg- 

 nucleus. In order to obtain results from a sufficient number of 

 eggs, the work was carried on each breeding season for five years. 

 Over three hundred eggs were subjected to this experiment; the 

 number does not include eggs that were rejected at once because 

 of obvious inaccuracy in the control of the direction of applica- 

 tion of the spermatozoa. 



1. Relation to the plane of first cleavage. Forty-eight eggs 

 segmented in a normal manner; in these eggs the direction of 

 first cleavage with reference to the probable direction of entrance 

 of the effective spermatozoon is shown in figure 2. It is evident 

 that there is a decided tendency for the first cleavage furrow to 

 come in approximately at right angles to the entrance-path of the 

 spermatozoon. 



2. Relation to the median plane of the gastrula. Sixteen eggs 

 survived to form normal gastrulae. In these eggs the relation of 

 the median plane of the gastrula to the probable direction of 

 the entrance-path of the spermatozoon is shown in figure 3. 

 The results indicate that there is no uniformity in the relation 

 between the entrance-point of the spermatozoon and the plane of 

 bilateral synametry of the gastrula. 



In interpreting the data, a sUght compUcation arises from the 

 fact that these eggs which survived to the gastrula stage included 

 nearly all those exceptional cases in which the first cleavage 

 furrow departed from the general rule of forming approximately 

 at right angles to the direction of application of the seminal 

 fluid. As an aid in studying this aspect of the situation, the direc- 

 tion of first cleavage in each egg is indicated in the diagram. If 



