360 BERTRAM G. SMITH 



In nature, the developing egg of Cryptobranchus is shielded 

 from the Ught; the factor of pressure also is negligible. In 

 experimental procedure these factors are best dealt with by elimi- 

 nating them so far as possible from the conditions of the experi- 

 ment. The only external influence that appears to be normally 

 related to the life of the egg, in such a way that it might affect 

 bilateral symmetry, is gravity. So long as the eggs are retained 

 in the body of the female their orientation is variable and incon- 

 stant, but since there is comparatively little axial differentiation 

 during this period, it is not Ukely that even under the most 

 favorable conditions of orientation could gravity exert any 

 appreciable influence on the organization of the egg. If the egg 

 is at all susceptible to the influence of gravity in determining the 

 direction of the median plane, the most favorable conditions are 

 presented immediately after spawning and fertilization. At this 

 time the cytoplasm accumulates rapidly about the animal pole. 

 The newly laid egg is closely invested by the gelatinous envelope, 

 and does not freely orient itself with the animal pole uppermost 

 until after sufficient water has been absorbed to cause the capsule 

 to become turgid and spring away from the egg — a process re- 

 quiring from one to two hours. During this period, in which 

 the polar axis may make any angle with the vertical, gravity 

 might possibly rearrange the contents of the egg in such a way 

 as to affect the direction of the median plane of the future embryo. 



EXPERIMENTS AND OBSERVATIONS 



All the experiments with living material were carried out in 

 a cellar, where the temperature was favorable for the develop- 

 ment of the eggs and the light could be controlled. So far as 

 possible the eggs were shielded from the light ; they were handled 

 as gently as possible to avoid the disturbing effects of mechanical 

 manipulation. 



Some of the experiments about to be described involve placing 

 the egg in a definite position and keeping it there for a considera- 

 ble period of time. Trials of various methods showed that it is 

 sufficient and most expedient to orient each egg in water in a 

 separate watch-glass and leave it in a situation where it will not 



