EMBRYOLOGY OF CRYPTOBRANCHUS 



461 



Comparison with the second cleavage of Necturus as figured 

 by Eycleshymer ('04), Eycleshymer and Wilson ('10), and in 

 some unpublished drawings of the living egg by Prof. Bashford 

 Dean, leads to the conclusion that in Necturus there is much 

 greater irregularity in the second cleavage than in Crypto- 

 branchus. 



Stage S: (figs. 65 to 72 and 206). The third cleavage furrows 

 appear about five hours after the beginning of the second; hence 

 the interval is shorter than that between the first and second. 

 At the time when the third furrows begin, the first furrow has 

 usually reached or passed the equator. 



65 



66 



I 3 



I 3 



Figs. 65 to 72 Types of third cleavage of Crytobranchus allegheniensis. All 

 the figures are of the upper hemisphere except figure 66 which represents the lower 

 hemisphere of the egg shown in figure 65. In no case does any cleavage furrow 

 except the first reach the lower pole. All the figures are camera drawings of pre- 

 served material. X 3|. 



As the cleavage furrows invade the more heavily yolk-laden 

 lower hemisphere they become comparatively faint except at 

 their extreme lower ends where they broaden out. During this 

 stage the second and third cleavage furrows are in general broader 

 than the first. 



4-t the stage represented in figure 65, when the third furrows 

 are well established but extend only a short distance from their 



JOURNAL OP MORPHOLOGY. VOL. 23, NO. 3 



