EMBRYOLOGY OF CRYPTOBRANCHUS 



459 



variation, sixty eggs from a single spawning were examined in 

 the first cleavage stage. In forty-eight cases the condition was 

 of the typical character described above. In seven cases the 

 first cleavage furrow was straight, but the cleavage unequal; 

 figure 58 represents the extreme of this condition. In three 

 cases, the first cleavage furrow passed through the animal pole, 

 but its halves met at this pole to form an obtuse angle (fig. 59). 



57 



58 



60 



6) 62 6ci 64 



Figs. 57 to 64 Types of first and second cleavage of Cryptobranchus alle- 

 gheniensis. X 3|. 



Fig. 57 The first cleavage furrow extends just to the equator, a little further 

 than is usual before the appearance of the second furrow. 



Fig. 62 The first cleavage furrow extends a little below the equator. 



Fig. 64 The first cleavage furrow extends a little below the equator; the second 

 furrow extends just to the equator. 



In two cases the first cleavage furrow formed a semicircle about 

 the animal pole (fig. 60) . In two cases from different spawnings, 

 neither of which furnished the material for the above data, cir- 

 cular first cleavage (fig. 61) was found; in each case the animal 

 pole was excentrically situated within the area bounded by the 

 cleavage furrow. 



Goodale ('11) reports a case of circular first cleavage in Spe- 

 lerpes; the egg gave rise to a normal embryo. According to 

 Eycleshymer ('04), in Necturus the cytoplasm is always unequally 

 divided by the first cleavage, giving rise to blastomeres which 

 in many cases are decidedly unequal. 



