EMBRYOLOGY OF CRYPTOBRANCHUS 465 



Cryptobranchus japonicus; his material was meager and lacked 

 first and second cleavage stages. He states ('05) that in the five 

 eggs examined in the third cleavage stage, all the third furrows 

 are approximately meridional. His figures ('04) represent the 

 third furrows departing most frequently from the first cleavage 

 furrow, sometimes from the second, sometimes from the animal 

 pole. In the urodele Hynobius (Kunitomo '10) the cleavage 

 pattern in this stage resembles that of Cryptobranchus alleghe- 

 niensis, except that the third furrows do not so often depart fiom 

 the second furrow. In Amia, Whitman and Eycleshymer ('97) 

 describe the third cleavage furrow as follows : 



In the majority of cases they are vertical .... They gen- 

 erally all depart from one or the other of the first two meridionals, thus 

 giving rise to a distinct bilateral appearance .... It oftens 

 occurs that one or more of the set depart from the first meridional, 

 while the rest depart from the second, or vice versa. 



Stage 4: (figs. 73 to 84 and 207 to 209). This stage is charac- 

 terized by the appearance of the fourth cleavage furrows, giving, 

 when complete, sixteen cells. As will appear from the following 

 observations, the number of micromeres is not constant, but 

 varies from four to eight. 



The fourth cleavage furrows appear about four hours after 

 the beginning of the third, and about thirty-nine hours after 

 fertilization. Ordinarily they begin as two grooves, cutting the 

 first cleavage furrow at right angles', on each side of the second 

 and a short distance from it (figs. 73 and 74). Thus in position 

 and direction the fourth cleavage furrows alternate with the 

 third, which cut the second at approximately right angles. The 

 fourth cleavage is the first one to cut off micromeres from macro- 

 meres, and the division is very unequal. 



In a given lot of eggs the sixteen-cell stage is reached quite 

 uniformly at the same time, but with so much variation in the 

 direction of the fourth cleavage furrows that at first sight no 

 uniformity is recognizable. By the study of a large number of 

 eggs the following generalizations are established: 



(a) In each quadrant, one macromere is cut off between the 

 first and second cleavage furrows, giving in each egg a minimum 

 of four micromeres (fig. 74). 



