206 CHARLES L. PARMENTER 



McClung ('05, '07, and '17), and others. But it is very im- 

 portant to note that these irregular chromosomes arise and 

 perpetuate themselves in a manner entirely consistent with a 

 definitely organized chromatin and furnishes no support what- 

 ever for Delia Yalle's contention that the chromosomes are 

 comparable to crystallizations of a salt solution and that their 

 number in any cell is dependent upon the law of chance. 



C. Variations in other Urodeles 



Snook and Long ('14) find in the spermatogonial cells of 

 Aneides lugubris nine containing clearly the usual number of 

 twenty-eight chromosomes, and one cell with twenty-three. 

 There are no other authentic reports of variable chromosome 

 number in individuals of the Urodeles. The counts of Kolliker 

 ('89), Fick ('93), and Jenkinson ('04) in the cleavage stages of 

 Axolotl (Ambystoma tigrinum) were made for other purposes, 

 and were not presented as accurate number determinations. 

 Likewise, the counts of about eighteen to twenty-four, Champi 

 ('13, p. 124) in several other Salamanders are only approximate. 



D. Variations in other forms 



Since a somewhat extensive tabulation of comparative germi- 

 nal and somatic counts has been made and discussed by Hoy 

 ('16), Harvey ('16), and briefly reviewed by Hance ('17 b), a 

 repetition of this discussion is of little value. However, in the 

 review of reported cases of variation a few general considerations 

 have impressed me as worthy of mention. These may seem 

 commonplace, but are evidently not altogether realized by some 

 who are none too critical in their discussion of the significance 

 of these enumerations. 1) As Montgomery ('01) long ago sug- 

 gested, it is important to distinguish between variation in the 

 chromosomes in the germinal line and those . of differentiating 

 somatic cells. In the germ cells I believe it can be stated safely 

 that there are no certainly demonstrated variations in number 

 which do not conform to a definite organization of chromatin. 

 From time to time cases of apparent variation have appeared 



