190 ROBERT T. HANCE 



in the previous work on the pig. In a study of the tissues from 

 seven mammals in connection with work on "The fixation of mam- 

 mahan chromosomes" (Hance, '17 b) the chromosomes of none of 

 the forms studied, when killed and treated in the proper way, were 

 clumped together or variable in width. They did not look like 

 amorphous lumps of stainable material ' which is the appearance 

 of many of the mammalian chromosomes in published figures. 

 Furthermore, the number was always high, in all cases about 40 

 or more. With a large amount of material from so many mam- 

 mals, I think that I have a fair basis for the criticisms I have 



. . . ' 



made of the mammalian cytological studies up to date. Wini- 

 warter's work stands out above that of other workers, if we may 

 judge the excellence of his fixation from the clearness of his 

 published figures. The diploid chromosomes he figures for the 

 cat are very comparable, in form and number, to those I have 

 found in this animal. I have already suggested ('17 b) that when 

 a study of human cytology is repeated on properly preserved 

 and freshly killed tissue, the number of chromosomes will be 

 nearer that reported by Winiwarter than by other investigators. 

 The variations in the somktic chromosome number which he 

 has found in the rabbit are very suggestive from the point of 

 view of the present work and will be considered later. Miss 

 Steven's figures of the spermatogonia of the guinea pig ('11), 

 although she found but few clear cells, appear to justify her 

 count of 56. Wieman's prophase figures, in his paper on the 

 chromosomes found in a human embryo appear considerably 

 better than do his later figures on the spermatocytes ('13 and 

 '17). Wodsedalek's figures of the chromosomes of the mule 

 ('16) are somewhat better, as regards separation, than those in 

 his papers on the horse and the pig, but all leave much to be 

 desired in the way of regularity of chromosome outline and 

 differentiation of chromosomes. , 



Reported cases of fraginentation 



The most familiar case of variation in somatic chromosome 

 number is that of Ascaris megalocephala reported by Boveri. 

 Here the fertilized egg starts with two chromosomes, and the 



