MODIFICATION OF THE GERM-CELLS IN MAMMALS 195 



than the ova. The inferiority of the column from male ances- 

 tors treated as compared with that from female ancestors treated 

 in the second group of table 4 seems to substantiate such a 

 position. The possibility exists, however, that the treatments 

 of the male and female ancestors may not have been equally 

 severe, since they have been treated in different fume tanks. 

 This question is now being studied. At any rate, we believe it 

 is proved that the germ cells of the female are as definitely in- 

 jured and modified by the treatment as are the germ cells of the 

 male. This is the point of importance in the present connection. 



The female offspring from treated fathers were found in the 

 report cited to be inferior as a group to the male offspring as 

 regards their powers of existence and structural perfection. The 

 opposite was indicated among the offspring of treated mothers, 

 the males being inferior to the females. Our explanation of 

 these conditions was that the two classes of spermatozoa which 

 differ structurally also differ in the degrees of injury suffered 

 from the treatment. We are further testing these suppositions 

 by selected matings and hope to report on them in the future. 

 For further details regarding the supposed differences between 

 the behavior of the two classes of spermatozoa, the reader is 

 referred to. our 1916 paper. 



An explanation of the sex-ratios in table 6 may now be given 

 along similar lines and the peculiarities found among these sex- 

 ratios are exactly in accord with our previous theoretical consid- 

 erations. If the male guinea-pig does possess, as has been claimed 

 (Stevens, '11), heteromorphic spermatozoa, one class with a 

 small Y chromosome, the male producing, and the other class 

 with a larger X chromosome, the female producing, the follow- 

 ing may be assumed: In the treated-male lines the female-pro- 

 ducing spermatozoa are more decidedly affected, possibly on 

 account of their larger quantity of chromatin, and therefore, in 

 the competition to fertilize the eggs they are not so successful 

 as the less injured male-producing sperms. Consequently, more 

 male animals are produced than female. Or, if the female- 

 producing sperm are not in any or all cases actually prevented 

 from fertilizing eggs, nevertheless the individuals produced by 



