MODIFICATION OF THE GERM-CELLS IN MAMMALS 179 



treated, and third, when both male and female ancestors are 

 treated with all first generation, Fi offspring, excluded. The 

 modified conditions shown by these records are due to an heredi- 

 tary transmission of the defects and not in any case to the 

 direct influence of the treatment on the developing animals. 



The fourth column from only male ancestors when compared 

 with the normal stock in tables 1 and 2 shows a higher 'early 

 prenatal mortality' based on the average litter size and high 

 number of mating failures, a lower average litter weight, a higher 

 late prenatal mortality, and a higher total mortality. The re- 

 sults of these matings are, therefore, from any point of view 

 worse than the results of normal matings. And they prove the 

 hereditary transmission of the defects arising from the treat- 

 ment of the male animals. 



The same can be said for the female column, the results shown 

 here also being worse than from the normal matings. The 

 'early prenatal mortality' is higher, the average litter weight, 

 indicating the total productivity is smaller, the late prenatal 

 and total mortality are higher, while the mating failures are 

 about the same as in the control records. Therefore, the treat- 

 ment of female individuals also induces effects that are trans- 

 mitted to later generations through the germ cells. 



When, however, the records of the fourth and fifth columns 

 are compared, it is found that the treatment of male ancestors 

 gives in every point considered more marked effects on the 

 qualities of the descendants than the treatment of female an- 

 cestors. Among the descendants of treated males there is a 

 higher early and late prenatal mortality, a decidedly higher 

 total mortality, and more mating failures than among those 

 from treated female ancestors, while the first and second columns 

 show the opposite to prevail so far as litter weight and mortality 

 are concerned for first-generation, Fi, animals from directly 

 treated males and females. These inferior results, so far as 

 late prenatal and total mortality are concerned on the part of 

 the offspring from the directly treated female, may be interpreted 

 as due to the direct influence of the treatment upon the young 

 in utero. On the other hand, the improved records from the 



