28o 



BIOLOGY OF THE LABORATORY MOUSE 



The subsequent occurrence of a susceptible animal among mixed hybrids of 

 F2 and more advanced generations reopened the question, however, and 

 suggested the need of further study (86). 



Table i 



Growth or an Adenocarcinoma or the Mammary Gland (JwA) of Japanese 



Waltzing Mice, in Japanese Waltzing Mice, Common Mice and 



Their Fi, F2 and F3 Hybrids 



In 19 16 Little and Tyzzer (51) reported on a larger series of mice inocu- 

 lated with tumor JwA. A total of 629 mice were used. The results in the 

 more important generations are summarized in Table 2. 



Table 2 

 Growth of Tumor JwA in Japanese Waltzing Mice, in Common Mice 

 and in Various Hybrids between These Two 



The incidence of susceptible animals in F2 required further analysis and 

 if possible a genetic explanation. 



In 1 9 14 Little (44) had published a brief note on a type of inheritance 

 which might occur and which would give the appearance of being non- 

 Mendelian, although actually depending upon Mendelizing genes. It was 

 the continuation and development of simpler experiments already recorded 



