EXPERIMENTAL EVOLUTION. 



137 



"During the summer of 1920, Mr. L. C. Strong conducted experiments on 

 the reaction of wild mice to implants of these two tumors. Each mouse was 

 inoculated on the same day with dBrA on the right side and with dBrB on the 

 left. The mice have been observed at weekly intervals, beginning at a date 

 two weeks after inoculation. Those showing a palpable mass are designated 

 + ; those negative, — ." 



Table 14. — Comparison of reaction of mice to tumors in dBrA and dBrB. 



The difference between the percentages of observations showing in- 

 dications in the two tumors is 8.75 ±1.51 or 5.7 times its probable error. 

 This demonstiates that even in the small number of observations re- 

 corded we have in the reaction to implants of the tumors a phj'siologi- 

 cal test more delicate in its discrimination than is the histological test, 

 which failed to show notable differences between the two tumors. The 

 experiment indicates that reaction to tissue implants may be used 

 as a comparative method which gives an extremely delicate test of 

 physiological differences. Mr. Strong is also studying the effects of 

 gonadectomy and splenectomy on growth of implants of these tumors 

 and will continue the work during the ensuing year. 



HEREDITY OF MENTAL AND PHYSICAL TRAITS IN DOGS. 



A study has been undertaken on the method of inheritance of in- 

 stincts and other traits in dogs. This work is under the immediate 

 charge of Dr. E. C. MacDowell. On September 1, 1920, the laboratory 

 possessed 7 male and 6 female adult Dachshunds and 14 pups. Four 

 litters have been born, with the loss of only one animal, which died at 

 birth. There were also 1 male and 3 young female English setters. 

 All of the breeding animals are of standard-bred stock. Already much 

 work has been done in testing instincts of the individual breeding 

 animals, and some special methods of measuring strength of instincts 

 have been worked out. 



HEREDITY IN SHEEP, RABBITS, AND POULTRY. 



The experiments on heredity of twinning and multinipples in sheep 

 were continued. A new and young ram, born 1919, himself one of 

 triplets, was used as a sire for the lambs born in 1920. There were 28 

 lambs born from 21 mothers, being a proportion of 1.3 lambs per 



