66 CHARLES A. COBURN 



on this "singing" phenomenon in mice. In each case the 

 observations had been merely casual and the reports gave no 

 new information on the subject. 



The results of this investigation, though by no means com- 

 plete, indicate fairly definitely that this "singing" characteris- 

 tic in mice is not heritable. From the fact that no males were 

 captured that were definitely known to possess the characteris- 

 tic, and the phenomenon in two of the three individuals observed 

 was more often noted just before and after the birth of young, 

 it seems quite possible that it is a characteristic peculiar to 

 females and, perchance, due to a diseased condition or otherwise 

 structural defect of the vocal organs, caused or, at least, accen- 

 tuated by the birth of young. 



SUMMARY AND CONCLUSIONS 



1. When the grades of wildness and savageness attained by 

 mice of each hybrid generation are considered collectively, 

 the lowering of the average grades of wildness and savageness 

 in the successive tests is gradual in each generation but is great- 

 est in both wildness and savageness in the second hybrid gen- 

 eration. The greatest amount of difference in the grade of 

 wildness for any two consecutive tests occurs between the second 

 and third. 



2. The mice of Series B, as a whole, graded higher than those 

 of Series A in both wildness and savageness. This result does 

 not indicate the presence of wild blood in the tame parents of 

 the hybrids of Series A, and hence is directly opposed to the 

 results Professor Yerkes obtained with the rats. 



3. Savageness is more usually associated with wildness than 

 with tameness. 



4. The females, as a rule, attained higher grades in wildness 

 and savageness than the males. 



5. From the results of the tests of the first and second hybrid 

 generations of Series A, it was found that, generally speaking, 

 the older the mice the lesser the average grades in wildness 

 and savageness attained by them in the five tests. 



6. The decrease in the grades of wildness and savageness 

 continues with the successive tests when the number of tests 

 is increased to eight. 



7. Age, frequency of tests, number of tests, and the pres- 

 ence of the experimenter in the room, each has a certain effect 



