378 HELEN DEAN KING 



9. The constitutional vigor of these rats was apparently not im- 

 paired to any extent by inbreeding. Only two kinds of malfor- 

 mations were found in the animals of the inbred strain after food 

 conditions were improved: one individual was born tailless and 

 about a dozen individuals lacked one or both eyeballs. Both of 

 these defects occur in outbred stock Albinos and neither appears 

 to be heritable. 



10. Under the conditions of these experiments the span of life 

 in both the males and females in each of the inbred series was in- 

 creased. The records show that inbred males tended to live 

 longer than did inbred females : a reversed relation was found in 

 the animals of the control series. In the inbred colony as a whole, 

 the females seemed to be longer lived than the males and they 

 were less susceptible to disease at all ages. 



11. According to the behavior tests that were made, inbred 

 Albinos are slower, less active, more timid and nervous, and some- 

 what more savage than stock Albinos that are outbred. 



12. High fecundity, early sexual maturity, and vigorous growth 

 are characters that seemed to be inherited as a group in the inbred 

 strain of rats. It seems probable that the genetic factors on which 

 these characters depend do not segregate independently, but 

 tend to combine in gametogenesis. 



13. The animals of the A series were slightly more fertile than 

 the animals of the B series, they attained sexual maturity earlier, 

 as a rule, and they lived longer. These differences probably 

 depended in some way on a dissimilarity in the gametic consti- 

 tution of the two pairs of individuals with which the experiments 

 were started. 



14. The results obtained in these experiments do not accord 

 with the general view regarding the effects of inbreeding, since 

 they indicate that inbreeding per se is not necessarily inimical 

 either to fertility or to vigor. Success or failure in any series 

 of inbreeding experiments would seem to depend on the character 

 of the stock that is inbred, on the manner in which breeding 

 animals are selected, and on the environmental conditions under 

 which the animals are reared. 



