ss 



Heredity and Eugenics 



was now directed toward two ends: (i) to secure animals 

 which were free from spots of red or white, a condition 

 which was present in the original stock; and (2) to secure 

 extensi\x' and uniform sihx'ring on a black background. 

 In both these objects good progress has been made. We 

 ha\'e animals which are sih-ered all over the body except 

 on a jxvrt of the head, and the percentage of such well- 

 sih'ered indi\'iduals is relatively high. 



A more extensive selection ex]3eriment is one in which 

 I have been assisted by Dr. John C. Phillips (Figs. 31 and 3 2). 



Fiij. 31. — DiuKram showing variation in tlie color pattern of hooded rats. 

 Numerals indicate arbitrary grades used. 



Selection in this case has been directed toward a modifica- 

 tion of the color pattern of hooded rats, a pattern which is 

 known to behave as a recessive Mendelian character in 

 crosses with either the self (totally pigmented) condition 

 or the so-called Irish (^vhite bellied) condition found in 

 some other rats. The extreme range of variation among 

 our hooded rats at the outset of this experiment is indicated 

 bv the grades —2 and +3 of Fig. 31. Selection was now 

 made of the extreme variates in either direction and these 

 were bred sei)arately. Two series of animals were thus 



