106 



TRE AMERICAN NATURALIST 



[Vol. LI 



Each of these animals was mated with a single wild mate, and their 

 children were weaned directly into breeding cages containing a male 

 and two or three females (brother and sisters). In the case of two 

 matings, males of the same parentage were at the time lacking and 

 males from a different cross were used. The results of such matings are 

 tabulated by themselves and serve a useful purpose as controls. The F, 

 animals all closely resembled their wild parents, but many of them had 

 a white spot on the chest. They ranged from grade +5iA to +6 

 (self). 



The F, animals are classified in table 141, where it appears that 73 

 of them were hooded and 219 non-hooded {i. e., like FJ, an exact 1:3 

 ratio. More than half of this F, generation consists of the grand- 



children of $5513, produced by breeding her children brother with 



grandchildren include 41 hooded and 107 non-hooded young. The 

 hooded young range in grade from -+- iy2 to + 4, their mean grade be- 

 ing + 3.05, a considerable regression from the grade of the grand- 

 mother, which was 4.25. 



Hooded rats of the same grade and generation as the grandmother, 

 when bred with each other, produced young of mean grade 4-3.84. 

 (See table 10. Castle and Phillips.^) The mean of the extracted 

 hooded grandchildren in this case (being 3.05) shows a regression of 

 0.79 from that expected for the uncrossed hooded race. From the 

 extracted hooded grandchildren of $5513, produced as just described 

 by a cross with a Avild male, 7 individuals, 2 males and 5 females, were 

 selected for a second cross with the wild race. They ranged in grade 



2 Comparison should have been made with generation 11 offspring, whose 

 mean was 3.91 not 3.84. This would make the regression 0.86, instead 



