HOODED CROSSED WITH WILD. 167 



rats, the hooded character in this case being derived from 9G955, 

 grade +4, generation 12. The character of her first F 2 descendants is 

 shown in table 141. They consist of 5 hooded and 27 non-hooded 

 individuals. The mean grade of the hooded young is 3.51, but the 

 number of these young is too small to make this mean of much signifi- 

 cance. One of the hooded young (d"9660,+3f) was mated with a wild 

 female to secure a second F : generation and from this in due course was 

 produced the second F 2 generation (table 144) . It consisted of 21 hooded 

 and 44 non-hooded young. The hooded young showed the usual range 

 (2 to 4). Their mean grade was 3.50, substantially identical with that 

 of the first F 2 animals, but 0.25 below that of the actual hooded grand- 

 parent. This family history is less satisfactory than the two already 

 discussed because of the smaller numbers which it includes. It con- 

 tains nothing contradictory to the interpretation already given, though 

 reversed regression is not in this case in evidence. 



In two cases Fi females could not be mated with brothers and so 

 mates were taken from other families. Thus "mixed Fi matings" 

 were made between children of 5513 and 6600 and children of 5513 and 

 6955. (See table 141.) The former mating produced 3 hooded and 

 12 non-hooded " first" F 2 young; the latter produced 2 hooded and 5 

 non-hooded " first" F 2 young. The grade of the hooded young pro- 

 duced by these mixed matings was not different from that of brother- 

 sister matings, so far as the small numbers permit one to judge. One 

 of these mixed matings was carried into a second F 2 generation. The 

 first F 2 hooded ^9711, +3|, was mated with a wild female, and the 

 young were bred, brother with sister, producing 16 hooded and 33 non- 

 hooded young. (See table 144.) The mean grade of the 16 hooded 

 young was 3.28, nearly the same as that of the first F 2 hooded grand- 

 parent. No additional regression through loss of modifiers (or other 

 agency) is here in evidence. The result is the same as that observed 

 in families wholly unmixed. The attention of my pure-line critics, 

 who think that in our mass-selection experiments insufficient attention 

 has been given to individual pedigrees, is particularly directed to the 

 foregoing case. 



Having now discussed each family history separately, we may com- 

 bine all the second F 2 families in one table, in order to get a clearer 

 impression of the results as a whole. (See table 145.) The second F 2 

 generation thus combined includes 256 hooded and 749 non-hooded 

 individuals, a ratio of 1 : 2.9, an unmistakable mono-hybrid Mendelian 

 ratio. The mean grade of the hooded individuals is 3.34. The 

 weighted mean grade of their hooded grandparents was 3.02, which 

 indicates a reversed regression of 0.32 for the entire second F 2 group of 

 hooded animals. 



Classified according to the grade of the (first F 2 ) grandparent, they 

 show a correlation between grade of grandparent and grade of grand- 



