SHORTER ARTICLES AND DISCUSSIONS 



Table 142 shows the classification of extracted hooded second F, 

 .btained from crossing first F, hooded rats (table 141) with wild rats 

 looded grandparents were themselves grandchildren of $5513, +4} 

 ration 10, on the side of both parents. 



from + 2 to + 31/4. ( See table 142.) They produced several litters of 

 young of the same character as the first young, all being similar to 

 wild rats in appearance, except for the frequent occurrence of a white 

 spot on the belly. These second young were at weaning time mated, 

 brother with sister, in breeding-pens, precisely as had been done with the 

 first Fj's. They produced 394 second F, young, of which 98 were hooded 

 and 296 non-hooded, a perfect 1:3 ratio. The hooded young varied 

 in grade from +2 to +4, as shown in table 142, the data there being 

 given for each family separately as well as for all combined in the totals. 

 One family was very like another as regards the character of the hooded 

 young, except that the higher-grade grandparents had grandchildren 

 of slightly higher grade. Thus the average of all the 98 hooded young 

 was -f 3.47, but the average of those descended from the 3 grandparents 

 of lowest grade was less than this, while the average of those descended 

 from the 3 grandparents of highest grade was greater. This is just 

 what had been obser\-ed throughout the entire selection experiments. 

 (See Castle and Phillips.) 



If we weight each of the grandparents in table 142 in proportion to 

 the number of its hooded grandchildren, then the mean grade of all the 

 grandparents is + 2.95. Since the mean grade of all the 41 first F, 

 hooded grandchildren, from which these 7 were chosen, was -f 3.05, it 

 will be seen that these 7 are, so far as grade is concerned, fair repre- 

 sentatives of the 41, being in fact of slightly lower mean grade. It is 

 therefore all the more striking that their grandchildren, the second F, 

 hooded young (table 142), are of higher grade. They regress in an 

 opposite direction to that taken by the first F, hooded young. Thus 

 the original hooded ancestor (55513) was of grade 4.25. The grade of 

 hooded young expected from such animals is 3.S4. Whnt she iiroduced 



