No. 600] PIEBALD RATS AND MULTIPLE FACTORS 731 



the generations from which the parents came have been 

 used for comparison in eight of eleven crosses, it ap- 

 pears to be a more fair procedure to compare the aver- 

 ages of the offspring produced by parents of the same 

 grades and generations as used in the crosses. Suppose 

 the hooded parent crossed was grade 2, from the fourth 

 generation, then the average of the of spring from par- 

 ents of grade 2 from generation 4 should be compared 

 with the hooded offspring in F 2 . In other words, the 

 average to be used for comparison would be found in 

 generation 5. On this basis the comparisons shown in 

 Table I have been made. Returning now to the state- 

 ment at the head of this section, that when crossed with 

 wild, the earlier generations of the plus race are only 

 slightly reduced in pigmentation, this table shows that, 

 when third generation parents were crossed, the extracted 

 hoodeds were lowered .04; when fifth and sixth genera- 

 tion parents were crossed, the lowering of their hooded 

 grandchildren was greater, .17; when the hooded parent 

 came from the tenth generation, the average of the hooded 

 grandchildren was lowered .76. 



the Effects of Crossing on the Averages and Standard Devia- 

 tions of the Extracted Hoodeds 

 Numbers in brackets are those given by Castle and Phillips. 

 A. Comparisons of the Averages of Extracted Hooded Bats with the Aver- 

 ages of the Offspring of Hooded Bats of the Same Grade and Genera- 

 tion as the Hooded Bats Used as Parents in the Various Crosses. 



Generation from which hooded parent came 2% 6 10 



Average grade of F 2 hoodeds + .31 + .25 + .'25 



Average grade of uncrossed hoodeds — 1.18 — 1.72 — 2.12 



Average grade of uncrossed hoodeds as 



published (— 1-20) (—1.59) (—2.05) 



Raised by cross 1-49 1.97 2.37 



Generation from which hooded parent came 3 5 + 6 10 



Average grade of F 2 hoodeds + 2.56 + 2.97 + 3.15 



Average grade of uncrossed hoodeds + 2.60 + 3.14 + 3.91 



Average grade of uncrossed hoodeds as 



published (+ 2.60) (+ 3.14) (+ 3.84) 



Lowered by cross 04 .17 .76 



