MULTIPLE FACTORS 253 
was tried. The P, of the reversed minus line be- 
longed to the 7 (and ‘‘71”’) generation of the minus 
selection series. This generation had shown an 
average grade of —1.56, which represented a re- 
gression of 0.30 from those extreme individuals 
(—1.86) of generation 6 from which they had arisen. 
The range of generation 7 was from 0 to —2.50. 
Some of the low-grade offspring ranging from 
—0.37 to —0.87 were chosen for the return selection. 
They produced 118 offspring whose average was 
—1.28, a regression of 0.68, which is in the opposite 
direction from the regression obtained in the 
former (minus) selection. For six generations the 
reversed selection went on and carried the race back 
along its former course, 7.e., toward its original 
condition. The fact that selection in the original 
direction was still producing some effect when the 
reversed selection began, means, on the multiple 
factor hypothesis, that the stock was still heter- 
ogeneous, in some factors at least, and, therefore, 
reversing the process would be expected to give 
the results that Castle and Phillips obtained. 
These important results of Castle and Phillips 
fulfil so entirely the expectation for multiple factors 
that they might have been utilized as a good illus- 
tration of the effects of selection on a group in which 
a particular character owed its modifications to 
multiple factors. The results are, however, of addi- 
tional historical interest because they were used 
for several years as the favorite experimental ‘‘ dem- 
onstration” for a very different conception. The 
