INBREEDING AND SELECTION IN DROSOPHILA AMPELOPHILA 143 
nature, the one showing a high, the other a low female ratio. 
These were selected as the parents of the twostrains to be developed. 
From among the offspring of each of these two pairs a number of 
single matings were made. From among these the pair that 
showed the most favorable ratio in the desired direction was 
selected to continue the strain. The same process was repeated 
as often as desired. 
From a number of pairs taken from a banana bunch in Bloom- 
ington June 12, 1907, two such pairs were obtained. These two 
pairs go by the numbers 206 and 207, showing the following ratio: 
206—52 7:135 ¢ or 1:2.59 
207—84 7:75 2 or 1:0.89 
A. Strain 206 (high female ratio). The 206 strain will, for 
convenience, be called the female strain and the 207 strain the 
male strain, although, as will appear, the latter never developed 
into a predominantly male strain. In tables 8 and 9 are given in 
diagramatic form the results of selection for five generations in the 
former and six generations in the latter. At the margin the genera- 
tions are numbered 1, 2, 3 etc., and the sex-ratios are indicated. 
The sex-ratio of the eleven pairs of brothers and sisters mated 
from the first generation of the female strain (206) varied from 1:93 
Gove mee) tol: 7200 (S 3: 56 2). 
The unusually high female ratio in the latter is probably attri- 
butable to the small number of individuals obtained from this 
pair. Two of the pairs threw a predominance of males (table 
8 nos. 4 and 8). With the exception of no. 5, all the remaining 
pairs threw a high female ratio. The ratio for all the pairs was 
1:1.67 (578 7: 969 ¢). Wehave here a female ratio very much 
higher than that characteristic of the species (1:1.14) and yet 
considerably below that of the parent pair (1:2.59). This may be 
regarded as a regression toward the normal ratio. It should be 
pointed out here that too much emphasis should not be placed 
upon the exact figures representing the ratios in the different pairs, 
since the number of individuals at best are rather small. In most 
cases, however, when the number of offspring obtained is fairly 
large, the ratio approximates the true one, so that in any given 
