INBREEDING AND SELECTION IN DROSOPHILA AMPELOPHILA 129 
of brothers and sisters from the same parents, however, were fer- 
tile. Judging from the productiveness of these, there was often 
a wide divergence. It would seem that, as a result of inbreeding, 
we had a condition of fertility ranging from absolute infertility 
to comparatively high fertility among the different pairs of brothers 
and sisters from any given pair of parents. To test this the follow- 
ing experiment was carried out: About two-hundred eggs from 
each of fifteen pairs of flies were laid out after the fashion indicated 
above. Ten of these pairs had been inbred for seventeen genera- 
tions while five belonged to fresh stock that had not been inbred. 
Of the ten pairs of the inbred strain, five belonged to a strain 
which had arrived at a very low degree of fertility, namely only 
36 per cent of the forty-two pairs tested were fertile (table 3, 
seventeenth generation, strain, A). These five pairs were brothers 
and sisters to many of the sterile pairs considered in the preceding 
section. 
The other five pairs (of the ten inbred) were from a strain which 
had been held by selection to a high degree of fertility, namely 
97 per cent of the thirty-four pairs tested were fertile. Both of 
these strains were descended from common great grandparents 
(table 3, seventeenth generation, strain B). | 
We have, thus, for comparison three conditions, namely, (1) 
eggs from a highly infertile inbred strain; (2) eggs from a highly 
fertile inbred strain; and (38) eggs from a presumably norma 
strain that had not been inbred. It should be added that the 
five pairs were taken at random and were not selected. Approxi- 
mately the first two-hundred eggs of each pair were laid out in 
batches of about twenty to twenty-five to the vial. The number 
of eggs that hatched was noted in each case and also the number 
that emerged as imagos. Table 1 gives the summary of results. 
From this table it appears that from the eggs which were taken 
from the inbred pairs with low fertility practically as large a per 
cent (97.27) hatched as from the eggs that came from the inbred 
pairs that showed a high fertility (98.2). The same is true in 
regard to the number that produced imagoes, 86.8 per cent and 
85.1 per cent respectively. The fact clearly brought out here is 
that when infertility arises in this strain it arises suddenly and 
JOURNAL OF MORPHOLOGY, VOL. 22, No. 1. 
