INBREEDING AND SELECTION IN DROSOPHILA AMPELOPHILA 153 
SUMMARY 
1. Drosophila ampelophila may be inbred (brothers and sis- 
ters) for seventy-five or more generations. 
2. Inbreeding in itself is not deleterious to the fertility or 
vigor of this species. 
3. ‘Infertility normally occurs to a varying degree among the 
offspring of any pair. Promiscuous inbreeding among such off- 
spring may perpetuate and even intensify this character. When 
sterility appeared in the strain experimented with, it was always 
complete, appeared suddenly and was confined to the male. 
4. By the judicious selection of the brothers and sisters 
to be mated from a brood that shows a high degree of infertility, 
this infertility can be eliminated by selection although continuing 
the inbreeding in the closest possible way. 
5. There is a wide divergence in the fertility and productive- 
ness among the different pairs taken in nature, but by the proper 
selection and closest inbreeding these may be readily brought 
to either a high or low state with respect to these characters. 
6. Many generations of closest inbreeding does not neces- 
sarily cause any loss in size, perfection of form, rate of reaction to 
light and gravity, egg production or length of life and sex-ratio. 
7. The normal sex-ratio of this species in nature when reared 
under diverse conditions of food is one male to 1.126 females. 
8. Different pairs in nature show a wide divergence in the sex- 
ratio of their offspring. 
9. When the offspring from a pair with a given ratio are mated 
in pairs their offspring will show a wide range in the sex-ratio but 
in the aggregate will tend to reproduce the ratio of the brood to 
which they belong. 
10. Sex-ratio is therefore a character that is strongly trans- 
missible. By the proper selection of pairs tending to throw a 
high female ratio on the one hand or a low female ratio on the 
other it is possible to develop strains characterized by high or 
low female ratios. 
11. In this species it is comparatively easy to develop a strain 
with a female ratio considerably higher than the normal but very 
JOURNAL OF MORPHOLOGY, VOL. 22, No. 1 
