Abstract
1. Drosophila melanogaster (Oregon strain), that has long been reared by the Kozi medium (K strain), changes some characters when it is provided with the Pearl's medium (n strain). Flies, maintained on the new medium, lay more eggs per day or through their lives (averages 1.7 times) (Tables 2, 3), increase a tendency to lay eggs on the Pearl's medium (Table 5), and show an accelerated rate of development (average durations of larvae and pupae are shortened ca. 7-24 hours and ca. 5.2-9.3 hours respectively) (Tables 6, 7, 8, 9, 10).
2. When crossed, the F1 hybrids lay eggs considerably greater than the parental strains (i. e. show conspicuous heterosis) (Table 4), whereas the preference test reveals no significant difference from liking of the K strain (Table 5), and the rate of development seems to be, though slightly accelerated, nearly equal to that of the n strain.
3. We have an opinion that these changes in character are hereditary. Cautions taken in the procedures of the experiments (Fig. 1) and various results obtained seem to warrant the above opinion. As for hereditary control of these characters, both nucleus and protoplasm seem to be concerned.
