Abstract
In an effort to find a common ground between developmental and population genetics, techniques have beep developed for observing and measuring some embryonic characters in D. melanogaster. Measurements made on developmental rates in 3 strains show strain differences, but these differences are not simply expressible as constants. Instead, relative rates differ at different stages of development, and strain has a characteristic pattern of development. These patterns appear to indicate the different ways in which different genetic systems produce the arrays of adult phenotypes which characterize different populations. They must be observable expressions of different biochemical events.