A. The development of the antenna buds of the mutant antennaless of D. melanogaster has been examined and it is shown that:

(1) Prior to about 70 hr., no histological difference is detectable as between normal and abnormal anlagen.

(2) Normal antenna buds continue to grow exponentially after 70 hr.; abnormal buds scarcely grow at all.

(3) The abnormal bud is also distinguished from wild type by its failure to segment.

(4) Both normal (ant. +) and antennaless (ant. -) frontal sacs are everted normally in the pupa.

B. The period during which the course of development of antennaless buds of the same genotype could be modified by specific nutritional substances was also determined. It is shown that media containing a high concentration of dextrose will induce a lowered exhibition. By transferring larvae from normal media to media of high dextrose content, it is found that the course of development of the antenna bud cannot be modified after about the 80th hr. of larval life.

These experiments suggest that the effective period of the gene is relatively short and is probably not more than 12 hr. for each individual larva. This period corresponds to the T.E.P., but is not necessarily identical with ‘the time of action of the gene’.

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