Developmental capacities of young and mature, wild-type andopht eye imaginal discs inDrosophila melanog aster.

1. The wild-type mature eye disc, when implanted into a larva of the same age, undergoes metamorphosis along with the host, and produces exactly one half of the head capsule outside the frontal suture. Implants ofopht eye discs form fewer facets, but many additional vibrissae, and produce homoeotic wing tissue (Fig. 1) in 20% of the cases. 2. On the basis of results with fragmented discs an organ map of the wild-type eye disc was constructed (Fig. 3), showing the presumptive eye area to be located in the flat part of the disc, surrounded by the primordia of the hypodermal head structures in the peripheral folds of the disc. 3. Probably the whole presumptive eye area inopht discs is capable of wing formation; the protuberances later giving rise to wing outgrowths are localized in this eye area. The presumptive wing area was more closely determined by separate transplantation of protuberances. The anlagen of the supernumerary vibrissae inopht discs are located in the anterior border of the disc (Fig. 4). 4. Very young head segments were cultured in adult, wild-type hosts for some weeks, and transplanted back into full-grown wild-type larvae. They terminated larval development in the adult hosts, and beside the derivatives of the eye disc produced additional wing tissue, that was shown to be homoeotic (Fig. 5). It was concluded that the homoeotic wing tissue is not induced in the disc by the mutant larval environment, but develops autonomously.