HORMONES AND TISSUE COMPETENCE IN THE DEVELOPMENT OF DROSOPHILA

¹ Department of Zoology, Columbia University, New York

A variety of organ discs of Drosophila was transplanted together with or without ring glands into the body cavity of adult flies and their developmental behavior in their new surroundings studied. The specific results of these investigations are briefly summarized as follows:

1. Organ discs transplanted into adult male hosts cease to develop but remain alive presumably indefinitely. The transplanted discs do not lose their developmental potencies, although development may be arrested for a long time.

2. Organ discs transplanted into adult male hosts will grow and finally differentiate to imaginal completion when under the influence of simultaneously transplanted ring glands.

3. Organ discs transplanted into adult female hosts continue their development at a very slow rate even in the absence of ring glands.

4. There is no difference in the organic environment of different species as far as the development of test organs is concerned. If however, different host species are provided with the same number of ring glands it is found that the ring glands have a greater effect on the development of the test organs in melanogaster than in virilis hosts.

5. Ring glands of all larval ages, even from larvae only 12 hours old, are able to induce growth in the transplanted test organ.

6. The amount of hormone produced by young larval ring glands is less than that produced during the same time interval by ring glands of mature larvae.

7. Different organ discs differ as to their capacity to differentiate in adult hosts under the influence of ring glands.

8. Different regions within the same organ disc also differ as to their differentiation capacity.

9. Under the same hormonal environment it takes the young organ discs a considerably longer time to complete differentiation than it takes the old organ discs.

10. The ring gland hormone, apparently, does not affect the reacting organ directly, but acts rather through the intervention of some as yet unknown factors in the host.

11. The kind of organ response, that is, whether the organ disc responds with growth or differentiation to the ring gland hormone depends upon the relationship between hormone concentration and organ responsiveness.

12. The problem of growth and differentiation in the development of Drosophila is discussed. It is pointed out that development is not the reflection of absolute conditions but that it is highly relative indeed; it is the expression of a very delicate balance between the activating and reacting systems involved.