FACTORS INFLUENCING GROWTH AND METAMORPHOSIS OF THE SALIVARY GLAND IN DROSOPHILA

Abstract

1. The normal development of the salivary gland of Drosophila virilis is described. Eleven successive stages of development have been distinguished.2. Larval salivary glands of different ages were transplanted into the abdomens of older larvae and thus exposed prematurely to the metamorphosis factor. It was found that the metamorphosis of the transplanted glands is not autonomous but depends upon some factor in the host.3. Glands as young as stage 3 are unable to react to the metamorphosis factor and persist as larval tissue in the adult fly. However, glands transplanted at stage 5 metamorphose synchronously with the host and hence undergo a premature metamorphosis. In these cases the transplanted larval glands are completely histolysed, and the simultaneously transplanted anlagen of the imaginal salivary gland differentiate into adult salivary glands.4. Salivary glands of older larval donors transplanted into younger hosts metamorphose before the host glands show any signs of metamorphosis.5. Larval salivary glands of various ages were transplanted into the body cavity of adult male flies. The thus transplanted glands ceased to grow and remained unchanged even when left for a considerable length of time in their adult environment. If, however, ring glands of old larvae are transplanted together with salivary glands into the adult host, the growth of the salivary glands is restored, leading finally to metamorphosis. These facts have been demonstrated very clearly by using salivary glands of a single donor and transplanting one partner into one host without ring glands and the other partner into a second host together with ring glands.6. The number of ring glands implanted is of no great importance for the development of the salivary glands, since two ring glands have about the same effect as four ring glands. However, one ring gland is presumably somewhat less effective than four ring glands.7. The rate of metamorphosis of the salivary gland in adult hosts is decidedly slower than in normal development.8. Younger salivary glands metamorphose later than older salivary glands under the influence of the same number of ring glands.9. Although the young glands metamorphose later, their metamorphosis is premature as far as their state of development is concerned.10. A comparison of the time of metamorphosis of salivary glands in adult and larval hosts shows that metamorphosis proceeds much more rapidly in larval hosts in spite of the fact that in the adult host the salivary glands may be under the influence of as many as four ring glands.11. The ring gland factor is presumably hormonal in nature, and is not species-specific.12. The role of hormone concentration and tissue competence in the determination of the various stages of growth and differentiation in the development of the salivary glands is discussed.