The Corpus Allatum and Moulting in Bhodnius.
1. The stretching of the cuticle which initiates moulting is necessary only as a stimulus for the secretion of the moulting hormone. The hormone so produced will induce moulting in unfed nymphs.
2. The simultaneous moulting of joined insects is dependent on the continuity of the epidermis established between them. But moulting can be induced by the medium of the blood without contact between the tissues.
3. The moulting hormone from Rhodnius will induce moulting in bugs of the allied genus Triatoma and in the bed-bug, Cimex. The epidermis of these joined insects grows together during the process.
4. Some rather indirect experimental evidence that the corpus allatum secretes the moulting hormone is given.
5. The corpus allatum secretes the ‘inhibitory hormone’ which prevents metamorphosis in the earlier nymphal stages. Fifth-stage nymphs with the corpus allatum of 3rd- or 4th-stage nymphs implanted in them give rise to ‘6th-stage’ nymphs. These ‘6th-stage’ nymphs may give rise to ‘7th-stage’ nymphs when they moult again.
In some transplantation experiments the characters all over the body may be intermediate between nymph and adult; or nymphal characters may only be developed near the implant.
6. The inhibitory effect is non-specific as between Rhodnius, Triatoma, and Cimex.
7. The corpus allatum also determines the characters of each nymphal instar by limiting the degree of differentiation towards the adult form which occurs during the moult.
8. In the phenomenon of ‘inhibition of metamorphosis’ there seem to be two elements: (i) deposition of the new cuticle follows rapidly upon the initiation of growth and hence differentiation of the adult characters is arrested; (ii) so long as differentiation is arrested in this way the cells are capable of renewed growth and will respond again to the ‘moulting hormone’.
9. Whether the ‘moulting hormone’ is chemically distinct from the ‘inhibitory hormone’ is not proved.
The Corpus Allatum and Reproduction in Rhodnius.
1. In the adult female the corpus allatum is necessary for the production of ripe eggs. The secretion from the corpus allatum of Triatoma females will cause egg development in Rhodnius.
2. In the absence of this secretion the oocytes continue to grow so long as they are connected to the nurse cells. They die and are absorbed when their nutrition is taken over by the follicular cells.
3. The moulting hormone of the nymphal stages will not cause egg development in the adult female; nor will the egg-forming hormone induce moulting.
4. The corpus allatum in the adult male is necessary for the normal activity of the accessory glands. Its secretion will induce egg development in the adult female; and the secretion from the female will activate the accessory glands of the male.
