PHYSIOLOGY OF INSECT DIAPAUSE. II. INTERACTION BETWEEN THE PUPAL BRAIN AND PROTHORACIC GLANDS IN THE METAMORPHOSIS OF THE GIANT SILKWORM, PLATYSAMIA CECROPIA
Abstract
1. The mechanism that initiates adult development after pupal diapause has been studied in a total of 282 experiments, supplementary to those reported previously.
2. Brainless, diapausing pupae were divided transversely and the developmental capacities of anterior and posterior fragments tested and compared.
3. Implantation of a previously chilled brain sufficed to terminate the dormancy of anterior fragments.
4. Isolated abdomens, to the contrary, remained undeveloped after brain implantation. Yet such abdomens, even without implantation, could be induced to develop by grafting them to developing anterior fragments. Manifestly, the abdomens required for development an additional factor normally produced in the anterior end of the pupa.
5. By transections at various levels the source of this additional factor was found to be the thorax.
6. A testing of various thoracic organs revealed the effectiveness of the "prothoracic glands." Thus, implantation of a chilled brain plus prothoracic glands induced the complete adult development of isolated abdomens. In this effect the prothoracic glands as well as the brain showed a lack of species—or genus— specificity.
7. The termination of diapause requires in these species the action of a minimum of two factors, one arising from the brain and the other from the prothoracic glands. The brain factor is necessary for the activation of the prothoracic glands.
8. The factor from the prothoracic glands, most probably, has ultimate action on the tissues in terminating diapause.
9. The brain is the organ of primary control over diapause in the species studied, but this control, at least in part, is exercised by an indirect mechanism.
