PHYSIOLOGY OF INSECT DIAPAUSE. III. THE PROTHORACIC GLANDS IN THE CECROPIA SILKWORM, WITH SPECIAL REFERENCE TO THEIR SIGNIFICANCE IN EMBRYONIC AND POSTEMBRYONIC DEVELOPMENT

¹ The Biological Laboratories, Harvard University, Cambridge, Massachusetts

1. The data relative to the thoracic control of insect development are suryeyed. Embryonic development seems to be controlled by a thoracic center in all insects. Postembryonic development seems to be controlled by a thoracic center in at least the Lepidoptera and the Megaloptera.

2. In the Lepidoptera the thoracic center for postembryonic development can be identified as the "prothoracic gland." A review is presented of the literature describing these organs.

3. The thoracic center for embryonic development coincides with the position occupied by the prothoracic glands in lepidopterous embryos. It is therefore possible that the prothoracic glands may function as the embryonic differentiation center in at least certain species.

4. The morphology and histology of the prothoracic glands are described in the Cecropia silkworm. Homologous organs are present in saw-fly larvae and most probably in the walking-stick, Dixippus.

5. Since prothoracic glands, or their homologues, may be widely distributed in embryonic and postembryonic stages of insects, these organs present special physiological interest and merit further study.