THE EFFECTS OF TEMPERATURE GRADIENTS ON THE PUPAL-ADULT TRANSFORMATION OF SILKWORMS

¹ Society of Fellows, Harvard University

1. Diapausing pupae of the silkworms, Samia walkeri (cynthia) (F.& F.) and Telea polyphemus (Cram.), were placed in a diaphragm and one end exposed to a temperature of 25° to 30° C. and the other end to a temperature of 3° to 5° C. There was thus established a longitudinal temperature gradient in each individual.

2. Development took place in the majority of animals thus treated. For each of these pupae evidence was found that the termination of diapause occurred simultaneously throughout the animal. This observation suggests the existence of a developmental center which evokes the overall initiation of adult differentiation.

3. An analysis of the results obtained when the head and thorax were heated with those obtained when this region was chilled permits a rough localization of such a developmental center in the anterior end of the pupa. Since a similar relationship has been noted for non-diapausing pupae by previous investigators, it is possible that diapausing and non-diapausing developments differ primarily in regard to the time at which the developmental center attains an activity sufficient to stimulate adult differentiation.

4. After the pupal-adult transformation has once been initiated, the tissues are capable of a high degree of developmental autonomy. Animals were produced which were wholly mature at the heated end while the cold end remained in an earlier stage of adult formation. This result was also observed within single organs. In such cases the developmental velocity of each region was related to the local metabolic conditions as affected by the temperature gradients.

5. Of particular interest were the effects of temperature gradients upon moulting and pigmentation, processes that are generally recognized as involving the action of chemicals of a hormonal nature The contrasting results observed in the hot and cold regions, notwith standing their uniform blood supply, emphasizes the importance of issue competency in carrying out hormonal reactions.