THE RELATION OF THE THYROID AND THE HYPOPHYSIS TO THE MOLTING PROCESS IN THE LIZARD, HEMIDACTYLUS BROOKII

Abstract

Either thyroidectomy or hypophysectomy lengthened the period between molts, but neither operation entirely prevented molting. Thyroidectomy did not delay the appearance of the molt immediately following the operation but affected all later molts. If not more than 6 follicles remain after thyroidectomy, the effect is the same as complete thyroidectomy. Injections of thyroxin, 1 to 10,000 and later 1 to 30,000, given intramuscularly to thyroidectomized lizards on alternate days bring a return of the molt to its normal periodicity. However, neither injections of thyroxin nor implantations of fresh lizard thyroid increase the frequency of molt in the intact lizard. Completely hypophysectomized H. brookii turn a pale grey and remain this color permanently under varying environmental conditions. Lizards with fragments of the pars intermedia remaining turn a slightly dark tone under conditions where the controls are very dark grey. Removal of the pars anterior of the pituitary alone has the same effect on delaying the molt as removal of the whole gland. The lengthening of the interval between molts may be due to a lowering of the metabolic rate and not to any direct action of either the anterior pituitary or the thyroid on the molt mechanism.