Abstract
As is well known, the axolotl in its native habitat may retain its larval condition for long periods, even becoming sexually mature (neotonous). When treated with thyroid, when placed in unfavorable conditions or when transported to a lower and warmer region it rather promptly metamorphoses. This delicate-balance obtaining in the internal secretory glands (the thyroid and hypophysis here being of especial interest) of this form would appear to make it especially useful in the experimental modification of the activities of these glands. Since the experimental transplantation of the anuran anterior hypophysis into the hypophysectomized tadpole (Allen) and into the normal tadpole (Swingle) and the intraperitoneal injection of bovine anterior hypophyseal substance into the pituitaryless tadpole (Smith) appear to stimulate the thyroid, thus hastening or inducing metamorphosis, it would seem that the injection of this substance might be expected to accelerate metamorphosis in the axolotl. The opposite reaction, however, is evoked, the larval condition being decisively prolonged. The experimental injection of fresh bovine anterior lobe hypophyseal substance, intraperitoneally, into the Colorado axolotl during the months of May to September of the present year has resulted in a definite retardation in the metamorphosis of this form. Anterior lobe substance appears here to have given a “paradoxica:” reaction and the usual effect of thyroid activity (which most investigatorshold as immediately responsible for metamorphosis) has been greatly postponed. Pronounced darkening of the axolotl resulted from these injections of anterior lobe sulbstance, the specimen becoming after repeated injections a jet black
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