Abstract
The importance of the pars anterior of the hypophysis in the control of the thyroid gland has been clearly shown in many ways and by many investigators. The writer has shown that under normal conditions of iodine content in food and water, amphibian larvae fail to metamorphose in the absence of either or both of these glands. The stage at which development ceases is the same in each instance.
It is natural to inquire which of the two glands takes the leading role in initiating the process of thyroid secretion. A crucial experiment consists in making transplants of the hypophysis taken from tadpoles of different stages of development into a uniform stage shortly before the beginning of metamorphosis. The recipients of these transplants were selected tadpoles of Bufo halophilus with a total length of 25-28 mm. and a hind limb length of 1-2 mm. At the end of from 10 to 18 days they were killed and preserved for study.
The transplants were placed in pockets under the skin median and caudal to the right eye where they could be seen during the course of the experiment. At the end of the experiment they were removed and studied in order to note their condition. Certain of these transplants were sectioned and studied histologically in order to determine their condition at the end of the experiment. Only those found suitable among the 154 tadpoles were used. These numbered 117, of which 103 received transplants and 14 served as controls.
Table I gives the results. The donor types are indicated at the left while the measure of the development induced is shown by the average hind limb length of the recipients indicated.
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