ABSTRACT
The ultimobranchial body originates independently of the thyroid, as seen in congenitally athyreotic tadpoles of P. syriacus.
Experiments concerning the influence of the hypophysis and thyroid on the ultimobranchial body were performed on H. arborea, R. ridibunda, and B. viridis.
With the beginning of metamorphosis, the increasing thyroid secretion inhibits the original growth rate of the ultimobranchial body; experimental hyperthyroidism enhances this physiological interference, so that the follicle shrinks.
Experimental hypothyroidism causes hypertrophy of the ultimobranchial body, evidenced by an increase in surface area of the follicle. This effect is negligible before metamorphosis, significant during metamorphosis, and less extreme in young adults, when thyroid activity declines.
Hypophysectomy in young adults causes atrophy of the organ.
It is assumed that the hypophysis maintains the ultimobranchial body and the thyroid inhibits its growth and activity. The antagonistic effects of both glands produce the normal state of the organ.
