Effect of Multiple Pituitary Primordia in the Tadpole. ∗

Abstract

That the pituitary plays a prominent part in controlling metamorphosis and sexual maturity in vertebrate development is clearly established. But little is known of the factors that determine pituitary activity at these times. This study is directed at the analysis of these factors in the metamorphosis of the tadpole.

The experimental animals drawn from the same batch of Rana sylvatica eggs were prepared as follows: (1) 30 normal unoperated controls; (2) 116 in which the buccal primordium of the hypophysis was removed in the tail bud stage; (3) 48 hypophysectomized, but with the hypophyseal primordium reimplanted either into the eye cup or under the adhesive discs; (4) 50 as in No. 3, but with the addition of 3 primordia implanted under the adhesive discs. The superficial ectoderm was generally included with a minimum of brain tissue, but no attempt was made to remove all possible adherent brain. When the animals were sufficiently developed to determine the success of the grafts in terms of the pigmentation reaction they were made up into sets consisting of one “successful” animal of each type. Of 10 sets 6 were carried through metamorphosis successfully. The animals were kept at 26-29°C.

Group 4 with 4 pituitary transplants metamorphosed precociously as compared to groups 1 and 3. The time required to accomplish a definite metamorphic change, the resorption of the anal canal piece, in group 4 averaged 7.8 ± 1.4 days after the experiment was set up. For groups 1 and 3 these figures were 17.7 ± 0.6 and 19.8 ± 1.7 days respectively. A more significant measure of precocity is the maximal size attained by the tadpoles previous to the reductions incident to metamorphosis. This averaged 28.7 ± 1.5 mm. for group 4 and 43.5 ± 0.6 mm. and 45.2 ± 1.0 mm. for groups 1 and 3. The group 4 animals were not only smaller than their controls at metamorphosis but in 5 of the 6 cases entirely below the range of variation of normal animals as seen in the author's experience with this species. The animals with single grafts were not accelerated.