(1) The administration of active anterior lobe extracts in solution is not effective in producing precocious transformation of tadpoles.

(2) The rate of metamorphosis induced by injection of either thyroid or anterior pituitary depends within limits on the concentration of the initial dose. The time for completion with thyroid depends upon the total quantity given--a cumulative effect. The repetition of the stimulus given by a dose, the quantity per dose having maximum and minimum values, at suitable intervals decides the time of completion with anterior pituitary.

(3) Susceptibility of tadpoles to metamorphosis inducing factors increases with age.

(4) The effects produced by iodine in metamorphosis (mortality, reduction in size and shrinkage) agree more closely with those obtained in thyroid than pituitary treatment.

(5) There is a differential response of certain tissues to concentrations of the thyroid but not to anterior pituitary.

(6) Exposure of tadpoles to X-rays alters the susceptibility to factors accelerating metamorphosis. The effect increases with age.

(7) Alcohol and potassium cyanide lower the response to thyroid and anterior pituitary stimulation according to the concentration and the age of tadpoles.

(8) Normal rates of change are produced by thyroid and anterior pituitary in tadpoles under narcosis. The mortality is slightly higher with thyroid and depends on the concentration of the anaesthetic. Prolonged narcosis reduces the rate of change.

(9) Precocious metamorphosis is not found in tadpoles after feeding upon the endostyle of Ciona intestinalis.

(10) The relation to iodine, quantitative and qualitative responses of tadpoles to treatment, and the differential tissue response serve to differentiate between the metamorphic principles of the thyroid and anterior pituitary.

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