On Amphibian Metamorphosis and Internal Secretions. 5 1 



contraction, is indicative that internal secretion underlies the mechanism 



♦ 



by which the regulation of pigmental reactions is effected in normal life. 

 In any case there would appear to exist a double compensating mechauism 

 for the control of the behaviour of the melanophores : though we cannot 

 yet legitimately infer that this constitutes the effective apparatus through 

 which the organs of vision influence them. 



6. The Pineal Pigment Cycle in Tadpoles. 

 In view of the lack of success with which efforts to induce a response 

 on the part of the melanophores of the Axolotls were attended, it was 

 decided to repeat McCord and F. Allen's experiments upon pineal adminis- 

 tration to Anuran tadpoles. About 500 tadpoles of Eana temporaria were 

 employed for this purpose in glass containers during the spring of 1921. 

 At first the controls (meat-fed), and the experimental animals which were 

 fed on fresh ox pineal glands tri- weekly, were kept respectively in single 

 containers. Later, for purposes of observation, the tadpoles were separated 

 in glass bowls (placed on a white background) in colonies of twenty. 

 Contemporaneously, tadpoles raised from eggs laid on the same day were being 

 fed on suprarenal cortex, suprarenal medulla, corpus luteum, and anterior 

 pituitary lobe for ulterior purposes, so that it was possible to compare the 

 phenomena consequent upon pineal treatment with the results of adminis- 

 tration of a more varied range of tissue extracts than were employed by 

 the authors named above. 



In these experiments no change in the pigmental characteristics of the 

 tadpoles was noticed during the first fortnight of pineal diet, which began 

 about a fortnight after hatching. Before three weeks had elapsed, the 

 phenomena of the pineal pigment cycle, as recorded by its discoverers, 

 became evident. Within a quarter of an hour of feeding the tadpoles 

 became visibly more pale, till, when the reaction reached its maximum, 

 half an hour after the meal commenced, they assumed a quite unique 

 appearance, by virtue of the contrast between the complete translucence 

 of the head region and tail on the one hand, and the opacity of the 

 visceral portion of the body on the other. This condition passes off after 

 the lapse of five or six hours : till metamorphosis took place the same 

 reaction followed each administration with the utmost regularity. No 

 modification of the pigmental features occurred in the controls or in the 

 additional cultures which were being fed synchronously with other glandular 

 tissues. Histological preparations confirmed McCord and Allen's conclusion 

 that the behaviour of the melanophores is the significant element in the 

 situation. After a pineal meal the melanophores are fully contracted, 



E 2 



