52 



Messrs. J. S. Huxley and L. T. Hogben. 



the pigment being congregated into compact masses in the centre of the 

 cell. * 



The time relations observed are somewhat different in these experiments 

 from those obtained by McCord and Allen. Thus the latent period was a 

 little longer ; the time required for the effect to manifest itself after feeding 

 a little shorter, and the duration of the effect considerably longer. In the 

 case of E. sylvatica, these investigators found that the reaction passes off 

 in about two hours. Apart from these insignificant details, the experiment 

 recorded entirely confirms their results. It may be added that extracts were 

 also employed and produced rapidly (less) corresponding effects to those 

 produced by administration per os. 



As regards the cortex-fed cultures, no difference was seen in the pigmenta- 

 tion of tadpoles fed continuously from hatching till metamorphosis on supra- 

 renal cortex as contrasted with controls. We take the opportunity of 

 putting this observation on record, because Gudernatsch (1914) stated that 

 cortex-fed tadpoles show progressively less pigment after five weeks' treat- 

 ment, an observation which, if confirmed, would seem significant in relatiou 

 to the aetiology of Addison's disease. 



That the pineal gland of Amphibia does actually function in relation to 

 pigmental responses, although it is probable, cannot be legitimately contended 

 on the basis of evidence so far available, as mammalian pineal glands were 

 employed in the experiments. What can be definitely stated is that pineal 

 tissue is specifically distinguished by the possession of a physiologically active 

 substance, a conclusion which goes far to establish its claim to be classified 

 as an endocrine organ. 



Summary. 



A. Metamorphosis. 



1. Salamandra and Triton larvae may be metamorphosed by immersion in a 

 dilute solution of iodine. Metamorphosis is retarded by low temperature. 

 High temperature at first causes increased growth of the gills. 



2. Sexually mature Axolotls can, as Laufberger and Jensen originally 

 showed, be made to undergo metamorphosis by means of a thyroid diet. 



3. Metamorphosis is accompanied by exophthalmos, apparently in all 

 Amphibia. 



4. In the case of the Axolotl, the time required for metamorphosis 

 induced by enforced air-breathing is considerably longer than when induced 

 by thyroid-feeding ; in the latter case, it is longer for sexually mature 

 than for young larva? ; and is in all cases accelerated by increase of 

 temperature. 



5. Administration of iodine free of organic combination, or fresh glandular 



