On Amphibian Metamorphosis and Internal Secretions. 49 



These observations were based on a dozen medium-sized Axolotls (and as 

 many controls) of the albino variety, in which the pigment cells are sparse 

 and confined to the upper surface of the head and mid-dorsal region. The 

 reaction was more, pronounced when the whole gland or the posterior lobe 

 alone was administered than when the anterior lobe only was used. While 

 these experiments were in progress Bennet Allen (1920) issued a preliminary 

 notification of experiments on pituitary removal and transplantation in 

 tadpoles, mentioning inter alia that animals after pituitary removal display 

 a silvery-white appearance, in marked contrast to the coloration of the 

 normal form. Thus the expansion of melanophores in reaction to the 

 pituitary hormones would not appear to be confined to Axolotls.* 



The interest of this reaction is twofold : firstly in relation to Spaeth's thesis 

 (1916) that melanophores represent a modified form of smooth muscle fibre ; 

 and secondly, in view of a suggestion by Fuchs (1906) that internal secretion 

 may underlie the well-known phenomenon of " colour adaptation." Spaeth 

 instances, as intermediate in character between typical smooth muscle and 

 pigment cells, the sphincter pupillse, in which, in certain cases, the cytoplasm 

 is densely charged with melanin granules ; he points out that the melano- 

 phores are mesodermal in origin ; and draws attention to a remarkable 

 parallelism between the reactions of the sphincter pupillae fibres and melano- 

 phores in response to electrical and light stimuli and chemical stimuli such 

 as atropine. To this it may be added that both react in the same way to 

 the pituitary hormone, for it has been shown by Cramer (quoted by Schafer, 

 1913) that the latter induces dilatation of the pupil. 



The phenomenon of " colour adaptation " in reptiles, amphibia and fishes, 

 has been provocative of much controversy and is little understood. It is 

 widely known that these organisms can respond to the colour of their sur- 

 roundings by pigmental changes. The most recent work of Laurens (1917) and 

 others shows that, though the melanophores respond directly by expansion 

 in bright light, in the case of Axolotls which have been blinded there is no 

 secondary modification of the response (partial contraction) after continued 

 illumination, and no power to respond to their background, e.g., to become 

 darker when illuminated only from above in a blackened container. The 

 pigmental responses of these animals thus appear to be under the control of 



* Allen's (and also Smith's) results indicate that it is the intermediate lobe of the 

 pituitary which is concerned in pigmental control in Anura. Presumably the same 

 holds good for the effect of a diet of Mammalian pituitary on the Axolotl. The 

 intermediate lobe will remain attached to the posterior lobe unless specially dissected 

 apart. Swingle's recently published work (1921) confirms and extends the above- 

 mentioned results. 



VOL. XCIII. — B. 



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