134 W. W. SWINGLE 



iridescent appearance so characteristic of the picture of albinism. 

 That is to say, the xantholeucophores are contracted and the 

 silvery appearance is lost, the animal appearing dark like normal 

 tadpoles. Hence, the picture of albinism is not so much due to 

 contraction of the corial melanophores as to expansion of the 

 overlying layers of xantholeucophores. This interpretation of 

 Smith's has recently been controverted by Atwell. 



In a recent communication ('20) Allen has reported a very 

 brief summary of his results with transplanting the pars inter- 

 media of the adult frog. He says: "Normal tadpoles into which 

 the intermediate lobe is engrafted become much more darkly 

 colored than the controls, while those which have been made to 

 turn white as a result of removal of the anlage of the hypophysis 

 exclusive of the posterior lobe are made to change back from white 

 to black when the intermediate lobe is engrafted into them." 



In view of these experiments and those recorded here, it can be 

 regarded as a well-established fact that in anuran larvae the pars 

 intermedia secretes a substance which exerts a powerful effect 

 upon the melanophores. The absence of the hormone results in 

 permanent contraction of many of these cells, and expansion of 

 the xantholeucophores, its presence in large quantities such as 

 follows transplantation of the glandular tissue, causes maximum 

 expansion of the epidermal and corial pigment cells and con- 

 traction of the bearers of guanine and xanthine. 



It has long been known that many conditions affect the melano- 

 phores of the frog skin; a list of such agencies includes temperature, 

 electric currents, variations in the intensity of light, and many 

 chemical substances aside from hormones. The effect of such 

 stimuli, however, is temporary and lasts only so long as the mel- 

 anophores are subjected to the influence of the agent. On the 

 other hand, in the case of the hormone of the pars intermedia of 

 the hypophysis, we are dealing with an internal regulating agent 

 of high potency, the effects of which are continuous, and not to 

 any extent influenced by changes in the environment. For in- 

 stance, engrafted larvae which have turned dark do not respond by 

 color change, to light stimulation, and neither do albino larvae 

 deprived of the pars intermedia. Smith has shown that the cor- 



