CHAPTER IX 



THE PARS INTERMEDIA AND THE PARS 

 TUBERALIS; THE HORMONAL REGULA- 

 TION OF CHROMATOPHORES 



NEARLY all the experiments in amphibia lead to the 

 conclusion that the pars intermedia elaborates an 

 internal secretion which causes a dispersion of the 

 black pigment granules in the epidermal melanophores. As a 

 result, the cell outlines can then be identified more or less 

 completely, so that the change has often been called an 

 "expansion."' This internal secretion of the pars intermedia 

 can be identified not only in the pituitary of fish,' amphibia, 

 reptiles, and birds but also in the pituitary of mammals, in- 

 cluding man. The function of the hormone, except in am- 

 phibia and some fish, is not clear. It is thought by some to be 

 concerned in visual adaptation in forms like the mammal. 

 Certainly there is no experimental evidence supporting 

 Biedl's belief (1922) that the pars intermedia is a "metabo- 

 lism-gland." Therefore, except for the brief mention of a 

 few experiments dealing with possible functions of the pars 

 tuberalis, this chapter will be almost entirely concerned with 

 the behavior of chromatophores in relation to internal secre- 

 tion (s) of the pituitary body.^ 



The following are the chief chromatophores which may be 

 found in fish, amphibia, and reptiles: melanophores, leuco- 



» See Sumner (1933) and Mast (1933). Part of the terminology proposed by 

 Sumner is used in this chapter. 



^ Hogben and Winton (1922) were unable to detect the hormone in the "pitui- 

 tary" (subneural gland) of a tunicate {Ascidiella). 



^ An elaborate review of observations on the distribution and characteristics of 

 chromatophores can be found in Fuchs's article published in 191 4. 



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