CHROMATOSOME-DISPERSING HORMONE 



causing dispersion of the melanosomes.' In fishes, as in am- 

 phibia, optic stimuli chiefly determine whether or not the 

 secretion will be released. 



Likewise in elasmobranch fishes, other authors have dem- 

 onstrated that hypophysectomy is followed by a cutaneous 

 pallor which persists irrespective of the background. Barry 

 (1937) described a dogfish {Scylliorhinus canicula)^ the cuta- 

 neous melanophores of which resembled those of a hypophy- 

 sectomized fish in respect of the unchanging concentra- 

 tion of the melanosomes and their rapid dispersion after the 

 injection of a pituitary extract. However, his description of 

 the histological appearance of the pituitary body and its re- 

 lated structures is of little assistance in explaining the phe- 

 nomenon. The removal of the pituitary from Torpedo 

 marmorata causes a light coloration of the skin as a result of 

 melanosome concentration (Veil and May, 1937). Vilter 

 (1937) attributed the "melanophore contraction" which ap- 

 pears as a result of hypophysectomy in two rays, Trigon 

 pastinaca and Raia undulata^ to a pronounced tonus of the 

 sympathetic nervous system because ergotamine, which may 

 cause paralysis of sympathetic terminal fibers, brought about 

 a marked dispersion of the melanosomes in either normal or 

 hypophysectomized fishes of these species.^ 



In teleost fishes the role of the pars intermedia in effecting 

 color changes by means of the melanosome-dispersing hor- 

 mone is less important and often is difficult to evaluate. Veil 

 recently stated (1937) that the removal of the gland from the 

 catfish {Ameiurus) is followed by blanching of the skin, which 

 can again be made dark by the administration of fish pitui- 

 tary or an extract of the mammalian posterior lobe. x'\ccord- 

 ing to Parker (1935), chromatosome dispersion in Ameiurus 



^ Neither the oxytocic nor the vasopressor hormone of the pars neuralis is re- 

 sponsible for melanosome dispersion. 



^ For years, epinephrine has been regarded as a substance causing melanosome 

 concentration. So far as fishes are concerned, it appears that the importance of a 

 sympathetic innervation of the melanophores is greater in teleosts than in elasmo- 

 branchs. 



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