CHROMATOSOME-DISPERSING HORMONE 



some dispersion in the erythrophores of intact fish or of 

 isolated scales has again been used in recent experiments for 

 purposes of assay. 



The regulation of chromatosome dispersion in amphibia.^ — ■ 

 Especially in anuran amphibia past work has shown that 

 adaptation of the skin's color to dark or black backgrounds 

 chiefly depends upon an internal secretion of the pars inter- 

 media. After the removal of the pars intermedia (or the 

 neuro-intermediate lobe), marked aggregation of the melano- 

 somes takes place, so that animals like the frog remain pale 

 indefinitely, irrespective of the background. Atwell and 

 Holley (1936) found that the pars intermedia may be re- 

 moved from tadpoles, and yet sufficient tissue of the pars 

 glandularis is spared, so that in such silvery tadpoles com- 

 plete or partial metamorphosis occurs and normal develop- 

 ment of the thyroid, gonads, and adrenals takes place. The 

 authors suggested that the pars intermedia of tadpoles of 

 Rana syhatica can undergo development without contact 

 with nervous tissue. 



New studies by Hogben and Slome (1936) support their 

 conclusion that both the white- and black- background re- 

 sponses of the toad, Xenopus laevis, depend upon hormones. 

 Their study was limited to the dermal melanophores and 

 indicated that dispersion of the melanosomes is caused by a 

 hormone of the pars intermedia, whereas concentration of 

 the melanosomes is dependent upon an intact pars tuberalis. 

 Their results are summarized in Table 8. Presumably the 

 low sensitivity of the melanophores toward the melanosome- 

 dispersing hormone in animals without a pars intermedia (and 

 pars neuralis) is due to the pars tuberalis, the effects of the 

 secretion of which are no longer antagonized by the normal 

 secretion of the pars intermedia. On the other hand, the 

 great sensitivity of the melanophores of toads after the re- 



s The chromatosome-dispersing hormone can cause dispersion of the pigment- 

 granules in the melanophores of certain reptiles such as lizards (e.g., Anolis caroli- 

 nensis [Kleinholz, 1935]). 



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