CHROMATOSOME-DISPERSING HORMONE 



Chromatosome dispersion is caused by a secretion of the 

 pars intermedia or of the pars glandularis in animals other- 

 wise lacking the anatomical equivalent of the pars inter- 

 media.'^ The experiments of Hogben and Slome suggest that 

 a secretion of the pars tuberalis causes the opposite effect — 

 a concentration of the chromatosomes. 



The significance of the chromatosome-dispersing hormone 

 in vertebrates with functional chromatophores varies greatly. 

 In some fishes, e.g., dogfishes, the hormone may be the prin- 

 cipal means of chromatosome dispersion and, hence, of adap- 

 tation to dark backgrounds. In others, such as the catfish, 

 nerves also play a part in melanosome dispersion. Finally, 

 in a teleost fish like Fundulns^ the hormone is present in the 

 fish's pituitary but plays a negligible part in the regulation 

 of chromatosome distribution, which is largely under the con- 

 trol of nerves. In the fish Phoxinus laevis the erythrophores 

 and xanthophores are more specifically affected by the 

 chromatosome-dispersing hormone than the melanophores. 

 In amphibia like the frog the hormone appears to be the 

 principal means of effecting dispersion of melanosomes. The 

 action of the hormone in some reptiles — e.g., the lizard, 

 Anolis carolinensis — may be similar, but its importance in 

 normal animals has not been precisely investigated. Disper- 

 sion of either melanosomes or erythrosomes appears to be 

 due to the same hormone. 



The chromatosome-dispersing hormone can be extracted 

 from the mammalian pars intermedia or pars glandularis. A 

 substance with similar properties has been recovered from 

 the blood and urine of mammals. If the substance has a 

 function of importance to mammals, this has not been con- 

 vincingly demonstrated. There probably is no foundation for 

 the belief that melanosome-dispersing hormone can inhibit 

 diuresis. 



'sThe eye-stalks of Crustacea appear to be homologous with the pars intermedia 

 in this respect. 



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