106 



KINETIC HORMONES — I 



own pars intermedia and can also be detected in effective quantities 

 in the blood of dogfish that have been kept on a black background. 

 There is still uncertainty about the presence of the antagonistic, 

 concentrating hormone, W, which is always more difficult to 



Light 



Light 



Dispersed 



Concentrated 



Fig. 3-23. Diagram of the nerves and hormones concerned in mixed 

 control of melanophores in the eel, Anguilla. Similar hormones act 

 alone in an amphibian such as Xenopus. An illuminated black 

 background is represented on the left and an illuminated white 

 background on the right. On black, only the floor of the retina 

 is stimulated by light and causes pigment dispersion, either by 

 stimulating the secretion of B (MSH) from the pars intermedia 

 (p.in.), or by adrenergic nerves (a.n.). On white, both the floor and 

 the upper part of the retina are stimulated and pigment is concen- 

 trated, either by secretion of B as before and of overriding W 

 (MCH) from the pars tuberalis {p.t.), or by cholinergic nerves 

 {cm.). In either case nerves from the eye pass through the brain 

 (C.N.S.) to transmit stimuli from the retina to the chromactivating 

 hormone or nerve (from Parker, 1943). 



detect. A full review of the literature relating to the chromatophores 

 of these and other fish has been given recently by Pickford and 

 Atz (1957). 



Teleostei. The control of melanophores in the teleosts is more 



