LIGHT AND PIGMENTATION 



97 



Squalus — Parker, 1935-36) ; Teleosteans possess a double innervation 



with, in addition, pigment -dispersing fibres the action of which is 



mediated by acetylchoHne (the kilhfish, Fundulus — Parker, 1934 ; 



the catfish, Ameitirus — Mills, 1932, Parker, 1940-41 ; and other Squalus 



species). These two types of nerve correspond to the sympathetic and 



parasympathetic systems of warm-blooded animals since adrenalin 



blanches and acetylcholine darkens the eserinized animal (Giersberg, 



1930 ; Smith, 1931). Similarly, darkening of certain Teleosts (the 



giippy, Lebistes reticulatus) can be brought about by adding D-lysergic Ameiurus 



acid diethylamide to the water of the aciuarium (Cerletti and Berde, 



1955) (Figs. 70 to 72). At the same time, however, even in these 



Fig. 73. — The Effect of the Injection of Pituitrin on a Frog. 

 The right animal injected six hours previously witli pituitary extract 

 from a fietal ox ; left, control (Hogben). 



fishes some hormonal influence remains since pituitary extracts are 

 slowly efi:ective in denervated areas (Matthews, 1933 ; Kleinholz. 

 1935 ; Abramowitz. 1937). 



AMPHIBIANS were the first class of animals in which a humoral 

 control of colour was demonstrated, when P. E. Smith (1916) showed 

 that hypophysectomized tadpoles remain indefinitely pale. Although 

 there is some evidence of a mmor nervous influence in some species 

 such as the darkening of the leg of the toad, Bufo arenarwn, on section 

 of the sciatic nerve and its blanching on peripheral stimulation of the 

 cut nerve (Stoppani, 1942). it may be said in general that amphibian 

 chromatophores are essentially under humoral control. This is main- 

 tained by two antagonistic hormones elaborated in the pituitary- 

 hypothalamic system — a melanin-concentrating W-snbstance causing 



Bufo 



S.O. — VOL. I. 



