LOWER FISHES; DIURNAL RHYTHMS 537 



In still other ways, the amphibian phenomena differ from those of 

 teleosts. Blinded frogs, like normal ones, respond dermally quite inde- 

 pendently of light and darkness in situations which are warm and dry or 

 cold and wet. At moderate temperatures, in the presence of adequate 

 moisture, the melanophores of eyed frogs contract in bright light and 

 expand over dark backgrounds. But in darkness they also expand, instead 

 of contracting as in fishes. Blinded frogs expand their melanophores in 

 darkness, and these will contract only to a tiny extent if the animals are 

 then illuminated. However, Laurens found that in larvae {Amby stoma) 

 the reactions of blinded individuals were like those of blinded teleosts, 

 though markedly retarded as compared with normal larvae. The primitive 

 tendency of melanophores (as shown in teleosts and in young amphibian 

 larvae) is, as Parker has pointed out, to expand in the light and contract 

 in the dark. With age, the eye comes to be able to inhibit the expansion 

 in the light; and, in amphibians, the presence of the eye — if in its normal 

 location, at least — somehow causes or permits the melanophores to ex- 

 pand in the dark. 



By and large, the dermal color-changes of amphibians are nowhere 

 nearly so clearly adaptive to background as those of teleosts. This is even 

 more true of the lizards. Darkening in low temperatures, and blanching 

 at higher ones, are such predominant activities that Max Weber was 

 prompted years ago to suggest that in both amphibians and reptiles the 

 dermal changes are designed primarily to regulate the temperature of the 

 animal, by adjusting the light-absorbing capacity of the skin. We will 

 consider this theory shortly when we come to the reptiles. 



Dermal Changes in Lower Fishes, and 'Diurnal Rhythms' — The 



seemingly paradoxical physiological kinship of the Amphibia and the 

 elasmobranch fishes, manifested in various other ways, is also borne out 

 by the character of color-change control. Color changes in elasmobranchs 

 went unnoticed until less than a decade ago. These fishes are generally 

 grayish or neutral in garb; and though they are sometimes stated to have 

 no typical melanophores, they are capable of changes in shade. The eye 

 operates these changes by way of the pituitary in all the investigated 

 species except one, wherein the blanching process (though not the dark- 

 ening) seems to be under the direct control of the nervous system. No 

 morphological changes are known to take place in elasmobranchs. 



We do not know much about color changes in other 'lower' fishes. At 

 least two of the three lungfishes (Protopterus and Lepidosiren) have 

 them, but their operation has not been investigated. In 1935 Young 



