528 ADAPTATIONS TO PHOTIC QUALITY 



whatever visual consciousness a fish may possess. More recently Brown 

 and Thompson have shown that in eight species of freshwater fishes, in- 

 dividuals adapted to pale or dark backgrounds would prefer the respec- 

 tive backgrounds when allowed to make a choice. But the color changes 

 mediated through the eyes are just as mechanically reflex as is the visceral 

 disturbance we may experience from certain shifting patterns of visual 

 stimuli which we cannot even recognize or describe. 

 Physiological Color Changes in Teleosts — Of all fishes — indeed, of 

 all vertebrates — it is the teleosts which display the greatest versatility in 

 both physiological and morphological changes of costume. And, it is 

 these forms whose chromatophoral performances are most wholeheartedly 

 devoted to fitting the animal to the pattern of its surroundings. Many 

 marine forms, like the swordfish and tuna, do have relatively inert color- 

 ations. Very probably this is because, being pelagic, they are never near a 

 substrate or background and have no need of a capacity for adjusting 

 thereto. But many littoral fishes, particularly marine ones and especially 

 the hordes of tropical coral-reef species and the rock-reef fishes of the 

 temperate zones, can manipulate their colorations with real virtuosity, 

 and may match their backgrounds closely. The groupers (genus Epi- 

 nephelus) have been called the chameleons of the sea — which is a gross 

 under-compliment since the true chameleons actually have less of a 

 dermal repertoire than a tree-frog. Some of the flatfishes are not far be- 

 hind the coral-reef fishes. The rapidity of their shifts of color as they 

 glide over a variegated pattern has been called 'blush-like'. One Nassau 

 grouper in a New York aquarium was observed to don eight radically 

 different liveries within a period of a few minutes. Beebe has described 

 a fish which he watched as it swam in amongst some coral and out again. 

 When it went in, it was a shining blue with three vertical brown bands. 

 When it came out a few moments later it was a brilliant yellow, thickly 

 covered with black polka-dots — and Beebe was able to assure himself 

 that it was really the same fish. 



There are species in which portions of the whole color pattern reside 

 in internal organs (peritoneum, meninges, etc.). These colorations show 

 through to the surface owing to the transparency of the overlying struc- 

 tures, and are blended with patches of dermal color to form the overall 

 pattern of the fish. This is the situation in Coryphopterus glaucofrcenum ; 

 but in Eviota personata all of the color pattern is internal, the muscles 

 and bones are transparent, and there is but little pigment in the skin. 

 These internal colorations change in sympathy with, and in cooperation 



