92 



THE EYE IN EVOLUTION 



Epinephelus 



Triturus cristatus 



Phoxinus 



in a few days it can adapt itself to its habitat by becoming red, yellow 

 blue, green, white or black (Brown, 1935), a facility possessed in some 

 degree by several crabs ^ and Cephalopods.^ Such a change may occur 

 rapidly ; thus the larvse of butterflies (Brecher, 1922) and salamanders 

 (Kammerer, 1920) when placed under variously coloured glasses readily 

 change their hue ; and not only the tone of the general background but 

 its colour-pattern may be simulated with great fidelity by certain 

 teleostean fishes. The most remarkable changes of this type are seen 

 in the groupers (Epiriephelus) that swim over the variegated patterns 

 of the coral reefs in tropical waters and within a few minutes may 

 change a livery of bright blues and browns into an equally brilliant 

 costume of yellow and black ; a similar virtuosity is seen in flat-fishes 

 such as the fiounder, Paralichthys albiguttus (Kuntz, 1916 ; Mast, 

 1916). It is interesting that adaptation during the early stages of 

 development may play an important part in determining the final 

 pattern of colour in the adult ; thus if the larvae of the crested newt, 

 Triturus cristatus, develop on a dark background the yellow markings 

 of the adult become suppressed, if on a light background, the dark 

 markings suffer a similar fate (Lautz, 1953). It is to be noted that 

 all these reactions are completely dependent on the eyes and have 

 invariably been shown to be lost if the animal is blinded or even if it 

 is dazzled by a blinding light which abolishes the contrast between 

 the dorsal and ventral portions of the retina (octopus. Prince, 1949). 

 (c) Occasionally indirect responses may follow stimulation of 

 receptor mechanisms other than the eyes — the mid-brain as in some 

 fishes {Phoxinus — Scharrer, 1928) or the pineal body as in lampern 

 larvae (Young, 1935) or teleostean fishes (Breder and Rasquin, 1950). 



AmmoccEte larva 

 of lamprey 



The central organization of these pigmentary changes is as varied 

 and complex as the variations in the colours themselves, and in view 

 of the multiplicity of the types of chromatophores and their reactions 

 it is not surprising that our knowledge of their control is by no means 

 complete in spite of much research. Apart from local primary 

 reactions, two methods of coordination are found, hormonal and 

 nervous, the first the more primitive and slower in its development, 

 the second the more elaborate and efficient. Sometimes the one is 

 present alone, as is seen, on the one hand, in the simple hormonal 

 control found in Crustaceans, the more primitive Fishes, frogs and 

 lizards, or, on the other hand, in the simple nervous control found in 

 the leech or the chameleon. More often the two are combined in a dual 

 mechanism of coordination, the hormonal control being sometimes the 

 preponderatiiig influence as in Insects or the eel, but usually being 



1 Portunus — Abramowitz (lOST)) ; Planes — Hitchcock (1941). 

 ■ Sepia— Kiihri and Heberdey (lSt29), Kuhn (1950). 



