88 



THE EYE IN EVOLUTION 



Figs. 60 and 61. — The Pigmentary Changes in the Stick-Insect, 



Dl XI FPUS. 



There are 3 types of pigmentation : (A) the cross-hatching indicates a 

 static layer of yellow-green pigment underneath the cuticle, (B) the fine dots 

 indicate red pigment which may be either aggregated into clumps or dis- 

 persed, and (C) coarse dots indicating brown-black pigment which migrates 

 from a deep site underneath the nuclei to a superficial position underneath the 

 cuticle (after Giersberg). 



'yn, 



^^ul>^--\^:-.i<-^^^^tmuj^ 



■' — B 



Fig. 60. — The epidermis in the light- 

 adapted stage. 



Fig. 61. — The epidermis in the dark- 

 adapted stage. 



Salmo triitta 



comprised of various fat-soluble carotenoids ^ contained in lipophores. 

 In Invertebrates (Crustaceans, Insects) the chromatophores are 

 frequently polychromatic since each may contain a variety of these 

 pigments — blue-green, orange, yellow and red — sometimes each with 

 a separate distribution within the cells.- In Vertebrates the chromato- 

 phores are usually monochromatic — red (within erythroxthores), yellow 

 (within xantho2)hores) or green ^ — one animal often having several types 

 of pigment in different integumentary cells (purple astacene and yellow 

 lutein in the brown trout, Salmo trntta, Steven, 1948). A third pigmen- 

 tary factor is found extensively both in Invertebrates and Vertebrates 



Figs. 62 and 63. — Colour Changes in the Lizard. 



Fig. 62. — The deposition of the melano- 

 phores in the brown state when the 

 branches of these cells extend into 

 the stratum germinativum. 



Fig. 63. — The lizard in the green con- 

 dition when the pigment is con- 

 centrated beneath the static pig- 

 ment in the superficial layers. 



The stratum corneum has been displaced from the section (Kleinholz). 



1 The carotenoid pigments are of wide distribution and great biological interest, 

 playing a part as sensitizers to the phototropic movements of plants, the phototactic 

 movements of animals, and also participating in visual processes. Their nature will be 

 discussed at a later stage (p. 118). 



2 In Crustaceans — Kiihn and Lederer (1933), Fabre and Lederer (1934) ; in 

 Insects — Schleip (1910-15), Giersberg (1928). 



3 See Fox (1947). 



