PHOTOPIGMENTS 123 



however, to differ from the preceding, have been found in the eyes and also in the 

 integument of Arthropods among which they appear to have a wide distribution. 

 They have been most fully studied in the eyes and integument of Insects and were 

 first cursorily examined by Chauvin (1938-41). Becker (1939-41), studying these 

 pigments in the ommatidia of a number of insect sjaecies, gave them the generic 

 term ommochromes and subdivided them into ommins and ommatins. In 

 certain insects, such as the fruit-fly, Drosophila, for example, he described a 

 purplish-red pigment (erythrommatin) and a yellowish-brown (phgeommatin). 

 During pupal development the brown pigment appears first and the red later, 

 their appearance being determined by hormones, and one or other or both of 

 the pigments may be absent in certain stocks, the eyes appearing respectively 

 brown, red or white, ^ At a later date, however, Goodwin and Srisukh (1950) 

 and Goodwin (1950), working on locusts (the desert locust, Schistocerca gregaria, 

 and the African migratory locust, Locusta migratoria), concluded that these 

 pigments represented a redox complex, yellow when oxidized and wine-red when 

 reduced. For this variable pigment, or group of very closely related pigments 

 which are at the moment indistinguishable, they suggested the name insecto- 

 BUBIN, in view of its widespread distribution among insects. Whatever its 

 chemical nature, it is very resistant to chemical attack, bat has been isolated 

 as a reddish-brown powder which quickly changes into a stable dark brown 

 powder reminiscent of melanin, and shows characteristic absorption spectra 

 differing according to the method of extraction, whether measured in the fresh 

 extract or in tlie reduced or oxidized forni. 



Related pigments with similar absorption curves have been described in 

 crustaceans (the shrimps, Leander and Crangon — Polonovski et al., 1948 ; the 

 fresh-water Amphipod, Oammarus pulex — Michel and Anders, 1954). 



Such is the general evolutionary story of the photopigments ; it is a large 

 subject which will be discussed more fully when we deal with the physiology of 

 vision in a subsequent volume. In passing, however, it is interesting to note 

 that many years ago Patten (1886) put forward the theory that photoreceptors 

 were originally evolved, not as sentient organs, but as receptors of light-energy 

 for metabolic purposes as occurs in plants. He called them heliophags. The 

 theory, however, in its time raised a storm of criticism and never received 

 credence ; the most cogent evidence against it is the completely different 

 chemical nature of chlorophyll and the carotenoids and the contrast in their 

 functions — metabolism on the one hand, and photoreception or integumentary 

 coloration on the other. 



Augstein. Klin. Mbl. Augeuhcilk., 50 (1), Bernard. Quart. J. micr. Sci., 39, 343 



1 (1912). (1897). 



Bayliss, Lythgoe and Tansley. Proc. roy. Bliss. J. gen. Fhysiol.,26,^Ql (l9iS) ; 29, 



Soc. B, 120, 95 (1936). 277 (1946). 



Beadle. Gene^/cs, 22, 587 (1937). J. biol. Chcm., 172, 165; 176, 563 



Beadle and Ephrussi. Genetics, 21, 225 (1948). 



(1936). Bloch. Hoppe Seyl. Z. physiol. Chem., 9S, 



Becker. Biol. Zbl., 59, 597 (1939). 226 (1916-17). 



Naturwissenschaften, 29, 237 (1941). Bohn. Actions directrices de la lumiere, 



v. Bekesy and Kosenblith. Hb. e.vp. Paris (1940). 



Psychol. (Stevens), 1075 (1951). Braim and Faust. E.vperientia, 10, 504 



Benoit, Assenmacher and Manuel. C. R. (1954). 



Acad. Sci. (Paris), 235, 1695 (1952). Brecher. Z. vergl. Physiol., 10, 497 (1929). 



1 See Beadle and Ephrussi (1936), Beadle (1937), Ephrussi and Beadle (1937), 

 Mainx (1938), Ephrussi (1942), Ephrussi and Herold (1944), Wald and Allen (1946), 

 Villee (1947), Maas (1948), Okay (1948), Nolte (1954). 



