PHOTOPIGMENTS 



121 



Vitamin A^ has also been isolated in quantity from the eyes of a 

 number of marine Crustaceans,^ and the occurrence of this photo- 

 chemical system in the eyes of the king-crab, Limidus, and of Insects 

 has been corroborated by studies of their spectral sensitivity (Graham 

 and Hartline, 1935 ; Jahn, 1946 ; Granit, 1947 ; Jahn and Wulff, 

 1948 ; and others) and also by behavioural experiments (Weiss, 1943). 

 It is evident that more than one ty^e of pigment exists belonging to 

 the vitamin A^ family ; thus among the shrimp-like euphausiid 

 Crustaceans, Kampa (1955) isolated a pigment [Euj^hausiojisin) ^ with 

 a maximum absorption of 462 m/x, and in the deep-sea pra-wn, Pandalus, 

 an isomer was detected by Lambertsen and Braekkan (1955), It is 

 true that in some of these organisms astaxanthin may also be found ^ 



MO 

 Wavelength -ny^ 



Fig. 79. — Spectra of the Rhodopsin and Porphyropsin' Systems 

 Direct spectra of crude preparations from the retinae of the marine scup 

 (broken hnes) and the freshwater cahco bass (continuous lines). Rhodopsin 

 and porphyropsin are dissolved in 1 per cent, aqueous digitonin solution, the 

 retinenes and vitamins A in chloroform. All maxima have been brought to 

 the same height to facilitate comparison (Wald). 



but this pigment appears to take no part in the visual process and is 

 also distributed throughout the integument (Wald, 1941-46). 



Among Vertebrates the primitive Cyclostomes still retain the 

 vitamin A^ system (visual jDurple) (Steven, 1955) associated with their 

 retinal rods, as also does the majority of marine fishes ^ so far examined ; 

 on the other hand, most fresh-water fishes ^ possess a different 

 svstem based on vitamin Ao and retinenco. In Amphibians and hioher 



1 Crabs, lobsters and others, Wald (194.5-46), Fisher et al. (1952-5.5). 



^ Possibly related to or identical with the pigment absorbing maximally at 467 m/x 

 described by Dartnall (1952) in the tench. 



^ As in the fresh-water crayfi.sh, Caniharus virilis ; the shrimp, Aristeomorpha, 

 Grangaud and INIassonet (1950). 



^ Exceptions are found, for example, among the wrasse fishes {Labrus bergylta and 

 Tautoga onitis), the eves of which have a pigment based on the vitamin Aj svstem 

 (Bayliss et al., 1936 ; Dartnall, 1955). 



* An exception is the fresh-water bleak, Alburr^us lucidiis, which has, in addition 

 to two pigments based on vitamin A,, another probably ba.sed on Aj (Dartnall, 1955). 

 It is to be remembered, however, that only a few species have hitherto been examined 

 so that further iii\estigation may weaken this generalization. 



