OCCURRENCE OF THE VITAMINS A G83 



proportion of the total vitamin A reserves in the body. For example, out 

 of a calculated total of 300 mg. of vitamin A in the tissues of the dog, only 

 4 (xg. or approximately 0.00]% of the total occur in the retinal pigments.^^ 



Marine fishes (At) Land vertebrates (Ai) 



Catadromous fishes (Ai > As) Amphibia (As + Ai' 



Anadromous fishes (A2 > Ai) 



Fresh-water vertebrates 

 (Vitamin A2) 



Arthropod and mollusc vision 

 (Vitamin Ai, retinenei) 



Invertebrate photokineses 

 (Pigments unknown) 



Protistan phototaxis 

 (Astaxanthin, other carotenoids) 



Plant photokineses 

 (Carotenes, xanthophylls) 



Fig. 1. The retinal pigments as related to phylogenetic development.*^ The 

 vitamin A components are now believed to be vitamin A aldehydes. 



On the other hand, the vitamin A content of the retinas of some species of 

 gold fish is almost as great as the total vitamin A in the rest of the body.^^ 

 In addition to the article of Wald*^ on carotenoids and vitamins A in photo- 

 reception, Granit^^ has ^^Titten an excellent review on this subject. 



" S. W. Clausen and A. B. McCoord, Unpublished results. Cited by R. J. Williams, 

 Vitamins and Hormones, 1, 236, 240 (1943). 



** R. Granit, Sensory Mechanisms of the Retina, Oxford Univ. Press, 1947. 



