BIOCHEMICAL EVOLUTION 339 



Marine fishes (Ai) Land vertebrates (Ai) 



Catadromous fishes (Ai > A2) 



\ 

 Anadromous fishes (A2 > Ai) 



Amphibia (A2 and Ai) 



Freshwater fishes (A2) 

 Lampreys (A2 and Ai) 



Ancestral vertebrates {Ao}) 



Fig. 90b — (Wald). Distribution of vitamins A^ and A2 in vertebrate retinas. 



from a continuous fine of fresh-water ancestors, possesses the porphyropsin 

 system. The use of vitamin Ag in the retina appears to be universal in 

 fresh-water Vertebrates and to extend as far back to the origin of the 

 Vertebrates as it is possible to penetrate. 



W. Bergmann has emphasized that a marked difference exists, (which 

 can be seen by reference to Table XXV) in the material extractable with 

 fat-solvents when we compare the Vertebrates and the Invertebrates : 

 there is a greater proportion of unsaponifiable matter in the latter. 



Moreover, Bergmann noted that if we consider the distribution of 

 sterols in animals, the greatest diversity of sterols is found in the most 

 primitive groups while in the most highly specialized, cholesterol is almost 

 the only one identified (Table XXVI). 



Among the sterols of the least specialized animals we find Cgg or C29 

 compounds. Sterols of this type differ in the type and degree of unsatura- 

 tion, and in the nature of the radical attached at C-24, etc. (Bergmann, 

 1952). On the other hand, from a series of studies by Haslewood and 

 co-workers, we see that in teleost fishes or Elasmobranchs, Amphibians, 

 crocodiles and alligators, in a lizard, in Chelonians (turtles and tortoises) 

 and in some birds, the bile salts contain C27, C28 (or possibly C29) alcohols 

 and acids whilst in snakes and mammals, substances of this type are not 

 found. But the presence of C24 bile acids has been demonstrated in snakes, 

 teleost fishes, mammals and birds, but not in Elasmobranchs, Batracians 

 or reptiles such as the Crocodilians and the Chelonians. 



In general, the C27, C28 and possibly the C29 bile salts go with a more 

 primitive phylogenic status than with that of the more specialized animals 

 which have C24 bile salts. 



