64 



BIOCHEMICAL SYSTEMATICS 



Fig. 4-4. Transfer from the porphyropsin to the rhodopsin system 

 during metamorphosis of the bullfrog. Antimony chloride tests 

 with extracts of bleached retinas from tadpoles approaching meta- 

 morphosis, and from newly emerged frogs. The tadpole retina 

 contains a high concentration of vitamin A2 with only a trace of 

 Ai, the frog retina just the reverse pattern (Wald, 1945-46). 

 Reprinted from the Harvey Lectures by permission of the Academic 

 Press, Inc. 



icant information, for tadpoles have mostly porphyropsin 

 with only a trace of rhodopsin, while the frogs have mostly 

 rhodopsin. Intermediate stages exhibit mixtures (Fig. 4-4). 



Wald says, "It is difficult to view this [latter] phenomenon 

 otherwise than as a recapitulation." This work is of unusual interest 

 to biochemical systematics. In the first place, at the major systematic 

 category level it provides modest further support for the argument 

 that freshwater fishes are the most primitive and that they were the 

 progenitors of amphibians. 



However, at the lower systematic category level it provides 



