URIC ACID 193 



and Raper, render it probable that dopa is the initial product of 

 the action of tyrosinase upon tyrosin. 



4. Pigments with Purine Bases. Hopkins, in his well-known 

 researches on the chemical nature of the pigments of the Pieridse 

 (1896), showed that the white and yellow colours in the wing 

 scales in these butterflies are due to uric acid and its derivatives. 

 Subsequent workers have confirmed this general conclusion and, 

 so far as is known, the Pieridae are the only family of butterflies 

 which have the property of depositing uric acid in the wings. 

 Wigglesworth (1924) has made a quantitative study of this sub- 

 stance in Pieris hrassicce and finds that part of the uric acid, 

 contained in the fat-body of the pupa, becomes deposited in the 

 wings just before emergence of the perfect insect. More of it 

 becomes transferred to the alimentary canal, from which it is 

 voided to the exterior. Estimations of the amount of uric acid 

 present in the wings of the two sexes showed a markedly greater 

 quantity in the male. There appears to be no actual constant 

 difference in the uric-acid content of the two sexes, and the excess 

 present in the male is due to the larger size of the wing scales, 

 and hence their greater capacity for storing this substance. 

 Wigglesworth further investigated the same problem in Vanessa 

 urticce, a member of the family Nymphalidae. In this species it 

 was found that the total amount of uric acid present is approxi- 

 mately the same as in P. hrassicce, but that during development 

 it is, in part, passed to the digestive canal, but not to the wings. 

 Schopf and Wieland (1926) have further studied the white wing 

 pigment in Pieris hrassicce and in P. napi and, while agreeing in 

 its similarities to uric acid, claim that it differs from that substance 

 in certain of its reactions. It consists according to them of a 

 special compound which they term leucopterine. The same 

 authors (Wieland and Schopf) also examined the yellow pigment 

 of another Pierid, viz., Gonejpteryx rhamni, and gave the name 

 xanthopterine to the uric acid derivative, of which it is composed. 

 Tliis name is apparently given to the same pign\ent which Hopkins 

 termed lepidotic acid. 



Uric acid and its derivatives are the end products of purine 

 metabolism in insects, and are formed as the result of the decom- 



R.A. ENTOMOLOGY. 7 



