2o8 On Melanin [Dec. 



philus flavicornis Fabr.). Phisalix (1905) found that the color 

 changes in the integuments of the cock-roach larva {Phyllodromia 

 germanica) are produced in the same way. 



Miss Diirham (1904) obtained extracts from the fetal skins 

 of rabbits and guinea pigs of black and agouti origin, which, when 

 incubated at 37° for 10 days in the presence of tyrosin and one 

 milhgram of ferrous sulphate produced dark precipitates. When 

 the skins of red guinea pigs were used a red precipitate was formed. 

 Toluol was added as a preservative, and no coloration was pro- 

 duced in the absence of the ferrous sulphate. Although it is prob- 

 able that the animal pigments are the result of oxidase action, only 

 more extended research can show whether these colored precipitates 

 were produced by the action of different tyrosinases or whether 

 they were formed by some other reaction. It is obvious that the 

 agency which produced the red pigment was different from that 

 which caused the formation of the black precipitate. 



I have found in a study of the pigment formation in the meal 

 worm {Tenehrio molitor), the periodical cicada {Tibicen septen- 

 decim L.), and the Colorado potato beetle {Leptinoiarsa decemlin- 

 eata Say) that in each case the mode of pigment production is, in 

 general, the same but that there are individual peculiarities which 

 call for separate treatment. 



Two varieties of tyrosinase occur in the meal worm, one variety 

 being readily soluble in water and the other variety being charac- 

 terized by its insolubility in aqueous media. The insoluble enzyme 

 occurs in the larger quantity and is extremely active. When the 

 larva sheds its skin the characteristic color pattern is wanting and 

 the entire body appears creamy white. This nearly colorless appear- 

 ance is retained after death, providing that the oxidase has been 

 destroyed by heating to 70°-8o° or eise that the oxidation has been 

 inhibited by keeping the larva in an atmosphere free from oxygen, 

 or by immersion in water or oil. Subsequent exposure to atmos- 

 pheric oxygen causes the normal color pattern to develop, providing 

 that decomposition has not set in. 



The Colorado potato beetle forms a color pattern in the same 

 way in which the pigment is laid down in the integuments of the 

 meal worm, with the exception that no evidence of the presence 



