192 THE FUNDAMENTAL ASPECT OF COLORATION 



papers (1921, 1922, 1925-26), and by Schmalfuss and his col- 

 laborators (1930, 1933) indicate that the chromogen in some insects 

 is " dopa " (dioxyphenylalanine), as in the elytra of Melolontha or 

 chater beetles, or dioxyphenylactic acid, as the mealworm 

 (Tenebrio). The processes by which the antecedents of melanin 

 are produced are unknown, but it has been suggested that the 

 production of this black pigment involves means for the disposal 

 of phenolic compounds which apparently are necessary for its 

 elaboration. The amount of melanin produced in an insect has 

 been shown to be modifiable by changes of temperature. This 

 has been demonstrated in the Ichneumonoid Habrobracon and 

 the effects, it is claimed, may be transmitted up to the second 

 generation of the offsj^ring {vide Schlottke, 1926 ; Kaestner, 1931). 

 Schmalfuss finds that an enzyme which, in the presence of oxygen, 

 converts dopa into melanin occurs in insects pertaining to five 

 different orders. Hasebroek claims that the chromogen involved 

 in certain black and brown pigmentations of the wings of Vanessa 

 antiopa is dopa. Melanising ferments appear to be generally 

 distributed among Lepidoptera, both in melanic and non-melanic 

 species and, according to Hasebroek, it is the chromogen that 

 is absent in non-melanic forms. Whether there is more than 

 one enzyme, e.g., tyrosinase, involved in melanin production is 

 extremely uncertain. Hasebroek (1921, 1922) maintains that 

 a dopaoxidase exists in certain Lepidoptera at a stage before 

 tyrosinase betrays itself. Thus, he states that the haemolymph of 

 larvae and of extracts of the eggs blacken when treated with dopa, 

 and not with tyrosin ; at a later stage, haemolymph from the 

 pupae and imagines exhibit melanin formation when treated either 

 with dopa or tyrosin. According to Przibram (1922), melanin may 

 appear in the cocoons of the moths Eriogaster lanestris and Saturnia 

 pavonia without the intervention of any enzyme. In these cases 

 the chromogen is dopa and he states that it differs from tyrosin 

 in that it produces melanin by direct oxidation in the presence of 

 moisture, provided the medium be alkaline. It may be said, 

 therefore, that the evidence of melanin production in insects, 

 although well established, is of an extremely conflicting nature. 

 The researches of the English biochemists, Onslow and Robinson, 



