The Origin of the Brown Pigment in the Integuments of the Larva of Tenebrio Molitor

The question as to the cause of melanin formation has given rise to considerable investigation and much speculation, but it is only recently that the theories and the known facts have begun to coincide. Earlier investigators held that the melanin formation in red-blooded animals was due to products formed from the haemoglobin, but this failed to explain why iron was only a casual constituent of the melanin ash. More recently the melanins have come to be looked upon as having an origin in the albumen. especially in those products with an aromatic or heterocyclic neucleus (tyrosin, tryptophan, etc)‘. Compounds of this class when oxidized by artificial or naturally occuring oxidases undergo a series of color changes, ending in the case of oxidases of the tyrosinase type2 with the deposition of a dark, insoluble, melanin-like body. Shortly after the discovery of tyrosinase by Bertrand3 it was suggested that the oxidases, acting on various substituted aromatic or heterocyclic phenols, were the cause of melanin formation and this view has been gen-