52 COLORATION IN POLISTES. 



The similarity between the two reactions with NH^OH would point 

 in the direction of the derivation of the pigment from proteid. It is 

 possible that the partial oxidation occasioned by treating the proteid 

 with HNO3 and thus producing the yellow flakes is analogous to the 

 process by which the yellow pigment is derived from the protoplasm. 

 Similarly the further reaction by NH^OH may be paralleled in the 

 processes of reduction by which the darker pigments are derived. 



There is no reason why compounds of the benzene series should not 

 occur in these pigments, and especially if these are of the nature of 

 excretory products ; for phenol (CgH^OH) is a normal constituent of 

 the urine. Other aromatic compounds occurring in the body and con- 

 sidered to be products of proteid decomposition are indol or benzo-pyrol 

 (CgHjN) and skatol or B-methyl-indol (CgH^CHaNH) . These undergo 

 union with the oxy-group, and are further paired with H._,SO^ before 

 being excreted as ethereal sulphate and ethereal skatoxyl sulphuric acid. 

 Chitin (C,5H2eN.,Oio) itself is considered to be an amido-derivative of a 

 carbohydrate, with the formula /z(Ci2H,„Oio). The reducing agent is 

 a nitrogenous body, glucosamine, which is an amido derivative of grape 

 sugar (CeH,A— OH+NH, = CeH,„N05+ 3H). 



If the pigments occurring in Polistes are related to one another by so 

 small a difference as the addition of one or two NH.^ groups, and the 

 hypodermal pigment is an elaboration from the protoplasm of the hypo- 

 dermal cells, it may readily be imagined how slight differences in 

 metabolism in certain regions of the body, combined, perhaps, with 

 certain external influences, such as humidity and temperature, may 

 produce the range of variation in color and amount observed in the 

 darker pigments of these species. 



Comparison with the Color Phenomena of Butterflies. 



The succession of colors here is the same as that observed in the 

 developing color pattern of butterflies (Mayer, 17). The first colors 

 to appear in the ontogeny and the phylogeny of this group are the 

 yellows and drabs, which are also the simplest in molecular constitu- 

 tion ; the last to appear are the more complex blues and purples. All 

 of these colors are displayed by the various azo-compounds. The reac- 

 tions which Mayer gives suggest similarities with these compounds. If 

 such a relation does exist, we are perhaps nearer an explanation of the 

 striking phenomena of coloration observable here than we have hereto- 

 fore suspected. 



