VII THE COLOURS OF THE LEPIDOPTERA 151 



in hot water, forming a bright yellow solution with 

 a green fluorescence. The pigment is insoluble in 

 organic solvents, is acid in reaction, precipitates on 

 cooling the watery solution, and gives the murexide 

 reaction. It thus belongs to the uric-acid group, and 

 has been called lepidotic acid by Hopkins. As 

 already stated, it occurs as one of the ordinary 

 waste products of the organism, at the time of the 

 emergence from tfie pupa. It is a derivative of uric 

 acid, and can be artificially produced by heating uric 

 acid with water in sealed tubes to a high temperature. 

 It is somewhat interesting to note that by heating 

 the yellow pigment with dilute acids in a water-bath, 

 Hopkins obtained a purple colouring-matter, yielding 

 a spectrum with two bands. This pigment does not, 

 however, appear to occur naturally, unless the purple 

 tips of the fore-wings of Anthocharis ione be due to it. 

 Although uric and lepidotic acids frequently occur 

 in the same wing, Mr. Hopkins believes they never 

 occur in the same scale ; pale yellow patches are 

 due to a small amount of pigment in the scales and 

 not to an intermixture of the two acids. Orange 

 patches are due to a large amount of the yellow 

 pigment, but red ones are due to the presence of a 

 red pigment. They yield their pigment to hot 

 water, but the aqueous solution is yellow. On 

 evaporation this solution yields, however, a red 

 residue. The residue gives the murexide reaction, 

 and also yields the purple substance, lepidoporphyrin, 

 just as the yellow does. Mr. Hopkins (1892) is of 

 opinion that the difference between the red and 

 yellow is either purely physical or due to the 

 association of the yellow acid body with a base. 



