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 the 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 zone 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. 
