226 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
3. The probable Chemical and Physical Nature of the 
Pigments of Lepidoptera. 
Only a beginning has, as yet, been made in the study of the nature of 
the pigment substances that are found within the scales of Lepidoptera. 
Coste (90-91) and Urech (93) have carried out extensive series of 
experiments, which show that many of the pigment substances may 
be dissolved out of the scales by means of chemical reagents, giving 
colored solutions, and leaving the scales white or colorless. They have 
also shown that some of these pigments may be changed in color by 
the action of reagents, and then restored to their original color by 
the use of other reagents. For example, many reds are changed to 
yellow by the action of HCl or HNO;, and may be restored to the 
original red color by the use of ammonia. Their researches show that 
reds, yellows, browns, and blacks are always due to pigments. In a few 
cases, greens, blues, violets, purples, and whites are also due to pigments, 
and not, as is usually the case, to structural conditions, such as striz 
upon the scales, etc. 
It is probable that the most universal pigment colors to be met with 
in the Lepidoptera are the yellowish-buff and brown-drab tints, and this 
is especially true of the nocturnal forms. The diurnal forms have almost 
a monopoly of the brilliant reds and yellows and the rich blacks, but it 
is interesting to note that yellowish-buff or brown tints are still very 
common upon those portions of their wings that are hidden from the 
light, such as the upper costal edge of the hind wing, which is usually 
concealed from view beneath the overlapping fore wing. Wallace (89, 
p. 274) has called attention to the fact that a yellowish or buff tint is 
one of the commonest and most widespread colors in Lepidoptera. 
Concerning the chemical nature of the pigment substances within the 
scales, but little has as yet been made known. Hopkins (’89, 791, 794) 
finds that the white pigments in the Pieridze are due to uric acid, and 
also that the red and yellow pigments are due to two closely related 
derivatives of uric acid. These uric acid derivatives used in ornamen- 
tation are apparently confined to the Pieridée among butterflies. For 
when a Pierid mimics an insect of another family, the pigments in the 
two cases are chemically quite distinct. This is well seen in the genera 
Leptalis (Pieridee) and Mechanitis (Danaidz). 
Further, Griffiths (?92) has shown that the green pigment found in 
several species of Papilio, Hesperia, and Limenitis among butterflies, and 
