174 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
The glaucous green patches on the wings of Colaenis dido are 
composed mainly of green and yellow, but there is also a faint develop- 
ment of about half of the blue and a still fainter trace of red. 
The iridescent blue-green ground color of the upper surface of the 
wings of Morpho menelaus, viewed in such a way that the light 
makes an angle of about 20? with the normal to the surface of the 
wing, gives a spectrum of green and blue about equally developed. 
The yellow ground color found on the upper side of the wings of 
Papilio turnus shows a continuous spectrum, in which the yellow 
seems to be rather more brilliant than in the normal spectrum of 
white light. 
The sepia-brown ground color of the upper surface of the wings 
of Cercyonis alope gives a spectrum which lacks only the blue-green 
and blue. 
(6) Summary of Results. The researches of Coste (9091) and 
Urech (93) have demonstrated that the colors of butterflies and 
moths may be produced by two causes: by the presence of an actual 
pigment, or by some structural effect. Some colors are due entirely 
to pigment, others to structural causes, and still others to a combina- 
tion of the two. 
Black, brown, red, orange, and yellow are invariably due to 
pigment. 
Green is usually due to a structural effect, but in a few cases there 
is a green pigment present, 
White, blue, and violet are almost invariably due to structural 
causes. 
In addition to these facts I have found that most of the colors 
which are displayed by Lepidoptera contain a surprisingly large 
percentage of black. Also they are usually not simple colors, but 
composed of a mixture of several different colors. It is remarkable 
that Natural Seleetion, which is generally assumed to have been one 
of the principal factors in bringing about the wonderful develop- 
ment of colors in Lepidoptera, has not been potent enough to make 
these colors purer than is the case in existing butterflies. 
II. Tur ESSENTIAL NATURE OF PIGMENTAL Cotor IN 
LEPIDOPTERA. 
(1) Pigments of Larvae. Poulton ('85) showed that the phy- 
tophagous larvae of Lepidoptera * owe their colour and markings to 
