172 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
and interference colors also. In addition, he points out the interest- 
ing case of certain Lycaenidae where the scales exhibit to the eye 
only interference effects, and yet a pigment can be dissolved out of 
them by the use of water. 
(4) Quantitative Determination of Pigmental Colors. I have 
analyzed the colors of many butterflies by means of the spectroscope, 
and also by Maxwell’s dises. As is well known, Maxwell’s dises are 
colored circular dises of cardboard, perforated at the center and slit 
along a radius so that two or more of them may be slid over each 
other, thus exposing different proportions of each. Then by rapidly 
rotating them the colors become blended, and thus it becomes 
possible to match any color, and to discover its fundamental con- 
stituents. By this means I have determined that the vast majority 
of the colors found in Lepidoptera are impure; that is to say, they 
contain a large percentage of black. 
For example the white of the upper surface of the wings of the 
common Pieris rapae consists of: 17% black, 13% emerald-green, 
10% lemon-yellow, and 60% white. 
Also the so-called “blacks” found in butterflies are rarely jet-black, 
but, almost always, only deep shades of brown. For instance the 
deep brown color of the under surface of the wings of Heliconius 
melpomene consists of 93% black, 3% lemon-yellow, 3.5% of 
Maxwell’s fundamental red (vermilion), and 0.5% of von Bezold’s 
fundamental blue-violet. 
The purest color I have met with is the canary-yellow ground 
color of the wings of Papilio turnus, which seems to consist of 
white light with the addition of a little yellow. 
Other colors all possess considerable black. Thus the glaucous 
green of Colaenis dido consists of black 29%, vermilion 24%, 
emerald-green 87%, von Bezold’s blue-violet 10%. 
The sepia-brown ground color of Cereyonis alope consists of black 
71%, vermilion 21.5%, emerald-green 7.5%. 
The tawny rufous color of the wings of Mechanitis polymnia, ete., 
is made up of black 46%, vermilion 40%, lemon-yellow 14%. 
The rufous red patch on the upper surface of the fore wings of 
Heliconius melpomene is made up of black 27%, vermilion 66.5%, 
lemon-yellow 6.5%. 
The yellow of the fore wings of Mechanitis polymnia consists of 
lemon-yellow 67%, emerald-green 14%, and white 19%, 
