172 BULLETIN: ]VrUSEUM OF COMPARATIVE ZOOLOGY. 



and interference colors also. In addition, be 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 b}' the use of water. 



(4) Quantitative Deter ndaation of Pigrnental Colors. I have 

 analyzed the colors of many butterflies by means of the spectroscope, 

 and also by Maxwell's discs. As is well known, Maxwell's discs are 

 colored circular discs 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 bro^vTi 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 "\vith 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 37%, von Bezold's blue-violet 10%. 



The sepia-brown ground color of Cercyonis alope consists of black 

 71%, vermilion 21.5%, emerald-green 7.5%. 



The tawny rufous color of the wings of Mechanitis polymnia, etc., 

 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%. 



