170 bulli:tix: museum of comparative zoology. 



cases, leaving the wing white or colorless. Coste used as solvents 

 a number of strong acids and alkalis ; while Urech confined him- 

 self to the use of water, hydrochloric acid, and nitric acid. Their 

 results may be conveniently summarized as follows : — 



Ulack according to Urech is a pigmental color, for it may be dis- 

 solved out of the wings by means of hydrochloric or nitric acid. 



Broicii is usually insoluble in water, but is soluble in hydrochloric 

 or nitric acid. 



The red and, orange pigments of the Pieridae, Lycaenidae, 

 Xj-mphalidae, Zygaenidae, and some Papilios are soluble in water. 

 They are insoluble in water in the Sphingidae, Arctidae, Bombycidae, 

 Saturaidae, and Geometridae. 



Yelloic pigment is acted upon by reagents in almost the same way 

 as the red and orange, especially if both red and yellow appear upon 

 the same wing. It is soluble in the Pieridae, Lycaenidae, Xym- 

 phalidae, Satyridae, and some Papilios, but insoluble in the Sphin- 

 gidae, Arctidae, Geometridae, and a few Xoctuidae. 



^Vflite is usually a structural color, but can be dissolved out 

 from the wings of the Pieridae by water, being in this case, of 

 course, due to a pigment. 



Green pigment can be dissolved out by water in the cases of the 

 Pieridae, Lj'caenidae, and Geometridae. In the vast majority of 

 cases, however, it is a structural color. 



Violet and blue are almost always due to structural causes. In a 

 few cases, however, as in Smerinthus ocellatus, a blue pigment can 

 be dissolved out. 



We see, then, that black, brown, red, orange, and yellow are 

 usually due to pigment, while white, green, violet, and blue are gen- 

 erally due to structural effects. 



It is well known that the scales of Lepidoptera are essentially- 

 hollow, flattened sacs often inclosing pigment, and Burmeister ('78) 

 arrives at the conclusion, from a study of the scales in various spe- 

 cies of Castnia, that the pigment is for the most part attached to the 

 upper layer of the scale-sac, rendering it opaque, while the lower 

 layer receives less pigment and is, in consequence, a little more 

 translucent. 



(2) Structural Colon's owe their origin to the external structure of 

 the scales or wing-membranes and not to the presence of a pigment. 

 They are often caused by diffraction, due to the scales being covered 

 with fine, parallel striae. Some of the most splendid colors in the 



