1S7-2.] • 79 



The colors produced by the interference of light are only optical 

 phenomena, differing in this respect from the other colors of the 

 body, the epidermal and hypodermal colors. 



The epidermal colors belong to the pigment deposited in the cells 

 of the chitinized external skin, the epidermis. These colors are 

 mostly paetallic blue, green, bronze, golden, silver, black, brown, 

 and perhaps more rarely red. The epidermal colors are very easily 

 recognized, because they are persistent, never becoming obliterated 

 or changed after death. 



The hypodermal colors are situated in the non-chitinized and soft 

 layer, called hypodermis by Weismann. They are mostly brighter and 

 lighter, light blue or green, yellow, milk white, orange, and all the 

 shades between. The hypodermal colors in the body of the insect 

 fade or change, or are obliterated after the death of the insect. A 

 fresh or living insect w^hen opened may easily be deprived of the 

 hypodermal colors simply by the action of a little brush. I said 

 hypodermal colors in the body, because there are hypodermal colors 

 which are better protected, being encased nearly air-tight, and there- 

 fore are more easily preserved even after the death of the insect. I 

 refer to the colors in the elytra and wings, and in their appendages, 

 the scales. The elytra and the wings are, as is well known, at first 

 open sacs in communication with the body, of which they are only 

 the extension : of course they are formed of the epidermis and hjq^o- 

 dcrmis which become so strongly glued together after the transfor- 

 mation into the imago state -that a maceration of years tried by me 

 showed no effect at all on such wings. This fact is very interesting, 

 as it explains how wings, and even colored wings, can be found in 

 palaeontological layers in good preservation. The destruction of 

 insects, which is so peculiar to the secondary strata in England, 

 proves, as I believe, that the bodies of the insects must have floated 

 a very long time before they were deposited. It is quite a rarity to 

 find well preserved insects there, although many very well preserved 

 wings even of lace-winged flies have been described. 



There is an interval after the transformation before the mem- 

 branes of the wings become inseparably glued together ; it is at this 

 time that the finishing of the colors takes place. For instance in an 

 JEsclina, a LihelJula depressa or trimaculata, if the wing is cut off at 

 the base, the two layers can be easily separated by manipulation 

 under water, and the wing can be inflated with a little tube by sepa- 

 rating the bordei's with a knife. T can show specimens so pre|)ai'('(l. 



