OP ARTS AND SCIENCES. 243 



only the main yellow color of the body to the hypodermis (Leydig, 

 Histiol., p. 114). A jiarticular main color of the cuticula is assumed 

 by Grabcr (p. 17), which is said to change the underlying hypodermal 

 colors. As far as my studies go, the color of tlie cuticula is often 

 somewhat yellowish with a brownish shade, and only the most super- 

 ficial layers contain pigments, which therefore must have been pro- 

 duced during or directly after the casting of the skin. The layers 

 below the superficial ones were of indifferent color and had nothing 

 to do with the main color of the insect (thorax of Phanccus carni- 

 fex). Whether this is generally true will be proved by farther 

 observations. 



The second kind of colors belongs to the hypodermis, and are called 

 hypodermal colors. I consider them to be the consequence of a 

 chemical process, generating color out of substances contained in the 

 body of the insect. These colors may be changed into other colors 

 by light and heat, perhaps by acids or by the influences of the sexual 

 organs. If such a change were to a certain extent a photographic 

 process, some important facts (mimicry) could be understood, which 

 otherwise are inexplicable. 



The dermal colors are red, brown, black, and all intermediate shades, 

 and all metallic colors, blue, green, bronze, copper, silver, and gold. 

 The dermal colors are easily to be recognized as such, because they 

 are persistent, never becoming obliterated or changed after death. 

 Dermal colors are not unfrequently retained by insects inclosed in 

 copal, but never by fossil insects inclosed in amber. The persist- 

 ence of dermal colors is easily understood, as they are formed before 

 the chitine becomes rigid, and later are preserved in a similar manner 

 as if they Avere inclosed in hermetically-sealed glass tubes. 



The hypodermal colors, placed in the soft and not chitinized hypo- 

 dermis, are easily recognized, because they fiide, change, and disappear 

 after death. A fresh or living insect, when opened, can easily be 

 deprived of the hypodermal colors, simply by the action of a small 

 brush. An important exception is to be made in certain cases, in 

 which hypodermal colors are persistent after death as well as dermal 

 colors. In such cases the colors are better protected and inclosed 

 nearly air-tight. I refer to certain colors of the elytra and wings, of 

 the hairs, scales, and appendages of the body. The elytra and wings 

 are, as is well known, at first open bags in direct communication with 

 the interior of the body. The hairs and scales are at first similar 

 open bags, glued together only at a later period. In all of them the 



