OF ARTS AND SCIENCES. 245 



abdomen of a female is cut off, tlie fluid contained in the body by its 

 contact with the air changes directly to a white shade, which seems to 

 be of the same nature as the external secretion. Therefore this 

 white secretion would not be strictly derived from the hypodermis, 

 except that it is secreted by hypodermal glands. I am not sure 

 whether some of the colors before mentioned may not be in some way 

 different from the others. In the case of Lixus I find it stated that 

 the mealy powder, when taken off, is renewed in a few days. I cou- 

 fess that my opinion concerning those external colors is not yet en- 

 tirely settled. That those colors are simply an exudation of fluid 

 in the body through the pore canals is not to be accepted ; they must 

 have been changed in passing through the hypodermis. In such Lepi- 

 doptera as become oily after death, the fat exudes through the pore 

 canals, and, passing through the hypodermis, reaches the outside of 

 the body unchanged. A chemical investigation would be very desira- 

 ble, and would perhaps give some better explanation ; but the quan- 

 tity which may be had of those colors is always too small for such 

 a purpose. The blue mealy matter of the abdomen of Odonata when 

 scratched off and brought in contact with ether on a glass slide is 

 directly dissolved, leaving scarcely a margin around the spot after the 

 evaporation of the ether. When the same matter on a glass slide 

 is held over a candle, it melts directly, and after drying a dull whitish 

 spot is left. 



Bezold's Views upon the Nature of Colors. 



Recent investigations about the nature of colors advance also our 

 knowledge of the colors of insects. The Theory of Color in its Rela- 

 tion to Art Industry, by W. von Bezold,* contains some excellent 

 statements, which allow us to understand better the colors of insects. 



1. " Transparent colors, so called by artists, are similar in their action 

 to colored glass or to clear-colored solutions. When the light falls 

 upon a shining surface of such colors, a reflection primarily takes 

 place at the upper surface, extending only to a fraction of the impin- 

 ging light; the remainder enters the colored mass, and there undergoes 

 a process of absorption, so that it is already decidedly colored wlien 

 it arrives at the ground-surface of the layer. If at this second sur- 

 face the light strikes upon a white body which reflects irregularly, 



* Dr. W. von Bezold : The Theory of Color in its Relation to Art and In- 

 dustry. Translated by S R. Kiihler, Boston, 187G, &c. 



