236 PROCEEDINGS OP THE AMERICAN ACADEMY 



The Color. 



As most insects are more or less colored, color is an impor- 

 tant character. I have said purposely insects, and not arthropods, 

 because my studies have not extended to the other groups. Some 

 facts, of course, can be applied to all ; but the other groups are not 

 to be compared for the frequency and for the intensity of the 

 colors with those of insects. There is no doubt that the different 

 colors of insects are the consequence of the contact of the animal 

 with air and light ; or at least that colors are more strongly devel- 

 oped by both these factors. The only contrary statement known to 

 me is by Professor Sachs, and will be considered later. The influence 

 of light is proved by the colorlessness of cave insects, of the larvae 

 living in the earth or in the interior of plants or animals, even by 

 some insects living only a very short time in the open air, as certain 

 very small Pllphemerina and Diptera. It is proved by these facts that 

 colors of organic bodies, plants, and animals are found prominently in 

 their external coverings. Therefore the Greek philosophers consid- 

 ered color to be the product of a chemical action, called by them 

 mxpig, boiling. The interior of organic bodies is mostly colorless or 

 discolored. There exist, indeed, exceptions even in insects, but at 

 least a part of these internal colors is to be found in places which are 

 in contact with the air. The trachea in Odonata and others are red ; 

 the fat body in Trichois red, in Zerene yellow, in Pentatoma green ; 

 the Malpighian vessels in some Orthoptera green ; the testicles in 

 some Hemerobina, at least in the previous stages, lemon yellow ; the 

 anal glands in Osmylus black ; the blood in Chironomus red. In other 

 orders we find some internal organs of Ilolothuria brick-red, of Echi- 

 nus yellow. After all, we are justified in considering those cases as 

 exceptions, or even as rare ones. 



Besides air and light, there is a third factor influencing the develop- 

 ment of color, heat and its counterpart, cold. The heat has a well- 

 known prominence in all chemical processes, and of course also in 

 colors if they are the result of a chemical process. The carbonizing 

 of tissues gives to them a certain color by the change which follows 

 the combination of the tissue with oxygen. Such colors arc very 

 common, and of different intensity in insects. The brown or black 

 color of many chrysalids, which are inclosed in a cocoon not perme- 

 able to the rays of light, is probably the product of carbonization. 

 The importance of heat and of cold for the production of colors in 



