OF ARTS AND SCIENCES. 263 



Perhaps there exists some stronger acid in some insects. One 

 observation made by myself can scarcely be explained in any other 

 way. A large species of Mygale, having been many years in alcohol, 

 was taken out of it and exposed on a glass slide near the stove to a 

 moderate heat. When it was dried, I was astonished to find the whole 

 slide injured by a corrosive acid. Examined with the microscope, the 

 surface of the slide was covered all over with fine short and mostly 

 parallel lines, rough as if cut out with a diamond. As there is no 

 acid known which injures glass, fluor acid excepted, the fact cannot 

 be explained ; but I am quite sure that I was not mistaken in my 

 observation. 



I am not able to give any further statements on fat, fat acids, and 

 other acids, because nothing more is known about them. My conclu- 

 sions are as follows: — 



It is certain that a color (indigo) is produced as result of the diges- 

 tion of albumen. 



It is certain that fat is produced by digestion out of albumen. 



It is certain that colors of insects are combined with fat. There- 

 fore it seems probable that the colors of insects are chemically pro- 

 duced by a combination of fats or fat acids with other acids or akalis 

 by the influence of air, light, and heat. 



It should not be overlooked that anilin is the product of a distilla- 

 tion of the oily parts of coal or peat. Colorless anilin has no alkaline 

 reaction, but neutralizes acids. Everybody knows the variegated 

 and beautiful colors originating from anilin combinations, and it is 

 not a daring conclusion to presume that colors of animals and plants 

 have a related origin and nature. I am assured by Professor W. 

 Hempel, Dresden, Saxony, that in the Gulf of Naples a moUusk has 

 been found which contains aniline colors. 



The very obvious question, " Does the food have any influence on 

 the colors of insects ? " is answered as often in the afllirmative as in the 

 negative.* I have stated before that Spliingid caterpillars fed on 

 plants placed in salt water showed colors different from the caterpil- 

 lars fed with the same plant placed in fresh water. But the imago 

 showed no difference whatever. On the other hand, the imago of the 

 American Hemileiica maja shows the typical black form whenever 

 the caterpillar feeds on Quercus ilicifoUa^ as in Massachusetts, New 



* R. MacLachlan, Entom. Weekly Intelligencer, London, 1861, No. 254 ; 

 Variation caused by the Food of the Larva does not exist." 



