COLORATION IN POUSTES. 47 



of large oval granules. These by their disintegration gradually spread 

 over contiguous areas, the pigment meanwhile diffusing into the sur- 

 rounding unpigmented chitin which has likewise been deposited from 

 the hypodermal cells. 



From the relation existing between the pigmented areas and the 

 muscles, it is evident that the pigmentation is influenced by the meta- 

 bolic process accompanying the development of muscle. Needham (18) 

 considers that the nuclei of the disintegrating cells of the fat body pass 

 directly over into the nuclei of the developing muscles. Nothing is 

 definitely known concerning the nature of the chemical process involved 

 here ; but it would seem probable that in such a region substances would 

 be produced which, through the medium of the hgemolymph, would affect 

 the action of the hypodermal cells, modifying the product of their 

 activities, and at the same time performing the function of excretion 

 for the organism. 



CHEMICAI, EXAMINATION OF THE PIGMENT. 



Chitin has long been known as one of the most resistant of organic 

 compounds. It withstands boiling in alcohol, ether, alkalies, and 

 dilute acids ; consequently the colors which it contains are extremely 

 difficult of isolation and analysis. The strong acids, such as HNO 3 , 

 H 2 SO 4 , and aqua regia, which dissolve the chitin, completely oxidize the 

 pigments and render the determination of their nature entirely out of 

 the question. 



The color changes, however, which the pigmented chitin undergoes 

 when boiled with acids and alkalies are extremely suggestive and give 

 some clue, I think, to the probable constitution of these pigments. If 

 the chitinous integument of P. variatus be boiled with yellow nitric 

 acid or aqua regia, it becomes oxidized, and meanwhile passes through 

 the following series of color changes : The dark areas become pro- 

 gressively lighter, passing through deep red-brown, red-brown, orange- 

 red, orange, orange-yellow, and pale yellow. Finally, just before total 

 decomposition, the chitin becomes perfectly transparent and colorless. 



Treatment of this acid-solution of chitin and pigment with am- 

 monia throws down an orange-brown crystalline precipitate. If, how- 

 ever, the transparent areas of chitin be similarly treated, no color 

 changes will be produced. Treatment of a solution of such areas with 

 ammonia produces a transparent precipitate. 



When this process of oxidation is interrupted at any stage and the 

 mass thoroughly washed in water, the color of the stage persists in- 

 definitely. Further, when the process of oxidation is interrupted at 

 any stage, as just described, and the mass is treated with ammonia or 



