CUTICULA COLORS. 1 35 



it is impossible to give formulae for the composition of these two layers of the 

 cuticula. This is a task for the organic and physiological chemist. Enough, 

 however, has been determined for the purposes of this paper. 



CHEMICAL EXAMINATION OF THE CUTICULA COLORS. 



In making the examination of the colors of these beetles I have used fresh, 

 dried, and alcoholic specimens of L. decemlineata, undecimlineata, multitce- 

 niata, rubicunda, dilccta, violescens, and signaticollis, and dried material of 

 zetterstcdti, lincolata, oblongata, signaticollis, and modcsta. The isolation of 

 the colors of these beetles is possible either by maceration, prolonged boiling 

 in water under pressure, or by oxidation in strong mineral acids. Inasmuch 

 as I have attained the same results by all three methods, I have made most 

 frequent use of strong mineral acids as solvents of these pigments. 



The method employed in preparing the pigmented material for extraction is 

 as follows : Crush fresh, alcoholic, or dried specimens in a mortar, add dis- 

 tilled water plus 1 per cent of KOH, and allow it to stand. Agitate at intervals 

 of an hour or two, and at the end of twenty-four hours pour off the water and 

 pound vigorously with a heavy pestle ; then wash in running water for sev- 

 eral hours, then in distilled water, and then dry. By this process all tissues 

 are removed, as are also the smaller appendages, and the result is a nearly 

 pure mass of chitin. L. decemlineata has proven the most satisfactory form 

 to work with on account of the ease with which one can obtain unlimited 

 material. 



It has been shown by Coste and Urech, and more recently by Enteman, 

 that the dark cuticula colors, when oxidized or acted upon by chemical 

 reagents, undergo a series of progressive and regressive changes. Thus Ente- 

 man shows that the dark-brown or black areas of Polistes variatns, when 

 acted upon by acids like HN0 3 , pass through a series of color changes, "deep 

 red-brown, red-brown, orange-red, orange, orange-yellow, and pale yellow," 

 and finally become colorless. If, however, the process of oxidation be 

 interrupted at any point before the transparent stage, and the material be 

 washed with water and treated with alkalis (NHjOH), color changes of 

 reverse series set in, with the end result of restoring the original color. An 

 exactly similar series of observations has been made upon decemlineata, signa- 

 ticollis, rubicunda, violescens, modesta, and other species. Treatment with 

 strong acids (HN0 3 , H,SO, HCI,) or with aqua regia result in the change 

 of the dark pigment to dark brown, then to deep reddish-brown, orange-red, 

 orange-yellow, and then to a colorless condition. Treatment with alkalis 

 before the colorless stage produces a reverse series of color changes; but I 

 have not been able to get a complete restoration of the original color, a small 

 amount having gone into solution with the dissolving of the outer portion of 

 the cuticula. If in either the progressive or regressive color changes the 

 process be stopped by washing and neutralization, any intermediate color can 

 10 T 



