BRUES: PARASITIC HYMENOPTEKA. 5 



compound microscope with two-thirds objective and two inch eye- 

 piece. 



Since many of the details are indicated by color rather than surface 

 structure, it is necessary to examine both by obliquely reflected light 

 and bv as nearly vertical illumination as possible. The latter can be 

 obtained either by using an objective furnished with a prism for vertical 

 illumination, or by placing on the stage of the microscope around the 

 specimen, the rim of a deep pillbox from which the bottom has been 

 removed. This simple device shuts off all very oblique light and 

 renders visible wing venation and other characters which are otherwise 

 often very difficult to make out. 



One of the most remarkable facts connected with the preservation of 

 the Florissant insects is the apparent fidelity with which colors are 

 usually preserved or indicated. It is not so difficult to understand 

 the preservation of metallic colors which are dependent upon physical 

 structure, but the distinction between red, black, and yellow is usually 

 also retained as well as the difference between hyaline and infuscated 

 wings. This is proven beyond all doubt by the similar color of 

 different specimens belonging to the same species, and the general 

 color tendencies of fossil species as compared . with those of recent 

 related forms. In a small proportion of the specimens carbonization 

 has proceeded to the point of blackening the entire specimen but this 

 is unusual. There is probably no doubt that a part of the color differ- 

 entiation both in recent and fossil insects of these groups is dependent 

 upon the thickness of the chitin covering the different parts of the 

 body, and it is much easier to see how this may have been preserved 

 than to understand the retention of actual pigment colors or their 

 proper representation. The peculiar method of entombment of these 

 fossils must be, I think, in great part responsible for this. The vol- 

 canic ash of which the matrix was formed, was evidently very fine, 

 and its similarity to cement rock has led me to believe that the rapidity 

 with which it originally hardened must have been very great. This 

 would account in great measure for the failure of the chitin to macerate 

 as it will do in the presence of much water, and perhaps also for the 

 presence of pigment. In his Tertiary Insects ('90, p. 24) Scudder 

 quotes Dr. M. E. "Wadsworth who examined specimens of these insect- 

 bearing shales, to the effect that they probably originated from a moya, 

 or mudflow which was rapidly deposited in the shallow waters of the 

 Florissant lake without any preliminary erosion. That the deposition 

 and hardening of the shales was unusually rapid seems to me un- 

 doubted, for in no other way can I account for the presence of 



