26 ILLINOIS BIOLOGICAL MONOGRAPHS [420 



wings beneath, which come between the elytron and a part of the pig- 

 mented abdomen, give no opportunity for accurate observations with 

 the elytra in position except as one slips pieces of paper under them, 

 which may injure the elytra so as to give abnormal development. The 

 elytra must be removed and mounted in glycerine jelly, or cleared in 

 balsam. It is necessary to hold the slide in position over the surface 

 of a good glass plate that has been painted white on the lower surface 

 and not magnify tliem or if so, only about two diameters with a reading 

 glass. The fresh, unmounted elytra may be placed in formalin in a 

 watch glass painted a neutral gray or yellowish tone which is the same 

 color as that presented by the elytron before pigmentation when viewed 

 in transmitted light. By this method and with individuals killed at 

 different stages, and with the use of a Zeiss binocular microscope, I 

 have been able to follow the course of pigmentation of the elytra. The 

 elytra have been examined in cross section ; there are no thickenings in 

 the primary cuticula in which all the pigment is located, except the 

 small thickenings that have been described as occurring in the area 

 immediately in front of hairs, and these have been carefully considered 

 and their relative number as effecting the color effect practically elim- 

 inated. The cuticula is somewhat thinner at the tip of the elytron. The 

 actual hairs present are surrounded by an area that is fully pigmented, 

 but this also has been taken into account. Elytra of C. repanda show 

 beginnings of pigmentation which often are strongest near the costal 

 border at the end of 4 to 5 hours (Fig. 111). The chief of the areas 

 showing lack of pigment are in the lines A and B and are particularly 

 prominent near the base. Later (Figs. 112 and 113) these lines are 

 broken into spots which correspond to spots found in certain Eurasian 

 and African species (Figs. 147 to 187, PL XII, and 241 to 280, Plate 

 XIV) . The series of stages that I have had has been small and not suited 

 to the detailed comparison as some of the following species are, but shows 

 the same thing. 



The color development in C. lecontei Hald. begins very faintly 

 apparently at about the posterior end of the anterior third of the elytron 

 at first the permanent markings are difficult to distinguish, but a little 

 later they become distinct patches. Two ontogenetic markings between 

 the base of the elytron and the general arrangement of pigment at the 

 end of 4 to 5 hours (Fig. 114) correspond very closely to conditions 

 found in repanda. Longitudinal, heavily pigmented stripes that stand 

 out in some individuals, lie in the lines of the tracheae and hairs, and 

 become more pronounced as the development continues. Figure 115, 

 12 hours after emergence, shows none of the spots characteristic of the 

 others shown but has indications of a cross band which never occurs in 

 lecontei but which is present in rugifrons and modesta of the Atlantic 



