46 ILLIXOIS BIOLOGICAL MONOGRAPHS [440 



The same is true of Texas specimens. Specimens from E. Tennessee 

 are reduced as in figure 523 and those from eastern Kansas are usually 

 immaculate with a few like 523. 



C. punctul<ita representing the Mexican group, has been studied 

 and while widely distributed fails to show pattern varieties and did not 

 show any modification when subjected to 40°C in the experiments. It 

 also shows no geographic variation in markings. C. lemniscata shows 

 the vitta broken in about seventeen out of seven hundred and fifty 

 individuals. These patterns are like liitcolineata (Fig. 24, PL III). 

 C. carthagena, hacmorrhagica and C. gahbi of San Diego, California, 

 show a tendency for the markings to disappear by the spreading of 

 pigment over the areas of the markings. 



COLORS OP TIGER BEETLES 



CAUSES OF COLORS 



The pigment present in the cuticula of Cicindela is essentially all 

 in the primary cuticula (Fig. 1). This pigment has been demonstrated 

 by Gortner to be melanin and not the compounds stated by Tower 

 (1906). This pigment is, in all the elytra observed, either brown or 

 black. It is the result of the oxidation of tyrosin or related compound 

 by tyrosinase (Riddle, 1909). In the case of all elytra examined in 

 transmitted light which covers nearly two hundred species no color but 

 dark brown ranging to black has been observed, no matter what bril- 

 liant spectrum colors were present in the elytra as view in reflected light. 



Professor Michelson has made a study of the causes of the bright 

 metallic and spectrum colors in various insects and feathers and has 

 found that the colors are due to very thin surface films, metallic in 

 character. He has very kindly examined elytra of several species, in- 

 cluding Cicindeki chinensis Dej., severaF varieties of C. limbalis, and 

 several color varieties of C. scutellaris. The colors of the first two 

 differ in different parts of the same elytron, the second named species 

 showing blue and red and differing sometimes in the same population 

 from black to green or blue, red, etc. The first two species gave results 

 too indefinite to report. The third species, C. scutellaris, occurs on the 

 Atlantic coast as a brilliant green form with some dead black forms 

 among them in the same population ; and in Kansas and Oklahoma the 

 population is a flame red. The red scutellaris from Kansas showed a 

 "preponderance of red in the spectrum, negative phase change at red 

 end of spectrum, and positive phase change at blue end. The green, 

 east-coast forms showed excess of blue-green with positive phase change 

 at red end and negative phase change at blue end." The black form 

 which occurs as a part of the general population with the green is 



