558 W. L. TOWER, 



glandular area, which area usually becomes aggregated into two masses 

 at the inner end of the duct (PI. 20, Fig. 80). 



Concerning the character of the secretion of these glands very 

 little evidence was obtainable from a study of their histology. Many 

 show a mucin reaction, others show numerous granules of secreted 

 material, and others drops of waxy or oily material. I suspect that 

 these large glands of L. decemlineata are the cause of the peculiar 

 odor that insect possesses which renders it obnoxious to most in- 

 sectivorous animals. These glands persist in full functional activity 

 as long as the beetle lives, although the hypodermis and unicellular 

 glands will long since have degenerated. 



7) Ornamentation. The elytra of beetles are variously or- 

 namented by pigmental colors and structural effects. These I have 

 described in another paper which it is hoped will appear during the 

 present year. For the sake of completeness I shall give briefly 

 such anatomical results as were derived from that study. 



The color of the elytra of beetles is due to a pigment either in 

 the cuticula, or beneath in the hypodermis, or suspended in the haemo- 

 lymph of the central cavity of the elytron; or it may be due to 

 structural effects, — pits, striae, lamellae or scales, — or it may 

 be due to a combination of these two classes. 



The predominant colors of beetles are black, browns and yellow, 

 and these lie in the primary cuticula, as shown in the series of 

 figures (PI. 19, Figs. 57 to 62 incl.) which shows the development of 

 these colors in the primary cuticula. These colors are very stable, 

 being insoluble in water, alcohol, weak acids or alkalis, ether, essential 

 oils, etc. The colors found in the hypodermis or in the central 

 cavity are red-yellow and rarely white. These are unstable, easily 

 soluble, and fade at death or exposure to light and air. 



Structural colors are the metallic blues, greens, violets, golden and 

 most whites and in beetles are most commonly produced by lamellae. 



Scales are of common occurrence in beetles and are varied in 

 their form, size and the color effect produced. They have been well 

 studied by Dimmock (1883) as adult structures. In development the 

 scales of Coleoptera follow exactly the same course as was found 

 by Mayer (1896) in the Lepidoptera and there can be no doubt 

 as to the complete homology between the scales and the colors 

 produced by them in these two orders. In several Cerambycidae an 

 interesting condition was found in the close association of a gland 

 with those scales which are destined to become dark in color (PI. 20, 



