NO. 2 RECOGNITION AMONG INSECTS — McINDOO 39 



fluid ; this gland is simple and is composed of one reservoir whose 

 neck opens into a simple tube. 



Hoffbauer (1892) who has made a special study of these glands 

 in the elytra and pronotum of beetles, thinks that their secretion 

 is probably for protection and he divides them into simple and com- 

 pound glands. A compound gland is nothing more than a collection 

 of the unicellular simple glands. The efferent canal may be either 

 narrow, flaskshaped, or champagne-corklike, and it may or may not 

 come to the surface at the base of a hair. Each gland cell may or may 

 not possess a small reservoir. 



Cuenot (1896b) asserts that when the beetles, Melasoma populi 

 and M. tremulco, are irritated an odorous and opaline liquid may be 

 seen on the elytra. This Hquid is secreted by unicellular glands 

 grouped in rosettes around a common efferent canal. These glands 

 are found in the thickened portion of the elytron at the basal end. 

 He regards the liquid secreted as an important means of defense. 



Tower (1903) found simple and compound glands in beetles vary- 

 ing a great deal in complexity. 



The simplest glands are single hj'podermal cells modified for a glandular 

 function, and are uniformly distributed over the entire bodj' surface. In the 

 elytron they arise in the pupal stage by the direct modification of one of the 

 hypodermal cells of the wing lamella. 



Instead of a gland opening at the bottom of a pit, it often opens 

 at the top of a cone or stalk situated in a pit. In regard to the com- 

 pound glands he says : 



I suspect that these large glands of Leptinotarsa dccemlineata are the 

 cause of the peculiar odor that insect possesses which renders it obnoxious 

 to most insectivorous 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. 



Casper (1913) found hypodermal glands widely distributed over 

 the entire body surface and legs of Dytiscus margmalis, and Lehr 

 ( 1914), who resumed the search for hypodermal glands in other parts 

 of the same insect, found them widely distributed in the wings and 

 elytra. 



The present writer (1916b) found unicellular glands widely dis- 

 tributed over the thorax, abdomen, legs, and elytra of the coccinellid 

 beetle, Epilachna horealis. The wings contain none of these glands 

 and the head with its appendages were not examined. Each gland 

 cell Hes beneath a pore in the chitin, and each pore possesses a spheri- 

 cal reservoir, from which runs an efferent canal to the exterior. 



