406 



HISTOLOGY 



There are not many of these large gland-cells. They are scattered 

 singly or in groups through the membrane, and their combined secretions 

 fill the flask-shaped gland sac. A muscle fiber holds the neck and regu- 

 lates the discharge of the fluid. The secretion is a most pungent and 

 offensive fluid. It is acrid and volatile. 



The Hemiptera have in nearly all cases a pair of glands in the body 

 which open as the earwig's did on the surface. The surface, however, 

 is on the ventral side near the third pair of legs. These glands secrete 

 a fluid which, while widely different in the many species, has a peculiar 

 odor characteristic of all true bugs. In some cases it is intensely offen- 

 sive, and in others it is actually fragrant or pleasing, having a "fruity" 

 odor. The glands are of various shades of red and brown and yellow 

 and represent a distinct type. We shall examine these scent glands 

 from a large species, Belostoma Americana, in which they form two 

 symmetrical, elongated sacs or tubes. The color is a very light yellow, 

 and while the animal seldom uses them, when one is dissected and the 

 tissue is cut, the odor is intense. 



Sections show that this gland like that of the earwig is an invagi- 

 nation of the integument (Fig. 368). It is a far more involved gland, 

 being an irregularly tubular gland, convoluted in some regions. Its 

 walls are thick and lined on the outside by a very delicate connec- 

 tive tissue which holds the numerous tracheae in contact with it. 



The important 

 layers of its walls 

 are so involved 

 that it is .hard to 

 describe any one 

 without also de- 

 scribing the others. 

 The innermost is 

 a very much crum- 

 pled layer of chitin 

 continuous with 

 the exterior cuticle 

 through the neck 

 of the gland. At 

 numerous points 

 which are usually 

 situated on the 

 proximal flexures 

 of the layer, are 

 tiny openings into which the walls of the layer are produced downward 

 as a fine, clearly marked tubule of even caliber and slightly curving 



_- - d. 



FIG. 368. Bit of epithelium from the odorous gland of the Hemip- 

 ter, Belostoma. cu., cuticle; hyp.c., hypodermal cells which se- 

 crete the cuticle; sec.c., secreting cells, each with a large collecting 

 vacuole, vac.; s.s., secretion seive; d., duct to carry secretion to 

 the lumen; sec., secretion emerging from duct. One seive and its 

 duct is shown torn out and separated from the cell to which it 

 was attached. X 1275. 



