Fig. 82.—Tracheal System of Cockroach. The ventral integument and viscera removed to show the dorsal tracheal communications. × 5.
Fig. 83.—Tracheal tube with its epithelium and spiral thread. Slightly altered from a figure given by Chun (Rectal-drüsen bei den Insekten, pl. iv., fig. 1).
Tracheal Tubes.
The accompanying figures sufficiently explain the chief features of the tracheal system of the Cockroach, so far as it can be explored by simple dissection. Leaving them to tell their own tale, we shall pass on to the minute structure of the air-tubes, the spiracles, and the physiology of Insect respiration.
The tracheal wall is a folding-in of the integument, and agrees with it in general structure. Its inner lining, the intima, is chitinous, and continuous with the outer cuticle. It is secreted by an epithelium of nucleated, chitinogenous cells, and outside this is a thin and homogeneous basement membrane. The integument, the tracheal wall, and the inner layers of nearly the whole alimentary canal are continuous and equivalent structures. The lining of the larger tracheal tubes at least is shed at every moult, like that of the stomodæum and proctodæum.