294 



AKTICULATA : INSECTA. 



higher animals. On the sides of the body are breathing- 

 holes or stigmata, generally nine on each side, and these 

 open into air-tubes called tracheae, which branch through- 

 out the body, carrying air into every part, and thus aerat- 

 ing the blood in the most perfect manner, and thereby fit- 

 ting these animals for rapid and long-continued motion. 

 These air-tubes each consist of two membranes enclosing 



FIG. 3C6. 



FIG. 365. 



Pupa of Cecropia Moth cocoon removed Portion of a trachea, enlarged, a, 



showing breathing-holes or stigmata; also an the fiber which is closely wound 



antenna, and the pad-like members which in around the trachea as at e ; c, a 



the adult state expand into broad wings. branch. 



between them a spirally-coiled fiber, thereby giving them 

 great strength and flexibility. 



The muscular system of Insects consists of straight 

 fibers, more or less isolated, and not gathered into bundles 

 as in the vertebrates, but in many cases they are striated, 

 as in the latter branch. The muscles are colorless, or 

 transparent, or yellowish-white, and very soft. The mus- 

 cles are exceedingly numerous. Lyonnet found 3,993 

 muscles in a single larva, 228 of these being in the head. 

 The muscular power of Insects is enormous. It is stated 

 that the flea can leap two hundred times its own height ; 

 that beetles have been known to gnaw through lead pipes ; 



