326 ZOOLOGY 



long, and are closely applied to the outside of the alimentary 

 canal (Fig. 1 8 7). Each of them consists of a free end, which is 

 usually white, and of a brown portion which bears numerous 

 small side diverticula, giving the tubule a feathered appear- 

 ance ; they open into the small intestine. The cells lining 

 the tubule contain crystals of uric acid, which are excreted 

 through the rectum. 



The tracheal system, which carries air to every part 

 of the body, communicates with the exterior by eight pairs 

 of stigmata. The first two of these are situated close behind 

 the base of the first and second legs, between the pro- and 

 meso-, and meso- and meta-thorax respectively. The remain- 

 ing six are found on the soft integument which unites the 

 terga and sterna of the seven anterior abdominal segments. 

 Each stigma is surrounded by an oval ring of chitin, and the 

 opening can be closed by the action of certain muscles. It 

 leads into a large trachea, which in the first thoracic stigma 

 swells into a considerable vesicle ; from this two branches pass 

 off" and enter the head. The most dorsal of these unites with 

 its fellow of the opposite side, and the single trunk gives 

 branches both to the eyes and to the brain ; the other branch 

 also unites with its fellow, and supplies the antennae and 

 mouth appendages. A third branch arises from the same 

 enlargement and runs to the anterior pair of legs, and several 

 smaller branches supply muscles. Besides these, a stout branch 

 runs backward and opens into the main trachea of the second 

 stigma; this bears in its course many oval tracheal vesicles 

 (Eig. 187), and gives off branches to the elytra; two or three 

 other branches with vesicles also pass backwards, and one of 

 them supplies the second pair of legs. The main trachea from 

 the second stigma gives branches to the membranous wings, 

 the third pair of legs, and longitudinal branches which open 

 into those of the adjacent stigmata. 



The abdominal tracheae are very regularly arranged ; the 

 six stigmata on each side open into a trachea, which immedi- 

 ately divides into a dorsal and a ventral branch ; these arch 

 round, pass backward, and meet together again in the main 

 trachea of the next segment. The dorsal and ventral arches 

 of the last stigma unite to form a ring, and at the point of 



