ORGANS OF RESPIRATION. 



533 



which, by anastomosis, establish a free communication with the 

 adjoining stigmata of the same side ; there are also several 

 transverse anastomosing branches, (144. h. I.) which unite 

 below (144. k.) with those of the opposite side, to form a free 

 communication between the two sides of the body ; and there 

 are numerous other branches (\44.f.g.) from the same trachea! 



FIG. 144. 



origins, which ramify directly on the various organs of the 

 body. 



Sometimes, as in blatta and locust a, the longitudinal 

 branches form but one dorsal and one ventral median trunk, 

 from which branches are distributed to the organs, and be- 

 tween which a free communication is established by regular 

 transverse anastomosing branches. The longitudinal lateral 

 trunks are often much dilated in aquatic insects, to render them 

 buoyant, and to provide for their interrupted respiration ; 

 and the aquatic larvae of several insects, as of libellula, 

 inspire air solely from water regularly introduced and ex- 

 pelled through the anus, as holothuriae inspire water for res- 

 piration by the same orifice. In the rectum or cloaca of 

 these larvae, indeed, there are several compact rows of trian- 

 gular branchial lamellae, which line its whole parietes, and 

 which support the capillary extremities of the abdominal tra- 

 cheae ; some have as many as eighty of these plates, dis- 

 posed symmetrically in rows of pairs within the rectum. 

 Besides the minute cells, (144. d. e. f. g.) in which, as in the 

 lungs of vertebrata, the tracheal ramifications of the higher 

 insects frequently terminate, there are often more consider- 

 able vesicular dilatations on the great lateral longitudinal 



