70 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. 



St- 



walls, traversed by numerous septa and folds which bear an extremely 



rich network of capillaries. The air tubes or tracheae (fig. 65) consti- 

 tute a branched system of canals 

 which extend throughout the 

 whole body, and carry the air 

 to all the organs. Thus instead 

 of the respi- 

 ratory pro- 

 cess being 

 localised, as 

 it is in ani- 

 mals with 

 lungs, it is 

 carried on in 

 all tissues 

 and organs 

 of the body, 

 which are 

 surrounded 

 by a fine 



tracheal network. Nevertheless, the air tubes 



in the case of the modification known as fan- 



tracheae present an approximation in their 



structures to lungs, in that the main stems, 



without further branching, give rise to flat 



hollow leaves. 



FIG. 6). Tracheje with fine branches 

 (after Leydig). Z, cellular outer wall ; 

 Sp, spiral thread. 



FIG. GG6. Lateral view of head and body of an 

 Acridium. St, stdgmata ; T, Tympanum. 



Openings in the body wall are present, placing 

 the organs of aerial respiration in communica- 

 tion with the exterior. These openings may 

 be numerous, and paired, placed symmetrically on the sides 



FIG. GGa. TracLeal sye 

 tern of a Dipterous 

 larva. Tr, Longitudi- 

 nal stem of the right 

 side with tufts of tra- 

 cheae; St.', and St", 

 anterior and posterior 

 stigmata ; Mh, oral 

 hooks. 



