144 



TJic Pupa of Cliii'ojwmus 



The castinj 

 of the 

 tracheal 

 mil. 



The brandies of the longitudinal tracheae which pass 

 to the tracheal gill take origin near together, and are at 

 first tortuous and crowded. They soon break up, nearly 

 at the same level, into a multitude of much smaller tubes, 

 which run parallel to one another up to and through the 

 stem of the gill, and then break dichotomouslv into still 



Fig. no. — Termiiiatinn of filament of tracheal gill of pnpa. with 

 tracheae euclosed. 



liner branches, which pass along the tubules of the gill. 

 Beyond the common stem the tracheae branch with the 

 containine: tubules until the ultimate tubules are reached; 



Fig. hi.— Sagittal section of ptipa, passing through base of tracheal 

 gill and mesothoracic spiracle, ps, pupal skin, sp, mesothoracio 

 spiracle of fly. tr, large trachea, cs, chitinous septa at base of tracheal 

 gill, tg, tracheal gill. 



the tracheae then branch independently, so that one 

 tubule may contain several tracheal branches. 



Within the stem of the gill the tracheae are supported 

 bj' chitinous septa, which are easily distinguished in 

 sections by their solidity and well-marked colouration. 



