ORGANS OF RESPIRATION. 



41 



serous, and an internal mucous membrane, inclosing between 

 them a spirally convoluted fibre, thus giving great strength 

 and flexibility to the tube." 



Nearly all the air enters through the thoracic and first 

 abdominal spiracles, so that on pinching most insects on 

 the thorax they can be 

 \^ easily- deprived of 

 breath and killed. 



''In some aquatic 

 larvffi such as those 

 of Dyticidw, En'stalis 

 (Fig. 51, pupa), and 

 Ephydra, and also in some perfect insects, 

 as in Nepa and Ranatra, the parts sup- 

 porting the stigmata are prolonged into slen- 

 der tubes, through which the insect, on rising to the surface, 

 breathes the atmospheric air. 



Aqrion (Fig. 52) affords a good instance of branchi;e 

 or gill-like expansions of the crust, or skin. It is 

 supposed that these false gills, or branchia^, "absorb 

 the air from the water, and convey it by the minute 

 ramifications of the tracheal ves- 

 sels, with which they are abun- 

 dantly supplied, and which ter- 

 minate in single trunks, into the 

 main trachea?, to be distributed over the whole body, 

 as in insects which live in the oi)en atmosphere." 

 (Newport.) 



Of branchiffi there are three kinds. The first, as in 

 the larvffi and pup* of Gnats, consist of slender fila- 

 ments arranged in tufts arising from a single stem. 

 In the larva of Gyrhms and the aquatic caterpillar of a moth. 



Fig. 4!>. Chamber leading into tlie trachea; n, a, external valve protecting the 

 enter opening of the stigma, or breathing hole; b, c, c, inner and more complicated 

 valve closing the entrance into the trachea (I, k); m, conical ocdusor muscle 

 closing the inner orifice.— From Straus Ihirckheim. 



Fi<i. 50. Portion of a trachea divested of its peritoneal envelope, o, spirally 

 convoluted fibre, closely wound around the trachea, as at e ; c, origin of a secondary 

 tracheal bran<-h.— From Sfrnvs Ihirrhhcim. 



Fig rr2. One of the throe gill-like apiK-ndages to the abdomen of the larva ami 

 pupa of J>/rion enlarged, consisting of a broad loaf-like expansion, permeated by 

 trachese which take up by endosmosis the air contained in water.— OrUjimd. 



r. Crl. 



