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 

 \y easily deprived of 

 breath and killed. 



k * In some aquatic 

 larva 1 such as those 

 of D>/tfcid\ J^fiKta/ifi i 

 Fig. 49. (Fjo-. 51, pupa), and 



, and also in some perfect insects, 

 as in Nepa and ltn<itr<i, the parts sup- 

 porting the stigmata are prolonged into slen- Fig. r.o. 



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

 breathes the atmospheric air. 



Affi-ioii (Fig. .">:>) affords a good instance of branchia 1 

 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 trachea! ves- 

 sels, with which they are abun- 

 dantly supplied, and which ter- 

 Fig. si. minate in single trunks, into the 



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

 as in insects which live in the open atmosphere." 

 (Newport.) 



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

 the larvae and pupa 1 of Gnats, consist of slender fila- 

 ments arranged in tufts arising from a single stem. Fi ^- '-' 

 In the larva of Gi/rhius and the aquatic caterpillar of a moth, 



I 



I 

 I 

 I 



FIG. 49. Chamber leading- into the trachea; a, a, external valve protecting the 

 outer opening of the stigma, or breathing hole; b, e, c, inner ami more complicated 

 valve closing the entrance into the trachea (I, /j); ;, conical occlusor muscle 

 closing the inner orifice. Front Strniix Dirrckhe-im. 



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

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

 traclieal branch. From Strnitx Dtircfcliciin. 



FIG. 52. One of the three gill-like appendages to the abdomen of the larva and 



pupa of Ayrion enlarged, consisting of a broad leaf-like expansion, permeated by 



trachea: which take up by endosmosi.s the air contained in water. O 



4* 



