HOW INSECTS BREATHE 451 



are seen to be granulated nuclei, with often a distinct nucleolus, each 

 sending a long, slender, transparent, pointed process along the inside 

 of the trachea. These unite to form the chitinous bands or spiral 

 threads. 



Internal hair-like bodies. In the large tracheae of Lampyris very 

 fine chitinous bristles project free into the cavity of the tube (Ger- 

 staecher), while according to Leydig there are similar chitinous points 

 in the tracheae of the Carabid beetle Procrustes. Dugardin had 

 previously (1849) called attention to such hairs, giving a list of the 

 insects in which he observed them. Emery figures a section of the 

 tracheae of Luciola, "in wendig behaart." 1 Stokes has described 

 those of Zaitha fiuminea (Fig. 414) as " internal chitinous, hair-like 

 bodies arising from the fold of the taenidia and projecting into the 

 lumen of the tubes." They are hollow, their minute cavity distinctly 

 communicating with that of the taenidium, from which they arise by 

 an enlarged base. They end in an exceedingly fine point which is 

 occasionally bifid or trifid. In Fig. 414, 4, several are shown attached 

 to the wrinkles of the tracheae near a spiracle, and at 5 is repre- 

 sented a transverse section of a trachea with three hairs projecting 

 into its cavity. 2 



Stokes has also described " certain minute, elliptical bodies in the tfenidia, 

 each with an internal, presumably glandular, appendage, to all appearance 

 forming part of the tsenidium from which it springs." These are shown in 

 Fig. 414, at l, 3, and, more in detail, at 6 ; those at 7, whose thickness is about 

 TffVff f an i ncn i appear as collections of exceedingly minute, rounded apertures 

 in a cushion-like mass. Although not commonly occurring on the tracheal 

 membrane between the taenidia, they may be found there, as at 4. 



/. The mechanism of respiration and the respiratory movements 



of insects 



By holding a locust in the hand one may observe the ordinary 

 mode of breathing in insects. During this act the portion of the 

 side of the body between the stigmata and the pleurum contracts and 

 expands ; the contraction of this region causes the spiracles to open. 

 The general movement is caused by the sternal moving much more 

 decidedly than the tergal portion of the abdomen. When the pleural 

 portion of the abdomen is forced out, the soft pleural membranous 

 region under the fore and hind wings contracts, as does the tym- 

 panum, or ear, and the membranous portions at the base of the hind 

 legs. When the tergum or dorsal portion of the abdomen falls, and 



1 Zeitschr. wissens. Zoologie, xl, 1884, Taf. xix, Fig. 8, T. 



2 Science. 1893, pp. 44-46. 



