180 ANATOMY. 



organs. Thus, therefore, the air bladders of the abdomen form a com- 

 pact net-Avork, which is, as it were, spread out between the spiracles 

 and the horny arches. If the abdomen be drawn together by muscular 

 contraction the horny arches rise, extend the tracheae longitudinally, 

 and consequently the air contained within them is forced out ; but 

 upon its expansion the air again streams in, when every bladder, 

 through the elasticity of its filament, is again shortened and dis- 

 tended. The respiratory system of Truxalis nasutus, of which 

 Marcel de Serres has given a figure *, is still more complicated, 

 for in it the bladders do not originate immediately from the 

 spiracles, but, by means of long tubes, from the common tubular 

 vessels which connect all the spiracles, and at the opposite end unite 

 in a second but more delicate longitudinal tube. Also the two oppo- 

 site bladders are held in connection together by undivided tolerably 

 narrow tubes. In the abdomen there are twenty bladders, ten on 

 each side ; in the thorax six larger ones, four in the meso- and meta- 

 thorax, one very large pear-shaped one above, at the dorsal portion of 

 the pro-thorax, close to the crop, and besides many vesicular disten- 

 sions of the arterial vessels ; in the head there are six large bladders, 

 two laterally, contiguous to the muscles of the mandibles, two above, at 

 the vertex over the eyes, two in the forehead before the eyes, and 

 between these several smaller vesicles. 



The second chief form of the vesicular air vessels is found among the 

 Coleoptera in the family of the Lamellicornia, among the Lepidoptera 

 in the Crepuscularia, particularly in the males, and then in the 

 dragon flies. 



In the Lamellicornia the chief distribution of the air vessels, as 

 throughout the Coleoptera, is arterial, for fascicles of air vessels ori- 

 ginate from each spiracle; but each finer branch distends, prior to its 

 ultimate and finest ramification, into an oval bladder, which is of a 

 more delicate structure than the rest of the branch, whence Marcel 

 de Serres and Straus deny the presence of the spiral fibre in these 

 vessels, which Suckow maintains to be the case. It is true that these 

 bladders are more transparent than the tubes, but they exhibit a 

 peculiar punctured structure, as was even perceived and figured by 

 Swammerdam f, and also by Sprengel J ; and thence I would assume 



* As above, PI. XV. ; i 

 t Biblia Nature, PI. XXIX. f. 10. J Commentar., PI. I. f. 1113, 



