456 TEXT-BOOK OF ENTOMOLOGY 



" 10. The abdominal, respiratory movements of insects are wholly reflex. Like 

 other physiologists who have examined this side of the question, Plateau finds 

 that the respiratory movements persist in a decapitated insect, as also after 

 destruction of the cerebral ganglia or resophageal connectives ; further, that in 

 insects whose nervous system is not highly concentrated (e.g. Acridiidse and 

 dragon-flies), the respiratory movements persist in the completely detached 

 abdomen ; while all external influences which promote an increased respiratory 

 activity in the uninjured animal, have precisely the same action upon insects in 

 which the anterior, nervous centres have been removed, upon the detached 

 abdomen, and even upon isolated sections of the abdomen. 



"The view formerly advocated by Faivre, that the metathoracic ganglia play 

 the part of special, respiratory centres, must be entirely abandoned. All care- 

 fully performed experiments on the nervous system of Arthropoda have shown 

 that each ganglion of the ventral chain is a motor centre, and, in insects, a 

 respiratory centre, for the somite to which it belongs. This is what Barlow calls 

 the 'self-sufficiency' of the ganglia." (Miall and Denny.) 



Plateau has made similar observations upon the respiration of spiders and 

 scorpions ; but, to his great surprise, he was unable, either by direct observation, 



FIG. 420. FIG. 421. FIG. 422. FIG. 423. 



FIG. 420. Transverse section of abdomen of a lamellicorn beetle. The position of the terga and 

 sterna after an inspiration is indicated by the thick line ; the dotted line shows their position after 

 an expiration ; and the arrow marks the direction of the expiratory movement. 



FKJ. 421. Cross-section of abdomen of cockroach. 



FIG. 422. Cross-section of abdomen of bee (Bombus). 



FIG. 423. Cross-section of abdomen of Sphinx. This and Figs. 420-122 after Plateau. 



or by the graphic method, or by projection, to discover the slightest respiratory 

 movement of the exterior of the body. This can only be explained by supposing 

 that inspiration and expiration in pulmonate Arachnida are " intrapulmonary," 

 and affect only the proper, respiratory organs. The fact is less surprising 

 because of the wide zoological separation between Arachnida and insects. 



'/ The air-sacs 



In flying insects the tracheae are in certain parts of the body 

 enlarged into sacs of various sizes. These air-sacs were first 

 observed by Swammerdam in a beetle (Geotrupes) and afterwards 

 by Sir John Hunter in the bee, Sprengel subsequently discovering 

 them in other insects. Those of the cockroach were described and 

 illustrated in a very elaborate and detailed way by Straus-Durckheim 

 (Figs. 424 and 425). These vesicles are without tsenidia. In the 

 locust (M. femur-rubrum) there is a pair of very large vesicles in the 

 prothorax (Fig. 396). The five pairs of large abdominal air-sacs 

 arise, independently of the main tracheae, directly from branches 



