10. The abdominal respiratory movements of Insects are wholly reflex. Like other physiologists who have examined this side of the question, the writer finds that the respiratory movements persist in a decapitated Insect, as also after destruction of the cerebral ganglia or œsophageal connectives; further, that in Insects whose nervous system is not highly concentrated (_e.g._, Acridiidæ 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 carefully 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. * * * * * The writer has made similar observations upon the respiration of Spiders and Scorpions;[156] but to his great surprise he has been unable either by direct observation, 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 intra-pulmonary, and affect only the proper respiratory organs. The fact is less surprising because of the wide zoological separation between Arachnida and Insects. [156] De l’absence de mouvements respiratoires perceptibles chez les Arachnides (Archives de Biologie de Van Beneden et Van Bambeke, 1885.) _Respiratory Activity of Insects._ The respiratory activity of Insects varies greatly. Warmth, feeding, and movement are found to increase the frequency of their respirations, and also the quantity of carbonic acid exhaled. In Liebe’s[157] experiments a Carabus produced ·24 mgr. of carbonic acid per hour in September, but only ·09 mgr. per hour in December. A rise of temperature raised the product temporarily to twice its previous amount; but when the same insect was kept under experiment for several days without food, the amount fell in spite of its increased warmth. Treviranus[158] gives the carbonic acid exhaled by a Humble-bee as varying from 22 to 174, according as the temperature varied from 56° to 74° F. [157] Ueb. d. Respiration der Tracheaten. Chemnitz (1872). [158] See table in Burmeister’s “Manual,” Eng. trans. p. 398.