124 THE PHILOSOPHY 



tures refpire. Each gill confifts of a ftiort trunk, and two large 

 branches, or tubes, which give off on all fides a number of fmaller 

 ramifications, and are perfedtly fimilar to the tracheae of other in- 

 fers. At the origin of every gill, two tracheae penetrate the trunk, 

 and are difperfed through the body of the animal. 



Though the ftigmata, or refpiratory organs, of caterpillars and 

 other infeds, were long known to ferve the purpofe of infpiration, 

 yet it was uncertain whether the animals refpired by the fame ori- 

 fices, till Bonnet, and, after him, Reaumur, afcertained the fad by 

 many curious and accurate experiments. The firft of thefe authors 

 immerfed numbers of caterpillars, of different kinds, and at different 

 times, in water, and he obferved, both with the naked eye, and by 

 the afTiftance of a glafs, bubbles of air iffuing from various parts of 

 their bodies, and particularly from the ftigmata. To remove all de- 

 ception from his experiments, before immerfion, he carefully moif- 

 tened the caterpillars with water, in order to diflodge any portions 

 of the external air that might be adhering to their bodies. Some 

 of them he allowed to remain fo long under water, that they had 

 every appearance of death. He then raifed the head and the two 

 anterior ftigmata above the furface. The head, and firft pair of 

 legs, foon began to move from fide to fide ; and the body neceflari- 

 Jy partook of the fame motions. During thefe movements, many 

 bubbles of air iflued from the pofterior and intermediate ftigmata, 

 which ftill remained under water; but the membranous limbs con- 

 tinued nearly at reft. He next kept a caterpillar under water till all 

 motion was fufpended. Then he elevated the anus and the two lafl: 

 ftigmata above the furface, that they might have a communication 

 with the external air. He kept the animal in this fituation about 

 half an hour, without any fymptoms of re-animation. After raifing 

 the body fuccefllvely from the laft to the firft pair of ftigmata, ftill 

 the animal exhibited no fymptoms of life; but, when he expofed 



the 



