Microscopical Essays. 



241 



conducted to them through the extremities of the finer ramifica- 

 tions of the tracheal veflels : whereas M. Bonnet, in confequence 

 of a great variety of experiments, fuppofed that the infpiration 

 and exfpiration of the air was through the fpiracula, and that 

 there was no exfpiration of air through the pores of the fldta. 

 Thefe experiments were made either by plunging the caterpillars 

 into water, or anointing them with fat and greafy fubffances j 

 fome all over, others only partially. The number of fmall bub- 

 bles which are obferved to cover the fur face of their bodies, when 

 they are im merged in water, does not arife from the air which 

 is included within, and then proceeding from them, but they are 

 formed by the air which is lodged near the furface of their bodies^ 

 in the fame manner that it is about all other fubftances. To ren- 

 der the experiments more accurate, and prevent the air from 

 adhering to the {kin, before he plunged the caterpillars in water 

 he always brulhed them over with an hair pencil ; after this, very 

 few air bubbles will be found on their bodies when they are im- 

 merged in water. 



A caterpillar will remain a confiderable time under water, 

 without deftroying the principle of life ; and they alfo recover, in- 

 general, foon after they are taken out. To know whether a few 

 only of the fpiracula might not be fufficient for the purpofes of 

 refpiration, he plunged fome partially in water, fo that only two 

 or more fpiracula remained in the open air ! in thefe cafes the 

 caterpillar did not become torpid as it did when they were all 

 immerged in water. 



One caterpillar, upon which M. Bonnet made his experiments, 

 lived eight days fufpended in water, with only two of it's anterior 



G g fpiracula 



