240 



Microscopical Essays. 



On the Respiration of Insects. 



As refpiration is one of the moft important actions in the life of 

 every animal, great pains have been taken by many naturalifts to 

 inveftigate the nature of this aclion in infects • to prove it's exig- 

 ence, and explain in what manner it is carried on. Malphigi, 

 Swammerdam, Reaumur, and Lyonet, have difcovered in the 

 caterpillar two air-veffels placed the whole length of the infect, 

 thefe they have called the tracheae ; they have alfo (hewn that an 

 infinite number of ramifications proceed from thefe, and are dif- 

 perfed through the whole body ; that the tracheal veffels communi- 

 cate with particular openings on the fkin of the caterpillar, 

 •termed fpiracula ; there are nine of thefe on each fide of the 

 body. Thefe veffels feem calculated for the reception of air ; 

 they contain no fluids, are of a cartilaginous nature, and when 

 -cut preferve their figure, and exhibit a well-terminated opening. 

 Notwithftanding this difcovery, the exiftence of refpiration has 

 not been proved in many fpecies of infects, and the mechanifm 

 thereof is very obfcure in all 4 and it is no more furprizing, that 

 refpiration does not exift in the embryo ftate of infecls, than in 

 that of other animals, where we find that refpiration, which after 

 their birth is abfolutely neceflary for their exiftence, to be by no 

 means fo before k. 



M. de Reaumur thought that the air entered by the fpiracula 

 into the trachea, but did not come out by the fame orifice, and 

 confequently that the refpiration of infecls was carried on in a 

 manner totally different from that of other animals, that the air 

 was exfpired through a number of fmall holes, or pores, w 7 hich 

 are to be found in the Ikin of the caterpillar, after having been 



conducted 



