RESPIRATION OF INSECTS. 115 



to be 38, when the atmosphere was 34 ; and in sev- 

 eral instances, when the temperature of the air was 30, 

 that of the snails was considerably above 6 or 7. 



In Insects, respiration is managed differently from 

 what it is in either of the classes I have already named. 

 They have neither lungs nor gills, but are furnished with 

 minute organs, called by naturalists stigmata, which are 

 a number of small tubercules, ranged along each side 

 oi the body, each having an aperture at the top, called 

 the spiracle, through which the air enters. These stig- 

 mata are situated on the sides of the back, and lead into 

 true air-tubes, which branch off in every direction, sup- 

 plying all the parts of the body and members with air. 

 That these are respiratory organs, there can be no doubt, 

 for if they be covered up with oil, respiration ceases, 

 and the insect dies. If they be stopped up on one side 

 only, the vital functions of that side are impeded, and 

 the members are paralyzed. 



Emily. A curious kind of respiration surely ; and a 

 curious kind of circulation it must be to correspond with 

 it ; for I have not the slightest conception how it is con- 

 structed. 



Dr. B. A true circulation never has been discover- 

 ed in perfect insects. The blood is collected into one 

 large vessel situated in the back, but no vessels have been 

 observed branching off from it. The air-tubes seem to 

 serve the office of blood-vessels, and present a singular 

 contrast to those of the higher animals. In them the 

 blood is carried to the air ; in the insects, the air is car- 

 ried to the blood or as Cuvier beautifully expresses it, 

 " the air goes in search of the blood." 



The respiratory organs of some larva of insects, 

 though they live in water, are fitted for breathing 

 only air. They are situated in one extremity of the crea- 

 ture in a tail-like appendage which they always contrive 

 to keep above the surface, for if plunged entirely be- 

 neath, they appear restless and agitated, making fre- 

 quent attempts to rise again to the air. Some of them 



