BREATHING OF INSECTS. 



349 



Yonder sleeping flock and those shade-seek- 

 ing cattle are not less debtors to the air for life 

 than is the cowherd on the river bank, or the 

 shepherd under the elm. And in the animals 

 the function of breathing differs but little from 

 the same function as carried on in the human 

 frame. In the animal world generally there is 

 found the same general principle to prevail with 

 respect to this function ; that is, the air is 

 drawn into a cavity upon the sides of which the 

 vessels containing the blood ramify, and so the 

 vital oxygen of the air becomes applied to the 

 blood and is re- 

 ceived into it, and 

 so also the impuri- 

 ties and waste mat- 

 ters of the system, 

 those at least which 

 can be thrown off 

 as gas or vapour, 

 become discharged. 

 There is a remark- 

 able exception in 

 the structure of in- 

 sects. Here there 

 is no organ like our 

 lungs : but, strange 



. . AIB-TUBES OF INSECTS. 



to say, the air is 



conveyed by a series of beautiful fine pipes 



all through the body, even to the extremities 



