160 THE LIFE OF AN INSECT. 



caterpillars and maggots, to use the customary 

 terms for these varieties of Iarva3, were confined 

 in vessels containing only about eleven cubic 

 inches of atmospheric air, and so stopped as to 

 preclude the ingress of any fresh air whatever, 

 although furnished with an abundant supply of 

 food, they soon died. When he put them into a 

 still smaller vessel, they died the sooner. In fact, 

 precisely in proportion to the purity, or to the 

 amount of the air contained in the space in which 

 he confined them, were their lives prolonged or 

 shortened. He found on examining the air that 

 it contained, as above stated, carbonic acid gas. 



We may, therefore, consider the question as 

 settled that larvae do breathe. Strange it may 

 appear to some, but neither in the larva nor in any 

 other form of its existence do insects breathe by 

 the mouth. How, then, it may be asked ? We 

 shall now describe their breathing apparatus very 

 briefly. Along each side of the body runs a deli- 

 cate tube for the conveyance of air, called a 

 trachea, or when both are spoken of, the tracheae ; 

 these channels run underneath the muscles and 

 skin, and open to the air by little branch tubes, 

 the mouths of which are called spiracles. Besides 



