ATMOSPHERIC RESPIRATION. 



143 



which, standing higher in the scale of creation, respire 

 the atmosphere in its gaseous form. 



427. The physiology of this class is no less diversified 

 than that of aquatic animals. Its members have a greater 

 complexity of structure, and in general, much more vivaci- 

 ty of action than the class already described. 



428. To this division belong the Insects and Amphibia, 

 as well as the Mammalia, including Man. In Insects the 

 air is respired by means of trachea, which generally per- 

 vade every part of the system, even to the wings. In the 

 Amphibia the air is swallowed, while in the Mammalia it 

 is admitted into pulmonary cavities, or lungs. 



429. Respiration in Insects. The external orifices of 

 the trachea in Insects are called spiracles, or stigmati, as 

 already explained. These are usually situated in rows on 

 each side of the body. In the larvee of many Insects 

 they are quite apparent to the eye. Fig. 91 shows these 

 organs in the form of dots 



along the sides of the larvae of 

 the honey bee. These orifices 

 lead to trachea or air tubes situ- 

 ated within the body of the In- 

 sect, and which ramify so as to 

 distribute air to all its parts. 

 On this account, these air tubes 

 have often been mistaken for 

 blood vessels. 



430. The drawing, Fig. 92, represents the magnified 

 form of a trachea and its branches, as they exist in certain 



Fig. 92. 



Fig. 91. 



What is said of the physiology of air-breathing animals ? What is the 

 diilerence in the respiration of insects and man ? What are the stigmata 

 of insects ? 



