ATMOSPHERIC RESPIRATION. 



147 



which, standing higher in the scale of creation, respire 

 the atmosphere in its gaseous form. 



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 vivacity of action than the class already described. 



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 

 pervade every part of the system, even to the wings. 

 In the Amphibia the air is swallowed, while in the Mam- 

 malia, it is admitted into pulmonary cavities or lungs. 



Respiration in Insects. The external orifices of the 

 trachea in Insects are called spiracles or stigmata, as 

 already explained. These are usually situated in rows 

 on each side of the body. In the Iarva3 of many Insects 

 they are quite apparent to the eye. Fig. 81 shows 

 these organs in the form of 

 dots along the side of the larva, 

 of the honey bee. These ori- 

 fices lead to trachea or air 

 tubes situated within the body 

 of the Insect, and which rami- 

 fy so as to distribute air to all 

 its parts. On this account, 

 these air tubes have often been 

 mistaken for blood vessels. 



The drawing, Fig. 92, represents the magnified form 

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



Fig. 92. 



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

 the difference in the respiration of insects aud man 7 What are the 

 stigmata of insects 1 



