144 VITAL FUNCTIONS. 



Insects. The cup-like appendage situated on the upper 

 and central part of the trunk, is the stigmata, opening 

 from the atmosphere to the trachea. There are, as above 

 shown, about ten of these orifices on each side of the larva 

 or caterpillar of most Insects. 



431. These stigmata are always open and full of air, 

 and if an Insect be immersed in water, minute bubbles of 

 air may be seen escaping from each, being excluded by 

 the fluid. While under the water, the trachea often pre- 

 sent a silvery appearance, from the air they contain. If 

 all the air is expelled, and the vessels are filled with 

 water, the Insect is drowned ; and if the stigmata be 

 closed by oil or any other substance, so as to prevent the 

 ingress of air, the Insect will be suffocated 



432. In the winged Insects, every part is furnished with 

 air tubes, which ramify in all directions, and which circu- 

 late air as the arteries do blood. The nervures, which 

 have the appearance of veins on the wings of Butterflies 

 and other Insects, are a part of the organs of respiration. 



RESPIRATION IN REPTILES. 



433. In the vertebrated terrestrial animals, the organs 

 into which the air is admitted for the purpose of respira- 

 tion, are called lungs : the tube leading to which is 

 called trachea, or wind-pipe. The trachea divides at the 

 upper part of the chest into two tubes, leading to each 

 lung, and these are called bronchia. The upper end of 

 the trachea, which lies before the passage to the stomach, 

 called the esophagus, is carefully guarded by a valve 

 called the epiglottis, from the intrusion of any substance 

 about to be swallowed, or passed into it, on its way to 

 the stomach. The action of swallowing closes the epi- 

 glottis very accurately over the passage to the wind 

 pipe, which is again instantly opened in the act of respi 

 ration. 



434. This description applies to air-breathing animals, 

 with back bones generally ; but when we come to examine 



What are the lungs? What is the tube called which leads to the lungs 

 What are the bronchia ? What is the epiglottis, and what its use ? 



