148 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. 



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 present 

 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. 



In the winged Insects, every part is furnished with air 

 tubes, which ramify in all directions, and which circulate 

 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. 



In the vertebrated terrestrial animals, the organs into 

 which the air is admitted for the purpose of respiration, 

 are called lungs ; the tube leading to which is called 

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

 per 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 stom- 

 ach, 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 w r ay 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 re- 

 spiration. 



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 7 What is the epiglottis, and what its 

 use'? 



