276 



HITCHCOCK'S ANATOM 



488. Trachea of Insects —Spiracles —Mechanism of 

 Respiration.— Wisdom of this Arrangement. — The res- 

 piratory vessels of Insects are analogous to those of birds 

 in that they extend through a large part of the body. 



Fig. 272. 



Trachea of "Water-Scorpion, a. Head. b. First Pair of Legs. c. First Segment of 

 Thorax, d. Second Pair of wings, e. Second Pair of Legs. /. Tracheal Trunk. g> One 

 of the Stigmatae. h. Air-Sac. 



The essential organs are Trachea or air-vessels, which open 

 upon the sides of the body, and freely communicate with one 

 another. Air sacs are found in the front parts of the body 



483. What are the essential organs of respiration in insects ? Whereabouts in the ani- 

 mal are the tracheae found ? 



