INSECTS 



229 



Spiracle with its trachea} removed from an 

 insect; s, spiracle. Three times natural 

 size. Photographed by Davison. 



Tracheae.— The trachese divide and subdivide like branches of 

 a tree so that all the body cavity is reached by their fine endings. 

 Some even pass outward into the 

 veins of the wings. Each of 

 these tubes contains air. The 

 blood of an insect does not cir- 

 culate through a system of closed 

 blood tubes as in man, but in- 

 stead it more or less completely 

 fills that part of the body cavity 

 which is not filled with other 

 organs. A heart (a hollow mus- 

 cular organ containing several 

 openings, situated on the dorsal 

 side of the insect) causes move- 

 ment of the blood inside the body 

 cavity in much the same way 

 that a rubber bulb would circu- 

 late water if squeezed inside a 

 pail of water, so that sooner or later the blood comes in contact 

 with the oxygen passed in through the trachese. 



Muscular activity. — Insects have the most powerful muscles of 

 any animals of their size. Relatively, an enormous amount of 

 energy is released during the jumping or flying of a grasshopper. 

 The tracheae pass directly into the muscles, where oxidation takes 

 place when the muscles are exercised. Thus oxygen is taken 

 directly to the parts of the body where it is to be used. The body 

 temperature of the grasshopper is slightly higher than the sur- 

 rounding air. Why? 



Mouth Parts. — Feed a grasshopper with a blade of grass. Note how the 

 animal holds the grass. What appendages aro used ? Note the upper lip and 

 lower lips, the latter biparted. The dark brown Jaws (mandibles) may be 

 seen underneath. Below them are a pair of smaller pointed parts, the 

 maxillse, to which are attached a pair of jointed palps. Note also that palps 

 are attached to the lower lip. 



Food Taking and Blood Making. — The plant food taken by the 

 grasshopper is held in place in the mouth by means of the little 

 jaws or maxillse while it is cut into small pieces by the mandibles. 



