INSECTA, A CLASS OF ARTHROPODS 197 



by many veins and, when not in use, are folded lengthwise, like a 

 fan, beneath the narrower anterior wings. 



Abdomen 



The abdomen consists of ten movable segments, each composed 

 of an upper and lower part, united by a membrane which allows 

 it to expand and contract in the process of breathing. There 

 are no jointed appendages as on the head and thorax, but eight 

 of the segments have breathing pores (spiracles) on each side. 

 The segment next to the thorax bears the ears which are large 

 membrane-covered cavities on either side. 



The extreme posterior segments in the female bear two pairs of 

 hard and sharp-pointed organs called ovipositors (egg placers) 

 whose function is to dig a hole in the ground in which the eggs are 

 laid. The males have no such organs but the posterior of the ab- 

 domen is enlarged and rounded upward. 



Active Life. The activity of insects is well known but little ap- 

 preciated. They have the most enduring and powerful muscles 

 of any animal, in proportion to their size. Think of the long swift 

 flight of bees, often extending for miles, at enormous speed; think 

 of the loads carried by ants and beetles; of the hard labor done by 

 boring and burrowing insects, then compare their size and 

 weight with our own and see how fast we ought to fly or run, how 

 far we should jump, or how much we should carry, if we had their 

 muscular ability. Of course their enormous activity requires a 

 great deal of energy which means that they must use a large amount 

 of food, and this, in turn, implies a complete digestive apparatus. 

 The digested food requires oxygen to oxidize it and liberate its 

 energy and this requires a perfect system for breathing to supply 

 the oxygen. To control such a powerful high-speed engine, a well- 

 developed nervous system is also demanded. 



The foregoing sounds like the " House that Jack Built " but is 

 an outline of just what we find to be the case, not only in insects 

 but in all higher forms. It is merely another instance of our order 

 of study, " Structure, Function, Adaptation." 



