WHAT AN INSECT IS LIKE: OUTSIDE 9 



in our own body. Then, there is a pair of spurs at the tip 

 of the tibia, and there is a pair of claws on the last segment 

 of the tarsus. There are often sole pads (pulvilli,) underneath 

 the tarsal segments and between the claws. 



The chitinous armor that encases the thoracic segments 

 is itself subdivided into plates, two of which may be seen 

 at the sides, and two more below on each segment, all 

 separated by thinner sutures that meet at the base of the 

 legs. 



The wings of insects are two pairs, borne always on the 

 synthorax, one pair on each segment. In the young of the 

 stonefly we may see how they arise as outgrowths from the 

 hind angles on the back. At the time of transformation 

 to the adult the wings suddenly expand to full size, and 

 acquire proper basal attachment and muscles and become 

 capable of flight. The wing when fully developed is a thin 

 sheet of membrane supported on a framework of veins or 

 nervures. It is moved by stout muscles within the thorax, 

 attached close beside its basal hinge. In flight the wing 

 is swung up and down in rapid vibration. Its front border 

 is stiffened by closely placed veins and its hind border 

 is thin and pliant. Its action, therefore, is that of sculling 

 and gliding. 



The venation of an insect wing is very complicated in the 

 details of the branching and conjoining of the veins: but 

 its general plan is simple enough, as shown in the accom- 

 panying diagram. There are three veins close together 

 and parallel near the front border, named costa, subcosta, 



