26 The Form of Insects 



ments flat on the ground have the under-surface 

 of these segments broadened to afford support, and 

 provided with special cushion-like thickenings of the 

 skin or beset with glandular hairs secreting an ad- 

 hesive fluid. Such hairs are specially present on 

 the pad (^puhillus) which is to be seen between the 

 bases of the claws in most insects. This pad has 

 been regarded as a sixth segment to the foot (fig. 9^). 

 In flies and bees it forms a delicate membrane which, 

 owing to the presence of the adhesive hairs, sticks 

 closely to a smooth surface ; it is by the action of 

 these foot-pads, for example, that a fly is able to 

 walk up a window-pane. But when the insect is 

 passing over a rough object, the pad can be raised 

 so as to escape injury, the claws then affording a 

 secure foothold (2, lo). 



Careful observation and photography have shown 

 that an insect, in walking or running, moves its legs 

 in two sets of three, so that at each step it is 

 supported on a tripod, formed of the first and third 

 legs of one side with the second of the other. One 

 tripod thus affords a firm base of support while the 

 other three legs are being moved forward to their 

 new position (ll, 12). 



Wing's. — A pair of wings is carried on the second 

 segment (mesothorax) and another on the third seg- 

 ment (metathorax) of the fore-body. The narrow 

 attachment of a wing to its thoracic segment is called 

 its base, the outer margin (when the wing is unspread) 

 is the costa, the inner margin the dorsum, and the hinder 

 margin the termen. The angle between costa and 

 termen is the apex ; that between dorsum and termen 

 the anal angle or torniis. In the male Cockroach, 

 whose wings are well developed, the front pair are 

 in texture firm and brown, in shape narrow oblong 

 with rounded corners, while the hind pair are delicate 



