400 Animal Biology 



The thorax is divided into an anterior prothorax, a middle mesothorax, 

 and a posterior metathorax. The abdomen is also segmented. 



Integument and Skeleton. — A tough, flexible cuticle covers the body 

 and serves as an exoskeleton to which muscles and organs are attached 

 internally. Chitin is a protein substance (C30H50O19N4) . The cavity is 

 a hemocoel, which carries blood. 



Motion and Locomotion. — Locomotion is accomplished by two pairs 

 of wings and three pairs of jointed legs (Fig. 197). The wings consist 

 of a double layer of transparent membranes between which is a network 

 of veins to strengthen them. When at rest, the wings are folded. Dur- 

 ing flight they are extended, and the fore- and hindwings are locked 

 together by a row of tiny hooks on the front margin of the hindwings. 

 Wings may vibrate over 400 times per second during flight. 



Fig. 196. — Comb cells made by the honeybee. Note the baglike cells on the 

 surface in which the queen develops. (From PhilHps: Bees, U. S. Department 

 of Agriculture, courtesy of Bureau of Entomology and Plant Quarantine.) 



The three pairs of legs are much more specialized than those of the 

 grasshopper (Fig. 197). Because of their complexity and differences, 

 each leg will be considered separately. 



Prothoracic Leg (First): (1) An oblong coxa next to the thorax, (2) 

 a short trochanter^ (3) a long femur with branched, pollen-carrying 

 hairs, (4) a tibia with pollen-carrying hairs and a flat, movable, spinelike 

 velum, (ve' lum) (L. velum, covering), (5) a segmented tarsus, the 

 proximal segment of which may be called the metatarsus and which 



