INSECTS 127 



pollen from the pollen baskets located on the metathoracic legs. A 

 pollen brush is also present. The tarsus of the mesothoracic leg, 

 however, lacks both the antenna comb and the eye brush. 



Metathoracic Legs. This pair of legs possesses a number of 

 interesting adaptations. The tibia is modified to form a large 

 cavity, the pollen basket, which runs the entire length of the 

 segment. It consists of a depressed area on the outer surface, in 

 which the pollen is placed. The pollen is held there by hairs 

 which arise on the edges of the tibia and which curve over the 

 edges of the underlying depression in such a way as to keep the 

 pollen grains firmly in position. The distal end of the tibia, 

 where it joins with the tarsus, has a series of spines which consti- 

 tute the pecten. These fit into a special structure, the auricle, 

 on the proximal edge of the tarsus. On the inner side of the basi- 

 tarsus are the pollen combs, which consist of several rows of 

 regularly arranged bristles. The latter are used to hold some of 

 the pollen before it is transferred to the pollen basket. 



3. Abdomen 



Although the abdomen of a typical Insect consists of ten or 

 eleven segments, the external divisions of the exoskeleton in the 

 Bee show only six. Each segment consists of an enclosing band 

 of the chitinous exoskeleton which, when seen in a transverse 

 section, shows the same general plan of structure as is found in the 

 abdominal segments of the Grasshopper, with a dorsal plate, or 

 tergum, and a ventral plate, or sternum. The separate exoskel- 

 etal rings are connected and articulated with each other by the 

 flexible end tissues so that a considerable movement may be 

 brought about by the action of the abdominal muscles. The 

 sterna on the four posterior segments possess a pair of ventral 

 openings which are connected with the internal wax glands, and 

 through which the wax is secreted. 



At the extreme posterior end of the abdomen, enclosed within 

 the body wall, is a very complex organ for defense, the sting. 

 There is an elongated, chitinous rod, the sheath, and a pair of 

 darts with saw-toothed edges, one of which lies on either side of the 

 sheath. Laterally, there is a pair of fleshy, hair-covered structures 

 provided with sense organs, the feelers. The feelers locate a fa- 

 vorable region on the animal that is being attacked, and then the 

 sheath with the darts is forced down into the tissues at the spot 



