SPECIAL SENSES 13 



to their different modes of life. In the sucking forms, such as 

 mosquitoes and squash bugs, the insects suck the blood of animals 

 or the juice of plants, piercing the surface with the mouth parts. 



The thorax or middle part of a typical insect's body really con- 

 sists of three sub-parts: the prothorax, bearing the front pair of legs; 

 the mesothorax, bearing the front pair of wings and second pair of 

 legs, and the metathorax, from which spring the hind pair of legs 

 and posterior pair of wings (Fig. 8) . 



The leg of a typical insect consists of the following joints: a 

 small globular joint next to the body called coxa, then a long joint, 

 generally the larger, called the femur* then a slender, long joint 

 known as the tibia, and finally the tarsus, consisting typically of 

 five joints, the last bearing two tiny claws. Between these claws 

 is a pad-like appendage called the pulvillus (Fig. 10). 



FIG. 9. Surface view of the facets of a FIG. 10. Two types of the last tarsal 



compound eye, much enlarged. joint. The pulvillusin figure on right is pad- 



like; in the figure on left it is represented 

 by a bristle. 



The abdomen. Behind the thorax is the abdomen of a vary- 

 ing number of segments. On the sides of the abdomen and the 

 sides of the thorax occur the spiracles, openings leading into the 

 trachea! system through which the adult insect obtains its supply 

 of oxygen. It is to be noted, however, that insects will live a long 

 time without oxygen. The posterior end of the abdomen may 

 exhibit appendages, notably the ovipositor in the female grass- 

 hopper or the sting (modified ovipositor) in wasps or worker bees. 



The hard, outer part of an insect's body (called exoskeleton) 

 is composed of a horny substance, called chitin. 



Special Senses. The sense of sight in insects is probably very 

 primitive, as are also the other special senses. The sense of hearing 

 exists in pits in the antennae, or in special organs on the first seg- 

 ment of the abdomen, or in the tibice of some Orthoptera. That 

 insects can hear is evidenced by the fact that we find sound-produc- 

 ing mechanisms, which would not exist unless there also existed the 

 means of hearing the same. The sense of smell is located in olfac- 



*A very small segment, sometimes well marked, between coxa and femur, 

 is called the trochanter. 



