INSECT STRUCTURES 17 



mouth as with the vertebrates, and frequently accom- 

 panied by specialized hairs which may be found on the 

 palpi, outside the mouth cavity. The hypopharynx is the 

 main organ for the sense of taste. 



The sense of smell is known to be located in the an- 

 tennae of many species. In others its organs are not cer- 

 tainly identified. Hearing organs occur in highly unex- 

 pected places. Male mosquitoes hear with the antennas. 

 An ear drum or tympanum is located on the first segment 

 of the abdomen in grasshoppers, while it is found on the 

 tibia of some crickets. In some insects the location of 

 the sense of hearing is not known, but it seems certain 

 that all forms are able to perceive sound. Of all the 

 special senses smell is usually most highly developed. 



Many forms of body covering are noted. These are 

 largely protective. The body hairs of some insects are con- 

 nected with poison glands or are barbed or covered with 

 some irritating substance. The larvae of the Brown-tail 

 moth have barbed hairs which cause an itch or rash on 

 the human skin and so render them a great nuisance. 



Scent glands are often present. These may be pro- 

 tective or they may serve to attract the mates. The 

 latter is the case in certain moths while in many bugs 

 and some beetles and butterflies the scents secreted pro- 

 tect from natural enemies by making the insects dis- 

 tasteful. 



A special structure of much interest is the silk-pro- 

 ducing apparatus. This consists of a pair of silk glands 

 opening through little holes just beneath the mouth. 

 These glands resemble the salivary glands but are larger. 

 Other glands secrete such substances as the honey-dew 

 of Aphids and related insects, the wax covering of the 

 scale insects and Lac, also a product of scale insects. 



