82 



Insects and Disease 



of the whorl of dense, fine, long hairs on each 

 segment. Another interesting difference in the 

 antennae is to be noted in the size of the first joint. 

 In both sexes it is short and cup-shaped, but in the 

 male it is somewhat larger. This basal segment 

 contains a highly complex auditory organ which 

 responds to the vibrations of the whorls of hairs 

 on the other segments. Interesting experiments 

 have shown that these hairs vibrate best to the 

 pitch corresponding to middle C on the piano, the 

 same pitch in which the female " sings." Of 

 course mosquitoes and other insects have no voice 

 as we ordinarily understand the word, but produce 

 sound by the rapid vibration of the wings or by the 

 passage of air through the openings of the tracheae. 

 The males and females are thus easily distin- 

 guished and, as we shall see later, this is of some 

 importance for only the females can bite. The 

 males and females differ in another way. Just be- 

 low the antennae and at the sides of the proboscis or 

 beak is a pair of three- to five-jointed appendages, 

 the maxillary palpi or mouth-feelers which in the 

 females of most species are very short (Fig. 64) 

 while in the males they are usually as long as 

 the proboscis (Fig. 65). The females of Anopheles 

 and related forms have palpi quite as long as the 

 males, but they are slender throughout while the 



