ANATOMY AND PHYSIOLOGY IO3 



Among beetles, males of Polyphylla gather and scratch at 

 places where females are about to emerge from the ground. 

 Prionus also assembles, as Mrs. Dimmock observed in Massa- 

 chusetts. In this instance many males, with palpitating an- 

 tennae, ran and flew to the female; moreover, a number of 

 females were attracted to the scene. 



Sounds of Insects. Before considering the sense of hear- 

 ing, some account of the sounds of insects is desirable. Most 

 of these are made by the vibrations of a membrane or by the 

 friction of one part against another. 



The wings of many Diptera and Hymenoptera vibrate with 

 sufficient speed and regularity to give a definite note. The 

 wing tone of a honey bee is A' and that of a, common house 

 fly is F 1 ' . From the pitch the number of vibrations may be 

 determined; thus A' means 440* vibrations per second and 

 F', 352. The numbers thus ascertained may be verified by 

 Marey's graphic method (Fig. 74) ; he found that the fly 

 referred to actually made 330 strokes per second against the 

 smoked surface of a revolving cylinder. 



Flies, bees, dragon flies and some beetles make buzzing or 

 humming sounds by means of the spiracles, there being behind 

 each spiracle a membrane or chitinous projection which vi- 

 brates during respiration. This " voice " should be distin- 

 guished from the wing tone when both are present, as in bees 

 and flies. A fly will buzz when held by the wings, and some 

 gnats continue to buzz after losing wings, legs and head. 

 The wing tone is the more constant of the two ; in the honey 

 bee it is A', falling to E' if the insect is tired, while the spirac- 

 ular tone of the same insect is at least an octave higher (A") 

 and often rises to B" or C" ', according to the state of the ner- 

 vous system ; in fact, it is possible and even probable that vari- 

 ous spiracular tones express different emotions, as is indicated 

 by the effects produced by the voice of the old queen bee upon 

 the young queens and the males. 



1 Upon the basis of C' as 264 vibrations per second. The C of the 

 physicist has 256 as its frequency of vibration. 



