ANATOMY AND PHYSIOLOGY 91 



here females are about to emerge from the ground. Prionus also 



mbles, as Mrs. Dimmock observed in Massachusetts. In this 

 instance many males, with palpitating antennae, ran and flew to the 

 emale; moreover, a number of females were attracted to the scene. 



Sounds of Insects. Before considering the sense of hearing, 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 f and that of a common house fly is F' . From the pitch the 

 number of vibrations may be determined ; thus A ' means 440 1 vibrations 

 per second and F' , 352. The numbers thus ascertained may be verified 

 by Marey's graphic method (Fig. 76) ; 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 vibrates during respiration. 

 This " voice" should be distinguished 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 spiracular tone of the 

 same insect is at least an octave higher (A") and often rises to B" or 

 C n ', according to the state of the nervous system; in fact, it is possible 

 and even probable that various 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. 



The well-known "shrilling" of the male cicada is produced by the 

 rapid vibration of a pair of membranes, or drums, situated on the basal 

 abdominal segment, and vibrated each by means of a special muscle. 



Frictional sounds are made by beetles in a great variety of ways : by 

 the rubbing of the pronotum against the mesonotum (many Cerambyci- 

 dae) ; or of abdominal ridges against elytral rasps (Elaphrus, Cychrus) ; 

 or two dorsal abdominal rasps against specialized portions of the wing 

 folds (Passalus cornutus), not to mention other methods. In most cases 

 one part forms a rasp and the other a scraper, for the production of 

 sound. 



1 Upon the basis of C as 264 vibrations per second. The C of the physicist has 256 as 

 its frequency of vibration. 



