BEETLES THAT "BLUFF" 223 



prolonged for fifteen or twenty seconds, gradually in- 

 creasing and decreasing in force. 



Curiously enough, no special auditory organs have yet 

 been discovered, and it has been suggested that these 

 insects do not hear in our sense of the word, but feel 

 rhythmical vibrations. But whether the males "sing in 

 rivalry," as Dr. David Sharp suggests, is another matter. 

 The purpose of the " song " in the first place is no doubt 

 intended as a guide to the females seeking mates. But 

 it is quite conceivable that the call of one male may 

 stimulate every other male in the neighbourhood. Darwin, 

 commenting on this aspect of the music, gives a quotation 

 from Dr. Hertman, who says : " The drums are now . . . 

 heard in all directions. This I believe to be the marital 

 summons from the males. Standing in thick chestnut 

 sprouts about as high as my head, where hundreds were 

 around me, I observed the females coming around the 

 drumming males. . . . This season a dwarf pear-tree 

 in my garden produced about fifty larvae of Cicada 

 pruinosa ; and I several times noticed the females alight 

 near a male while he was uttering his clanging notes." 



The structures, he remarks, from which these sounds 

 proceed, " must be ranked amongst the most remark- 

 able voice-organs in the animal kingdom. They are 

 totally different from the stridulating organs that are 

 found in many other insects. . . . Some difference of 

 opinion has existed as to the manner in which the 

 structures act, but the account given by Carlet . . . will, 

 we believe, be found to be essentially correct." They 

 are partly thoracic and partly abdominal. On examining 

 a male Cicada there will be seen, on the under surface, 

 two plates, meeting in the middle line of the body and 

 overlapping the base of the abdomen. They can be 



