284 



THE DESCENT OP MAN. 



Fig. 14. Hind-leg- of Stenobotli- 

 rus pratorum: r, tiie stridu- 

 lating ridge; lower figure, the 

 teetli forming the ridge, much 

 magnified (from I^andois). 



elastic teeth, from 85 to 93 in number;" and these are scraped 

 across the sharp, projecting nervures on the wing-covers, which 



are thus made to vibrate and re- 

 sound. Harris" says that when 

 one of the males begins to play, 

 he first "bends the shank of 

 "the hind-leg beneath the thigh, 

 "where it is lodged in a furrow 

 "designed to receive it, and then 

 "draws the leg briskly up and 

 "down. He does not play both 

 "fiddles together, but alternately, 

 "first upon one and then on the 

 "other." In many species, the 

 base of the abdomen is hollowed 

 out into a great cavity which is 

 believed to act as a resounding 

 board. In Pneumora (flg. 15), a 

 S. African genus belonging to the 

 same family, we meet with a 

 new and remarkable modification; 

 in the males a small notched 

 ridge projects obliquely from each side of the abdomen, against 

 which the hind femora are rubbed.'" As the male is furnished 

 with wings (the female being wingless), it is remarkable that the 

 thighs are not rubbed in the usual manner against the wing- 

 covers; but this may perhaps be accounted for by the unusually 

 small size of the hind-legs. I have not been able to examine the 

 inner surface of the thighs, which, judging from analogy, would 

 be finely serrated. The species of Pneumora have been more pro- 

 foundly modified for the sake of stridulation than any other 

 orthopterous insect; for in the male the whole body has been 

 converted into a musical instrument, being distended with air, 

 like a great pellucid bladder, so as to increase the resonance. 

 Mr. Trimen informs me that at the Cape of Good Hope these 

 insects make a wonderful noise during the night. 



In the three foregoing families, the females are almost always 

 destitute of an elficient musical apparatus. But there are a few 

 exceptions to this rule, for Dr. Gruber has shown that both sexes 

 of Bphippiger vitium are thus provided; though the organs differ 

 in the male and female to a certain extent. Hence we cannot 

 suppose that they have been transferred from the male to the 

 female, as appears to have been the case with the secondary sexual 



«Landois, ibid. s. 113. 



"■ 'Insects of New England,' 1842, p. 133. 



" Westwood, 'Modem Classification,' vol. 



p. 462. 



