326 THE DESCENT OF MAN. 



less) it is remarkable that the thighs are not rubbed in the 

 usual manner against the wing-covers; but this may per- 

 haps be accounted for by the unusually small size of the 

 hind legs. I have not been able to examine the inner sur- 

 face of the thighs, which, judging from analogy, would be 

 finely serrated. The species of Pneumora have been more 

 profoundly 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 dis- 

 tended 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 efficient musical apparatus. But there 

 are a few exceptions to this rule, for Dr. Gruber has shown 

 that both sexes of EpMppiger vitium are thus provided; 

 though the organs differ in the male and female to a cer- 

 tain 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 characters of many 

 other animals. They must have been independently devel- 

 oped in the two sexes, which no doubt mutually call to 

 each other during the season of love. In most other Locus- 

 tidae (but not according to Landois in Decticus) the females 

 have rudiments of the stridulatory organs proper to the 

 male; from whom it is probable that these have been trans- 

 ferred. Landois also found such rudiments on the under 

 surface of the wing-covers of the female Achetidse, and on 

 the femora of the female Acridiidae. In the Homoptera, 

 also, the females have the proper musical apparatus in a 

 functionless state; and we shall hereafter meet, in other 

 divisions of the animal kingdom, with many instances of 

 structures proper to the male being present in a rudimentary 

 condition in the female. 



Landois has observed another important fact, namely, 

 that in the females of the Acridiidae, the stridulating teeth 

 on the femora remain throughout life in the same condition 

 in which they first appear during the larval state in both 

 sexes. In the males, on the hand, they become further 

 developed, and acquire their perfect structure at the last 

 moult, when the insect is mature and ready to breed. 



From the facts now given we see that the means by 



