PYGOFER OF THE TETTIGTD^. 159 



tions. Whether or not such characters are selective 

 or pleasing to the artistic taste of the female must be 

 left to conjecture. 



The serrated edge of the saws in the Typhlocybidee, 

 in all the individuals I have examined, seem to lie 

 uppermost. When thrust out of the sheaths it is 

 probable, therefore, that the female, whilst forming 

 her grooves, first forces the points of the apparatus 

 forwards into the surface of the bark or leaf of the 

 plant. The muscles then, acting alternately on the 

 cutting blades, would speedily form an upward slit for 

 the purpose of oviposition. Nevertheless, I have in 

 vain attempted to see this interesting and curious 

 operation of groove-cutting. 



It is impossible to assign useful offices to many so- 

 called secondary sexual characters. The coloured 

 garniture of the beak of the turkey cock and the comb 

 of the game fowl doubtless are provocative of battle ; 

 but amongst insects we are not aware of any pre- 

 ference for what ice think beauty, neither is fierce 

 war waged amongst them for possession of the fairest. 



Dr. D. Sharp thinks that, in very early times, the 

 genital segments of insects terminated much short of 

 their present position on the abdomen. Subsequently, 

 the external male parts, with their surrounding cham- 

 bers might have come of later growth. Such a 

 growth, he thinks, might have "taken plsice pari passu 

 with the evolution of the male parts, for the purpose 

 of protection." 



Amongst the Cicadae there can be no question of the 

 existence of interlacing and interlockhig processes to 

 the pygofer. The forcible and sudden separation of 

 the sexes of Cicada septemdecem is almost always accom- 

 panied by an extensive mutilation of the parts. When 

 once the prehensile hooks have interlaced, the insects 

 seem powerless to alter the condition of things until 

 the law of increase has been approximately satisfied. 

 Thus it has happened that fossil forms in the American 

 Florissant iusect-beds remain in coitu. Catastrophes 



