418 SEXUAL SELECTION. Part II. 



of which is not understood. The sexes, also, often differ 

 in their organs of sense or locomotion, so that the males 

 may quickly discover or reach the females, and still 

 oftener in the males possessing diversified contrivances 

 for retaining the females when found. But we are not 

 here much concerned with sexual differences of these 

 kinds. 



In almost all the Orders, the males of some species, 

 even of weak and delicate kinds, are known to be highly 

 pugnacious ; and some few are furnished with special 

 weapons for fighting with their rivals. But the law of 

 battle does not prevail nearly so widely with insects as 

 with the higher animals. Hence probably it is that the 

 males have not often been rendered larger and stronger 

 than the females. On the contrary they are usually 

 smaller, in order that they may be developed within a 

 shorter time, so as to be ready in large numbers for the 

 emergence of the females. 



In two families of the Homoptera the males alone 

 possess, in an efficient state, organs which may be called 

 vocal ; and in three families of the Orthoptera the males 

 alone possess stridulating organs. In both cases these 

 organs are incessantly used during the breeding-season, 

 not only for calling the females, but for charming or 

 exciting them in rivalry with other males. No one 

 who admits the agency of natural selection, will dispute 

 that these musical instruments have been acquired 

 through sexual selection. In four other Orders the 

 members of one sex, or more commonly of both sexes, 

 are provided with organs for producing various sounds, 

 which apparently serve merely as call-notes. Even 

 when both sexes are thus provided, the individuals 

 which were able to make the loudest or most continuous 

 noise would gain partners before those which were less 

 noisy, so that their organs have probably been gained 



