Chap. XL] SUMMxVRY OX INSECTS. 405 



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 fe- 

 males. 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 pos- 

 sess, in an efficient state, organs which may be called vo- 

 cal; 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 agen- 

 cy 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 through sexual selection. It is instructive to 

 reflect on the wonderful diversity of the means for produ- 

 cing sound, possessed by the males alone or by both sexes 

 in no less than six Orders, and which were possessed by at 

 least one insect at an extremely remote geological epoch. 

 We thus learn how effectual sexual selection has been in 

 leading to modifications of structure, which sometimes, as 

 with the Homoptera, are of an important nature. 



For the reasons assigned in the last chapter, it is prob- 

 able that the great horns of the males of many lamellicorn, 

 and some other beetles, have been acquired as ornaments. 

 So perhaps it may be with certain other peculiarities con- 



