CflAP. XI. Summary on Insects. 327 



to the several Orders, we see that the sexes often differ in 

 various characters, the meaning of which is not in the least 

 understood. The sexes, also, often differ in their organs of 

 sense and means of locomotion, so that the males may quickly 

 discover and reach the females. They differ still oftener in 

 the males possessing diversified contrivances for retaining the 

 females when found. We are, however, here concerned only in 

 a secondary degree 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 it 

 probably arises, that it is in only a few cases that the males have 

 been rendered larger and stronger than the females. On the 

 contrary, they are usually smaller, so that they may be developed 

 within a shorter time, to be ready in large numbers for the 

 emergence of the females. 



In two families of the Homoptera and in three of the Orthop- 

 tera, the males alone possess sound-producing organs in an 

 efficient state. These are used incessantly during the breeding- 

 season, not only for calling the females, but apparently for 

 charming or exciting them in rivalry with other males. No 

 one who admits the agency of selection of any kind, will, after 

 reading the above discussion, dispute that these musical instru- 

 ments 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. 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 producing sound, possessed by the males alone, or by both 

 sexes, in no less than six Orders. We thus learn how effectual 

 sexual selection has been in leading to modifications which 

 sometimes, as with the Homoptera, relate^ to important parts of 

 the organisation. 



From the reasons assigned in the last chapter, it is probable 

 that the great horns possessed by the males of many Lamel- 

 licorn, and some other beetles, have been acquired as ornaments. 

 From the small size of insects, we are apt to undervalue their 

 appearance. If we could imagine a male Chalcosoma (fig. 16), 

 with its polished bronzed coat of mail, and its vast complex 



