16 INTRODUCTION. 



Onthopliagns rangifer bears u[)on the head a pair oE long chitinous 

 filaments streaming backwards almost horizontally and knobbed at 

 the ends, while in the South American Golofa porteri the head 

 and thorax each bear a very slender and brittle rod standing 

 up vertically. It has been pointed out that such extravagant 

 outgrowths are often found in fossil animals of races which have 

 no present day representatives, a possible reason for their total 

 disappearance being that the hypertrophy has reached a stage of 

 such serious inconvenience as to result in the ultimate extinction 

 of the race in competition with others not so handicapped. Perhaps 

 they are best regarded as analogous to some characteristics 

 of the aristocracy in certain races of mankind, such as the con- 

 tracted feet and long nails of the Chinese, that is, as practical 

 inconveniences endured with satisfaction as the proofs of an idle 

 existence. In the female beetles, which have always the duty of 

 j)roviding for the succeeding generation, frequently involving very 

 laborious and complicated operations, and in such males as co- 

 operate, as many do, in these labours, the operation of Natural 

 Selection ensures the development of every part of the body upon 

 strictly utilitarian lines and the perpetuation of any impeding out- 

 growths is impossible ; but when tliese functions ars confined to 

 one sex this factor operates upon that alone, and the forces which 

 produce variation, whatever they may be, taking the path of least 

 resistance, seem to concentrate upon the features thus left free 

 to them. 



A frequent sexual difference in the form of the front tibiae will 

 illustrate this idea. In the females these are nearly always broad 

 and strong and provided with sharp teeth at the outer edge, an 

 effective digging implement resulting. In Passalid^, where 

 there is an equal division of labour between the sexes, and in 

 many other Laraellicornia, no difference is found in this respect, 

 but in a very large number these limbs are more slender in the 

 males, and the teeth are either absent or so spaced as to be evidently 

 less serviceable. Every stage of disparity can be found in different 

 species from one scarcely perceptible until a grotesque degree of 

 elongation is reached in the male. The process has attained its 

 limit in the strange genus Euchlrus, of which there are two 

 Indian species. 



An interesting phenomenon in connection w ith these character- 

 istics of the male sex is the relation between the degree of their 

 development and the size of the insect, both individualh' and 

 specifically. The maximum development is only found in the 

 largest specimens of their kind and a regular diminution accom- 

 panies diminished size of the individuals, until in very dwarfed 

 specimens these features may be absent altogether. A similar, 

 but less exact, correspondence can be traced in the relative sizes 

 of the species of a group. The smaller forms are almost always 

 without well-marked secondary sexual features, which become 

 most accentuated in the giant forms. This is well illustrated in 

 the Cetoxiix.'e and Dyxastix.?:. 



