144 The Classification of Insects 



and the manner of life of insects to state dogmatically 

 that such characters as these can be of no value to 

 the species. For instance the difference in the feelers 

 may be no mere useless difference of shape. These 

 appendages are the seat of the senses of touch and 

 smell, and the modification of the terminal segments 

 into a club where sensory hairs are specially numerous 

 — as in T. ferrughieum — is a distinct advance on 

 the simpler feelers of T. confusum. And it is to 

 be noticed that, though both species occur together 

 in our country, the former is decidedly more common 

 than the latter, as though it were the dominant species, 

 the winner in the struggle, supplanting its less perfect 

 rival. Both these beetles have been imported into 

 North America ; there, at least in the northern 

 States, T. confusum is the more abundant of the two, 

 T. ferrughieum not having apparently been introduced 

 in sufficient numbers to press heavily on its rival in 

 that country. 



Correlation. — But if a possible use for one of the 

 specific differences between these two species can be 

 suggested, what is to be said of the other characters 

 which distinguish them — the distinction in the breadth 

 of the head and the punctures on the wing-cases ? It 

 is conceivable that characters like these, even if use- 

 less in themselves, may be correlated with useful 

 characters or qualities, may be, that is, the necessary 

 accompaniments thereof. Hence indirectly if not 

 directly they may be due to the action of natural 

 selection. 



Alternatives to Natural Selection. — But so long 

 as it is impossible decidedly to ascribe all specific 

 characters to natural selection, so long will naturalists 

 speculate on other factors of evolution. Many be- 

 lieve that the direct action of the surroundings is 

 effective not only in inducing variation but in fixing 



