80 



that it is not from its failure, in either instance, that 

 contending results are brought about, but simply that 

 some counteracting agent has been exerting its energy 

 in the one case, so as to nullify what would have other- 

 wise come to pass. 



The main object however of the present section being 

 to show that a considerable amount of power is due to 

 isolation itself, in regulating (after a long series of ages) 

 the outward aspect of the insect tribes, it is not strictly 

 necessary that we should so rigidly insist on deteriora- 

 tion of size as one of its primary consequences, since 

 (whether it be so or not) we are merely concerned here 

 to demonstrate, that its influence, in some shape or other, 

 is absolute and real. 



After the above remarks, we shall not be surprised 

 that the phenomena displayed in certain islands, as 

 regards size, are sometimes (though I believe it to be an 

 exception to the ordinary rule) the exact opposite of 

 what we have been describing. Let us not however be 

 alarmed at this fact, on the bare statement of it, as 

 though the proposition which we have been lately ad- 

 vancing were at once disproved ; since we shall find, on 

 inquiry, that the case is not so desperate as might be 

 imagined; and that in many islands where even this 

 principle is to be detected, we may recognize traces of 

 the other also. But how, it will be asked, can this be ? 

 for, since the influences are the same, creatures simi- 

 larly exposed to them must be similarly affected. Now, 

 although, on a broad scale, suck a notion contains much 



