24 



universal; and whatever, therefore, be our ideas on a 

 subject which might perchance seem to be self-evident, 

 we are compelled to infer that climatal causes, of them- 

 selves, will not suffice to account for the numerous cases 

 of aberration which we so constantly meet with in re- 

 presentatives of the same species exposed, through a 

 long series of centuries, to opposite conditions of atmo- 

 sphere. We need not, however, go so far as the Gala- 

 pagos to convince ourselves of this. The Madeiran 

 Group is placed between the 32nd and 33rd parallels of 

 north latitude, off the coast of Africa, and contains a 

 Coleopterous fauna (as hitherto ascertained) of about 

 550 species. Now 240 of these, at least, occur also in 

 Europe (many of them even in our own country) ; 

 hence, if a more southern climate may be presumed, 

 of itself, to exercise any very decided modifying influ- 

 ence on insect development, we have an amount of ma- 

 terial for comparison which should surely afford us some 

 definite and tangible result. My own experience in 

 those islands would tend to prove, that, amongst the 

 many aberrations from their northern types which are 

 there everywhere displayed, comparatively few of them 

 can be referred for explanation to causes strictly climatal. 

 I do not say that none can be thus accounted for ; yet 

 I trust to make it obvious in the following pages that 

 there are even greater agencies at work than climatal 

 ones in regulating (albeit within prescribed limits, and 

 by slow gradations) the outward contour of the insect 

 tribes. 



