35 



altitude frequently corresponds, both in its fauna and 

 flora, to a higher latitude ; and that, consequently, if_we 

 ascend the niouatains_Q£,a southern land, we shall be 

 struck, at times, by the presence of a host of species 

 which obtaia at a lower level in more temperate zones. 

 This is peculiarly traceable in the Madeira Islands, — 

 which, from their subaustral position, and height (the 

 loftiest peak of the central mass exceeding 6000 feet 

 above the sea), afford a rich field to the student of zoo- 

 logical geography. Yet, though the degrees of mere 

 heat and cold are such as to allow, in the two cases, 

 species positively identical to flourish ; we should surely 

 anticipate some slight change from the different atmo- 

 spheric conditions (especially when in union with other 

 circumstances) to which they have been, through a lapse 

 of ages, respectively exposed : it may be well there- 

 fore to inquire, whether experience does at aU tend to 

 strengthen what our reason has an a priori iQclination 

 to endorse. It must be recollected however that, in the 

 instances to which we would draw attention, small aber- 

 rations are aU that can be usually looked for, since climate 

 of itself does not appear to be very potent in its action. 

 We should remember, also, that the boundaries of insect 

 instability are restricted ; and, although we would advo- 

 cate freedom of development within limits which are 

 more or less comprehensive according to the species, to 

 pass beyond them would be confusion, and such as could 

 result from a lapsus Naturae only, rather than from a 

 power of legitimate variation. 



