uj(lIBRAR Y 



ZOOLOGY. 



THE MOUNTAIN LEPIDOPTEKA OE BRITAIN : THEIR 

 DISTRIBUTION AND ITS CAUSES. 



By F. BUCHANAN WHITE M.D., F.L.S. 



THE distribution of species, either of plants or of animals, 

 is of a twofold character, — firstly, as regards space, and 

 secondly, as regards time, the former of these being again capable 

 of subdivision into latitudinal and longitudinal distribution, and 

 altitudinal distribution ; but between the latitudinal and altitu- 

 dinal distributions a close relationship exists. 



In ascending a high mountain and observing the various 

 degrees of temperature and climate, with the accompanying 

 vegetation, that are successively experienced as we pass from 

 the base to the summit — the olive-trees and vines, myrtles and 

 oleanders, that occupy the lowest parts ; the chestnuts and oaks 

 that perhaps come next, followed in succession by fir-trees, open 

 pastures, moss and lichen covered soil ; and, finally, at the sum- 

 mit, by eternal snow — it does not require any great stretch of the 

 imagination to fancy that the terrestrial globe resembles in many 

 aspects two great mountains cohering by their bases at the 

 equator, and culminating at the poles in summits covered with 

 eternal ice and snow. As we proceed from the equator to either 

 pole, we pass through zones of climate and vegetation similar to 

 what we did in ascending the mountain, and find that each has 

 sufficiently well-marked limits characterised by special forms of 

 animals and plants. 



But many mountains have more than one summit or peak, not 

 so high or so extensive as the real or central peak, and on each 

 of these secondary summits we find repeated, though possibly on 

 a smaller scale and in a less degree, the features of vegetation 

 presented by the whole mass. And so it is with the two imagi- 

 nary hills that form the terrestrial globe. They have many 

 smaller peaks (in other words, mountains), each of which pre- 



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