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so complex that definition seems almost impossible. Not 

 only must the condition of soil, climate (in all its local 

 modifications), position, and surrounding fauna and flora be 

 considered, but the relation of the individual constituents of 

 the latter to the species under consideration must also be 

 taken into account. Hence it happens that two different 

 organisms occupying the same ground may, owing to a 

 difference in habit, have two entirely different environments, 

 with a difference of food-plant, different enemies, &c., and it 

 is clear that the competition with other forms of animal life 

 must react on almost every species in an entirely different 

 way ; whilst in the same little corner of a field or wood the 

 larva, the pupa, and the imago of any common butterfly are 

 subjected to three entirely different environmental conditions. 

 Nothing is more discontinuous possibly than the environ- 

 ments of certain species when the habitat of such a species 

 is compared with the neighbouring districts, both with 

 regard to its inorganic condition and the organic beings 

 peopling it. Hundreds of acres of waste ground occur in 

 Britain, yet Anthrocera vicice occurs only in a limited portion 

 of the New Forest, an apparently continuous environment 

 not leading to the spread of the species. Nothing can 

 illustrate better the discontinuity of environment. A. vicice 

 occurs in the New Forest, again at Rheims, again at Cauterets 

 in the Pyrenees, and nowhere probably between (or if there 

 are other localities they are perfectly separate from each 

 other). It occurs again in North Germany, in Pomerania, 

 and in the Baltic provinces. From the New Forest we have 

 to skip some hundreds of miles before we come to suitable 

 spots where A. vicice finds an environment suited to its 

 peculiar requirements. Whether it be specialised to some 

 particular food-plant, all other favourable circumstances 

 being useless in the absence of this, we do not know, but it 

 is evident that its environments are discontinuous in every 

 possible meaning of the term. That the conditions of 

 environment— climatic, inorganic, organic — acting on an 

 already plastic and variable organisation is the primary 

 cause of specialisation, leading up to the development of 

 species, we feel certain that no competent and logical field 

 naturalist would venture to dispute. 



It often seems to be overlooked that the variations in 

 species are indefinite in number, that the internal functions 

 of the organism itself possibly give rise to the variations, 

 that such variations as are useful to the species are moulded 

 into the directions required, by natural selection, that every 



