CLIMATAL CONDITIONS WITH REFERENCE TO RHOPALOCERA. 99 



to their distribution, whereas in the latter the environmental 

 influence seems principally confined to species. While we thus 

 have whole genera of plants confined to particular zones upon 

 the mountains, the same in the case of animals may be com- 

 pletely cosmopolite. This conclusion will be very evident to 

 those who have made a special study of their vertical distri- 

 bution in the Alps, and is particularly so in the case of the 

 Ehopalocera. 



Thus in the latter all the principal genera are cosmopolite, 

 or nearly so. Consider, for example, Pieris, Colias, Lyccena, 

 Vanessa, Melitcea, Argynnis, Erebia, Pararge, Cmnonympha, 

 Syrichthus, and Hesperia ; while others — such, for instance, as 

 Pajnlio and Polyommatm — also possess a very wide range in 

 respect to altitude. On the other hand, the various genera of 

 plants are often considerably very circumscribed in their dis- 

 tribution, frequently being confined to only one or two zones 

 upon the mountains. The inference to be drawn from these 

 facts seems to be that the organic environment acts more 

 powerfully in the case of the animals, the physical conditions 

 manifesting their influence to a somewhat greater extent in the 

 plants. 



Now let us consider a few facts concerning the relationship 

 between altitude and morphology. 



It is too readily taken for granted similarly that butterflies 

 owe their remarkable diversity of colours and patterns to the 

 direct influence of the climatal conditions. 



Much has been written on this subject by Dr. A. R. Wallace 

 in favour of the preponderating influence of the organic en- 

 vironment. It is my intention in the present paper to confine 

 my attention to two phases only, namely, melanism and ocella- 

 tion, with special reference to the alpine Ehopalocera. 



As regards the first of these, many hypotheses have been 

 from time to time put forward to account for its existence. 

 Thus some writers of the old-fashioned school (like Mr. C. W. 

 Dale) seek to find a direct cause in the abundance of the 

 precipitation and the amount of sunshine. They assume that 

 bright colours are the direct products of the sun. How then do 

 they account for the fact of there being such a large proportion 

 of dull-coloured species of butterflies inhabiting the tropics ? 

 Take a glance, for instance, at such a work as Mr. Distant's 

 ' Ehopalocera Malay ana,' if a collection of exotic forms is not 

 available for inspection. It will be seen that the proportion of 

 dull and sombre coloured species is quite equal, indeed if it does 

 not exceed, the proportions existing in temperate climates (such 

 as that of Europe) in comparison with the number of light 

 coloured forms. Then how do they account for the following 

 fact? If we compare two species belonging to corresponding 

 groups, one of which is found in Europe or Japan, and the other 



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