ON THE PROFUSION OF RHOPALOCERA IN THE ALPS. 287 



flourish vines, maize, and tobacco ; then walnuts and sweet 

 chestnuts, beeches, oaks, and wheat ; above them, forming a very 

 broad belt, the great tract of conifers ; then brilliant-coloured 

 alpine flowers and lichens, until we arrive at the perennial snows 

 of the higher mountain peaks. These represent isothermal 

 differences as great as exist between Italy in the one direction 

 and the polar regions in the other. 



To the entomologist who has only been accustomed to 

 collecting on this side of the English Channel, whose experience 

 has been confined to no better fare than what the New Forest 

 can afford, tlie Alps constitute a perfect El Dorado of butterfly 

 abundance and beauty. It is true that the general facies of the 

 rhopalocerous fauna does not differ so much from that existing in 

 these humid isles, but the great interest accrues in the number 

 of closely allied forms occurring there, side by side with the more 

 familiar ones of our own woods, fields, and commons, thereby 

 affording abundant material for the student of evolution and 

 morphology, as well as a more extensive series of species for the 

 collection. What does the British entomologist know, for 

 instance, of such typical genera as Erebia, Syrichthus, Satyrus, 

 Melitcea, Chrysophanus, with their miserable quota of 2, 1, 1, 3, 

 and 1 species respectively, compared with their corresponding 

 numbers in the Alps, namely 25, 7, 8, 11, and 10, in addition to 

 as many more local races and well-marked permanent geographical 

 varieties ? 



Compared with many parts of the tropics, however, the 

 Alps of course constitute a poor collecting-ground as regards 

 the number of species occurring upon them. But like most 

 other portions of the Palsearctic area, what they lack in variety 

 of forms and specialisation is fully made up in the great quantity 

 of individuals of many species which exist upon their slopes. 



It will be found a general rule, that the further we recede 

 from the tropics the less number of species we are able to meet 

 with ; on the other hand the number of individuals increases, the 

 differences reaching their extremes at the equator in the one direc- 

 tion and in arctic regions in the opposite. The Alps constitute 

 no exception to this law, in fact they furnish a very good 

 illustration of the subject under consideration. In the lower 

 valleys which constitute the equivalent of the temperate zones 

 by far the most species are to be found, but it is at the alpine 

 elevations which represent the arctic regions of the horizontal 

 isotherms where individuals generally abound to the greatest 

 degree. It is perfectly astonishing with what profusion some 

 species are to be met with in good localities upon the mountains, 

 such, for instance, as Pieris caUldice, Colias jjhicomone, Chryso- 

 phanus virgaurece, Melitcea didyma, M. dictynna, M. parthenia, 

 Argynnis pales, A. niobe, A. amathusia, Coenonympha satyrion, 

 Satyrus cordula, in addition to a great many species of Erebia 



2b 2 



