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ON SOME 



PROBABLE CAUSES OF A TENDENCY 



TO MELANIC VARIATION IN LEPIDOPTERA 



OF HIGH LATITUDES. 



By the Rt. Hon. LORD WALSINGHAM, M.A. ; 



BEING THE ANNUAL ADDRESS OF THE PRESIDENT TO THE MEMBERS OF THE 

 YORKSHIRE NATURALISTS' UNION, AT DONCASTER, MARCH 3RD, 1885. 



Those of you who have taken any interest in the study of Lepi- 

 doptera are well aware that in the course of the last four years 

 some very interesting collections have been made in the most 

 northern parts of the British Islands. Since the rapid increase 

 in the number of our collectors has rendered the capture of a 

 species new to our lists a very rare occurrence, greater attention 

 has been devoted to the geographical distribution and local 

 variation of well-known forms. The Scotch mountains pro- 

 duced a not unprofitable harvest for such enterprising profes- 

 sional collectors as were early in the field, and so soon as 

 Scotch varieties of most of our English Lepidoptera were repre- 

 sented in our best collections, the inducement was strong (and 

 this by no means only a commercial one), to explore further 

 afield and to provide the means of comparing specimens 

 obtained from the northern and western islands of Scotland 

 with those procured at various elevations on the mainland. 



In 1880 a collector, sent by Mr. Meek, brought back, after 

 four months' residence in the Shetland Isles, a considerable 

 collection. These were noticed at length by Mr. J. Jenner Weir 

 in the November and December numbers of the ' Entomologist ' 

 of that year. The interest excited by this collection induced the 

 same collector, Mr. McArthur, to revisit the islands in 1881, 

 to make an expedition to the Island of Arran in the following 

 season, and to spend three months of 1883 in the island of 



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