114 YORKSHIRE NATURALISTS UNION. 



Unst, the most northern of the Shetland group. Mr. Jenner 

 Weir has described the results of all these expeditions,* draw- 

 ing special attention to the extreme variation in colouring 

 exhibited by these northern representatives of more southern 

 forms. 



The tendency of this variation has in almost all instances 

 been in the direction of melanism (except in the more southern 

 and western island of Arran), exhibiting a preponderance of 

 darkened scales or a suffusion of the markings, in many cases 

 almost obliterating the paler portions of the wing. Among the 

 species exhibiting this tendency in a greater or less degree may 

 be mentioned Hepiahis velleda, H. huinuli, JVoctua /estiva, JV. 

 xanthographa, Agrotis cursoria, A. porphyrea, A. hicer7iea, Dian- 

 thcecia conspersa, Evimelesia albulata, Eupithecia venosata, E. 

 nanata, Melanippe mo?itanata, M. fluduata, Cai7iptogranima 

 bilineata, &c. This same tendency is observable in the majority 

 of the Lepidoptera and, I believe, of the Coleoptera of the 

 whole Arctic and sub-Arctic regions when contrasted with their 

 more southern representatives. 



We have no sufficient evidence at present how far the 

 same rule applies to those of the Antarctic regions ; but Colias 

 imperialis Butler and Colias cunninghamii from the southern 

 extremity of Patagonia strongly favour the belief that it will be 

 found the same in those districts. 



It is worthy of remark that where the atmospheric con- 

 ditions in any degree approach to those of the more northern 

 regions, as they do on high mountain ranges, at varying eleva- 

 tions according to the degree of latitude, the same tendency to 

 assume a darker or more suffused colouring is very frequently 

 observable. 



* ' Entomologist,' xiii, pp. 249, 289 ; xiv, p. 278 ; xvii, p. I. 



Trans. Y.N.U., 1883 (pub. 1885). Series D 



