THE LEPIDOrTERA OF PERTHSHIRE. 81 



seems to show that it stretched to the Feroe Isles, and it 

 would be much to be desired that some self-sacrificing Ento- 

 mologist should spend a summer in these islands, and see 

 what species and varieties are there taken; the facts learnt 

 by such a sojourn might prove of more value than a collection 

 of specimens. We want much such a list as the present 

 from Sutherland and Caithness. 



Some interesting remarks are made on the subject of 

 boreal variations. Dr. B. White shows that, in Perthshire, 

 the rainfall has much to do with their production. It is 

 curious to note under what conditions changes of colour 

 occur in species ; but in noting this we must bear three 

 things in mind : firstly, that climatic changes do not imply 

 of necessity that either climate should be Alpine or boreal — 

 thus a species often differs much when taken in the south of 

 England from the same insect taken in the south of Europe ; 

 secondly, isolation from any cause always increases the ten- 

 dency, and a different race is much more likely to occur 

 when species breed in and in, than when fresh blood from 

 extraneous sources is constantly being introduced ; and, 

 thirdly, variation is not uniform — though an Alpine variation 

 is generally darker, such is not necessarily the case. Pre- 

 mising these things, we may sum up the known causes of 

 colour- variation under the following heads : — 1. Climate ; 

 2. Altitude ; 3. Amount of cloud, or rainfall ; 4. Season of 

 the year ; o. Smoky towns. It is easy to see what induc- 

 tion must be drawn by any one who has read his Bacon as 

 to the real cause in the matter. 



Variations in size are different, and the following recipe 

 will always produce such, according to my experience : breed 

 from the ^^^^ and supply the larva with a short allowance 

 of food in its early days, then feed it up well, or it will die 

 in the pupa stage ; the perfect insect will be invariably 



1873. G 



