102 THE ENTOMOLOGIST. 



the results of close breeding, as induced sometimes in nature by 

 isolation, as in the case of an island or alpine valley ; or 

 artificially, as in the instance already cited of the aberrant 

 melanic forms of T. crepuscularla and biimdularia, which have 

 become permanent varieties, if not species, I am given to under- 

 stand, in a wood in the neighbourhood of Barnsley, where they 

 replace the normal type. 



" Of the remote and primary causes of variation we as yet know 

 but little with certainty, except in the case of the presence or 

 absence of sunlight and heat, which without doubt is most potent 

 in the development or degeneration of colour and distinctness of 

 pattern ; acting, as we have seen, inversely in the case of the 

 nocturnal and diurnal divisions of Lepidoptera. 



"As to the effect of diversity of food, I have ventured to 

 express my belief that, with certain] exceptions, it is not 

 directly apparent in individuals, though, in common with other 

 causes, it may eventually leave its impress on a race. But that 

 its abundance or scarcity acts powerfully on the size and vigour 

 of the insect in every stage is undeniable. 



" As to those strange topographical characters, two cases of 

 which I have brought under your notice, which are possessed in 

 common by a number of insects peculiar to a particular district, 

 I do not venture a suggestion, unless that in some way the law 

 of mimicry, that most inexplicable of all natural powers, has 

 asserted itself." 



The paper was then brought to a close by an appeal for more 

 systematic scientific work ; that facts bearing upon the topics 

 reviewed that evening might be collected and written down as 

 they occur, and that in forming collections more attention should 

 be paid to local aberrations, and phenomena relating to the life 

 history of any insect, no matter how common and well known. 

 The possession of long series of variable insects was strongly 

 recommended, the locality and date of capture of each specimen 

 being indicated by a number referring to the entomologist's 

 memorandum book ; and the author referred to Mr. Bond's 

 magnificent collection as being one of the few English ones 

 which had been formed on such principles, and possessed a 

 scientific interest of great value to a student of the laws of 

 Nature. 



