PROGRESSIVE MELANISM IN LEPIDOPTEEA. 251 



frequent at Huddersfield, but, although it occurred at Sheffield in 

 1896, it seems not to have increased at all, and in some woods near 

 the town it has never been recorded. Other cases of the same kind 

 are given for P. chi, etc. It is possible that where melanic varieties 

 are found in widely separated areas, they have arisen independently 

 in each locality, and this is certainly true in some cases, e.g., Venmia 

 cambrica, for, in this species, the dark variety found in the Sheffield 

 district is very different from that taken at Middlesborough. 

 Similarly, Barrett has described several distinct varieties of 0. 

 bidentata, which seem to be characteristic of different localities. 



In cases in which melanism has increased in comparatively 

 recent years, the rate of increase in the melanic area, and the rate of 

 spreading of the melanism into districts previously unaffected, vary in 

 different species. From the evidence received, some idea may be 

 gained as to the rate of increase in some species, e.g., A. hetularia, 

 P. pilosaria, H. progenmraria, and, in London, of E. rectangidata, but 

 in general it is not yet easy to get definite facts which shall determine 

 exactly how fast the change proceeds. What is needed more than 

 anything else is that, on the outskirts of the melanic area for any 

 species, i.e., especially in the Midlands and around London, observers 

 should each year collect a considerable sample at random, so that the 

 percentage of melanics for every year should be known with accuracy. 

 With common species, such as H. progenimaria, P. chi, X. polyodon 

 and others, this could be done without difficulty, and would lead to 

 most valuable results in the course of a few seasons. It wouJd also 

 help to solve the problem as to whether melanics are more frequent in 

 some seasons than in others, about which, at present, very little is 

 certainly known. 



It is well-known that the areas in which melanism is most frequent 

 are either in the neighbourhood of large towns and manufacturing 

 districts, or are characterised by heavy rainfall and damp climate. It 

 seems, from the records received, that the most conspicuous cases of 

 pnogressive melanism, in which there has been a notable increase since 

 it was first observed, are those which have arisen under urban condi- 

 tions. Examples of this are A. betularin, P. pilosaria, H. abruptaria, 

 E. rectangidata, A. psi, and P. chi. In A', polyodonand C. hilineata the 

 chief melanic areas are in places with heavy rainfall, viz., west of Ireland 

 and Scotland, but in X. polyodon there is evidence that melanism is in- 

 creasing in the manufacturing districts of the north of England. Some- 

 what similar cases are 0. bidentata and M. strigilis, both of which have 

 dark varieties in districts far removed from smoke, but show an increase 

 of melanism in smoky localities. A remarkable example of melanism, 

 arising quite apart from smoke, is that observed by Mr. Goodwin in 

 T. consonaria a,nd T. consortaria, in Kent. A. nebulosa is perhaps also 

 exceptional ; as in many other species, it is darker in the north of 

 England than in the south, and this was probably the case before 

 manufacturing towns existed, but its most extreme black form 

 occurs at Delamere, where there is not much smoke, and in Scotland 

 the fully light type found in the south reappears. Delamere is a 

 melanic centre for other species also, e.g., M. liturata, but it does not 

 seem to be characterised by either excessive smokiness or rainfall. 



Although there are, perhaps, not many cases of melanism which 

 have arisen in districts where there is neither smoke nor excessive 



