166 THE entomologist's RECORD. 



might appear, and, by increasing in abundance, succeed in replacing 

 the type to a greater or less extent. On this point the evidence differs 

 considerably in the respective species, and no answer generally 

 applicable to all can be made. 



In considering the problem of the causation of such evolutionary 

 change, it is necessary to distinguish carefully between the cause, in the 

 strict sense, which leads to the appearance of the variations, and the 

 circumstances, which, by favouring these variations, have enabled them 

 to persist, and may thus, in a secondary sense, be spoken of as causes 

 of the change of type. Though from the simultaneity of the appear- 

 ance of similar varieties in so many distinct species, it is difficult to 

 resist the conclusion that some of these effects are due to a definite 

 cause, it was not anticipated that, in the absence of any clue, the 

 present inquiry would succeed in elucidating this part of the problem. 



There was, however, some hope that the evidence would throw 

 light on the circumstances which have contributed to the persistence of 

 the melanics. The fact that, in so many cases, the progress of the 

 change has taken place chiefly in or near manufacturing centres, 

 naturally suggests a relation of cause and efiect, and the circumstance 

 that, after their appearance on the continent, these forms have especially 

 established themselves in the neighbourhood of Crefeld, the "black 

 country " of Germany, supports the same conclusion. As appears from 

 the details, it nevertheless is not possible to press this deduction very 

 closely, for, in several instances, melanics have become prevalent in 

 quite rural localities. Moreover, even granting the connection between 

 urban conditions and melanism, the further inference that the success 

 of the melanics is to be ascribed to their protective coloration remains 

 very doubtful. Though having a certain plausibility, this suggestion 

 is extremely difficult to apply in detail, and, for the present, we are 

 scarcely entitled to go beyond the general conclusion, that, in some 

 unknown way, the change from rural to urban conditions has contributed 

 to the predominance of melanic forms. 



Summaries are given below of the records received with regard to 

 the respective species. 



Odontopera BmENTATA. — Melanic forms are taken in Scotland, the 

 northern counties of England, Yorkshire, Lancashire, and Ireland, 

 isolated specimens further south. Quite black specimens occur in the 

 West Eiding (Huddersfield, etc.). According to Barrett, in different 

 localities the darkening takes different forms, e.g., smooth, smoky-black 

 in Lancashire, darkening especially outside the second transverse line 

 in Ireland. Forres, moderately dark (Hewett). Wigtownshire, quite 

 light, few ; intermediates more frequent, dark, with strong markings, 

 few (Gordon). Newcastle, typical brown form prevalent, about 20% 

 suffused, some with markings barely visible ; larvfe generally nearly 

 black (Nicholson). Sunderland, typical brown form, rather dark, but 

 little variation (Brady). Hartlepool, generally light, a few dark, and a 

 local banded race exists (Eobson). Huddersfield, 45 years ago, light 

 prevalent, now rather dark brown is commonest, not infrequently suffused 

 Avith black, occasionally nearly black (Mozley). Wakefield, unicolorous 

 black occurs ; Hull, dark occurs (Hewett). Manchester, pale to black, 

 medium prevalent (Kearcy). Cheshire, light prevalent, medium 

 common, dark less common (Arkle). Worksop (Alderson), Sledmere 

 (Hewett), Furness (Morgan), Midland and southern counties 



II 



