67 



losa, A. betidaria, C. duplaris, and M. liturata would be pro- 

 tective where the insects rest exposed, with the exception of 

 the dark form of M. liturata, which as it rests on the pine- 

 trunks is very efficiently protected, because it matches the 

 colour of the pine-bark extremely well ; the type can always 

 be easily seen if on the bark ; the insect, however, commonly 

 rests on the foliaged twigs. I have only seen one black A . 

 nebulosa at rest (or at all in nature), and I saw that at least 

 six yards away, across a brook, although it was worn." 



Mr. Mansbridge also says with reference to Pcedisca corti- 

 cana that it was very abundant in Delamere Forest this past 

 summer. The grey form was more difficult to see than 

 either the pale ochreous or black forms, thus showing that a 

 blackish insect resting on a Delamere tree-trunk is more 

 conspicuous than a grey one. Tephrosia biundularia, var. 

 delamerensis, he says, can be seen yards away. 



Knowsley, which is about ten miles north-east of Liver- 

 pool, is a smoky district, but not more so than around London, 

 as in Epping Forest, Highgate, Wimbledon Common, etc., 

 and here melanism is more prevalent than in the southern 

 woods, but not more so than in Delamere. 



A consideration of the facts concerning^, nebulosa does 

 not therefore appear to support the hypothesis that smoke, 

 or humidity, or the two combined, are responsible for the 

 change. 



A consideration of the distribution of the dark forms of 

 Xylophasia monoglypha shows similar contradictions. Like 

 A. nebulosa, dark forms occur in Delamere Forest, though 

 very sparingly. I have not met with them from North 

 Cornwall, but, unlike A. nebulosa, extremely dark forms are 

 found in Argyleshire and the Hebrides. It should be noted, 

 however, that A", monoglypha rests on tree-trunks less often 

 than A. nebulosa ; also such information as I have concern- 

 ing the distribution of melanic forms of Tephrosia biundularia 

 seems to me equally at variance with the hypothesis. 



On the other hand, in the West Riding of Yorkshire, of 

 course the trees and everything else are much blackened by 

 smoke, and here melanism in the case of moths that have 

 exposed resting habits is distinctly protective, yet Mr. 

 Mansbridge tells me that he cannot see that lepidoptera 

 from this district show much more appearance of melanism 

 than in Delamere and Knowsley. Polia chi is an exception, 

 the West Riding form being very different from those found 

 in the other places mentioned. Odontopera bidentata should 

 be noted as another exception. 



