( xciv ) 



ing such forms on the wing might, it is believed, avoid the 

 apparently dwarfed specimens, either because they afforded 

 less prospect of a sufficient meal, or (in accordance with a 

 suggestion of Mr, F. A. Heron) because, apparent size being a 

 correlative of distance, the attacker might be deluded into 

 supposing the black-bordered forms to be further away and so 

 less easily reached than the rest. 



" It is noticeable that in some cases of heavily-pigmented 

 wet-season forms, the under-side shows no corresponding 

 melanism, being often in fact far lighter in colour than the 

 under-side of the same species in the dry season. This exact 

 reversal of effect on the two surfaces is of itself a strong 

 argument against the supposed direct operation of meteor- 

 ological conditions in producing melanism. Such conditions, 

 as 1 have elsewhere urged, and as has been amply proved by 

 experiment, may act as a liberating stimulus ; but only rarely, 

 if at all, can they be looked upon as a direct cause of darkened 

 pigmentation. I would not entirely deny their direct effect 

 upon the individual, nor even that such direct effect may under 

 some circumstances reappear in the offspring. Weismann's 

 results with P. phlivas, Fischer's with Arctia caja, and others 

 on record (see Schneider-, " Einf Uhi-ung in die Deszendenz- 

 theorie," 1906, p. 113, etc.) seem to demonstrate the possibility 

 of such apparent transmission. But this phenomenon of the 

 diverse effect upon the two surfaces, together with the other 

 considerations already brought forward, appears to make 

 strongly against the hypothesis of a direct effect; and to 

 favour, as far as it goes, the view that such changes as these 

 are adaptive. 



" A further point of interest arises in connection with the 

 common absence of dark pigmentation on the under-side of wet- 

 season forms, even when the upper surface is strongly nielanic. 

 It is this : that on comparing the seasonal phases of such forms 

 we are often led to the conclusion that so far as the upper-side 

 is concerned the wet-season form is better protected, but with 

 regard to the lower-side the corresponding dry-season phase, 

 being cryptically coloured, has the advantage. This may mean 

 that the wet-season form requires more protection during flight, 

 and the dry -season form dui'ing repose ; and this again may 



