:;ocS THH PLACl-: ()!• MIMICRY 



chalk, dark when toiiiul upon peat. XaturaHsts who 

 have had much experience of the species in its native 

 haunts assert tliat its habits are such as to render tliese 

 tints hicrhly protective. Careful experiments ^ have 

 proved tluit when nearly full-fed larvae are transferred 

 from chalk to a ver)- dark background, and ke[)t there 

 duriui^ the whole of the pupal period, the tints of the 

 resultin*^ moths are in no way affected. Unless the 

 imai^inal colours are determined by stimuli apj)lied still 

 earlier in the larval life — upon the whole an improl)able 

 conclusion — we can only suppose that the local colour- 

 harmony has been produced by the gradual destruction 

 throuiL^h many generations of the darker forms on chalk 

 and the paler ones upon peat, 8cc. 



I 2. T/ie Rccoit Pro(^7'cssive Darkejiino; of many Species 

 of MotJis in the LeineasJiire and Vo7'ks/iire J^istriet. — A 

 • •reat deal of evidence has been broucfht forward to show 

 that many moths in the neighbourhood of great centres 

 of population, and also in distant areas affected by their 

 smoke, have become very dift'erent in appearance from 

 what they were during the lives of the last generation of 

 naturalists and even within the memor)- of many still 

 living. The latest records on the subject are those of 

 Mr. G. T. Porritt,-' who does not himself accept the con- 

 clusion tliat the chancre has been caused b\- Natural 

 Selection. The smoke from the manufacturino- districts 

 of \'orkshire, driven by the prevalent S.^^^ wind, has 

 killed the lichen and rendered the tree trunks and 

 branches uniformly dark over a wide strip of country. 

 Their appearance has become utterly different, and the 

 pale variegated tints formerly borne by the moths in 

 question would now stand out with startling distinctness 

 upon them. It is of the utmost importance to gain the 

 fullest knowledge of the character of the struggle for 

 existence in these species, and to test the interpretation 

 founded on Natural Selection in every possible way ; 

 but the facts as they stand seem to raise an over- 

 whelming probability in favour of this explanation, which 



' Trans. Ent. Soc, Lond., 1892, pp. 453-8. 



' British Association, York. 1906, Report, p. 316. 



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