102 THE GENESIS OF SPECIES. [Chap. 



mals. If physical causes connected Avitli locality can abbre- 

 viate or anniliilate the tails of certain butterlhes, why niay 

 not similar causes produce an elbow-like j)roniinence on the 

 wings of other butterllies ? Tiiere are many such instances 

 of sinujltaneous modification. Mr. Darwin himself"* quotes 

 Mr. Gould as believing- tliat birds of the same species are 

 more briglitly colored under a clear alm{)sj)here, than when 

 living ou islands or near tlie coast. Mj-. Darwin also in- 

 forms us that AN'^ollaston is convinced that residence near 

 the sea affects the color of insects ; and linallj', that ^locpiin- 

 Tandon gives a list of plants which, when growing near the 

 sea-shore, have their leaves in some degree fleshy, though 

 not so elsewhere. In his work on " Animals and Plants 

 imder Domestication,"^" Mr. Darwin refers to M. Costa as 

 having (in JJuIl. de la Soc. Imp. iVAcclunat.^ tome viii., p. 

 351) stated that "young shells taken from tlie shores of 

 England and placed in the Mediterranean at once altered 

 tlieir manner of growth, and formed prominent diverging 

 rays like those on the shells of the proper Mediterranean 

 oyster ;''^ also to ^Mr. Meehan, as stating (Proc. Acad. JVat. 

 jSc. of Philadelphiaj Jan. 28, 1802) that " twenty-nine kinds 

 of American trees all diller from tlieir nearest Em-opean 

 allies in a similar manner, leaves less toothed, buds and 

 seeds smaller, fewer branchlets," etc. These are striking 

 examples indeed ! 



But cases of simultaneous and similar modifications 

 abound on all sides. Even as regards our own species 

 there is a very generally admitted opinion that a new type 

 has been developed in the United States, and this in al)out 

 a couple of centuries only, and in a vast nndtitude of in- 

 dividuals of diverse ancestry. The instances here given, 

 liowever, nujst sullicc, though more could easily be added. 



It may be well now to turn to grouj:)S presenting similar 

 variations, not through, but independently of, geographical 



» " Origin of Species," 5th edit., p. 166. ^^ Vol. ii., p. 280. 



