102 THE GENESIS OF SPECIES. [CHAP. 



mals. If physical causes connected with locality can abbre- 

 viate or annihilate the tails of certain butterflies, why may 

 not similar causes produce an elbow-like prominence on the 

 wings of other butterflies ? There are many such instances 

 of simultaneous modification. Mr. Darwin himself 19 quotes 

 Mr. Gould as believing that birds of the same species are 

 more brightly colored under a clear atmosphere, than when 

 living on islands or near the coast. Mr. Darwin also in- 

 forms us that Wollaston is convinced that residence near 

 the sea affects the color of insects ; and finally, that Moquin- 

 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 u Animals and Plants 

 under Domestication," 20 Mr. Darwin refers to M. Costa as 

 having (in Bull, de la Soc. Imp. d'Acdimat., tome viii., p. 

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

 England and placed in the Mediterranean at once altered 

 their 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. Nat. 

 JSc. of Philadelphia, Jan. 28, 1862) that " twenty-nine kinds 

 of American trees all differ from their nearest European 

 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 about 

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

 dividuals of diverse ancestry. The instances here given, 

 however, must suffice, though more could easily be added. 



It may be well now to turn to groups presenting similar 

 variations, not through, but independently of, geographical 



19 Origin of Species," 5th edit., p. 166. 20 Vol. ii., p. 280. 



