III.] INDEPENDENT SIMILARITIES OF STRUCTURE. 99 



the others before given, in which a common modification 

 of form or colour coexists with a certain geographical dis- 

 tribution quite independently of the destructive agencies 

 of animals. If physical causes connected with locality 

 can abbreviate or annihilate the tails of certain butter- 

 flies, 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 l quotes Mr. Gould as believing that birds 

 of the same species are more brightly coloured under a 

 clear atmosphere, than when living on islands or near the 

 coast. Mr. Darwin also informs us that Wollaston is con- 

 vinced that residence near the sea affects the colour 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 " Animals and Plants under Domestication," 2 

 Mr. Darwin refers to M. Costa as having (in Bull, de la Soc. 

 Imp. d'Acclimat. 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. A cad. Nat. Sc. of Philadelphia, Jan. 28, 

 1862) "that twenty kinds of American trees all differ 

 from their nearest European allies in a similar manner, 

 leaves less toothed, buds and seeds smaller, fewer branch- 

 lets," &c. These are indeed striking examples of con- 

 cordant modification ! 3 



i "Origin of Species," 5th edition, p. 1G6. 2 Vol. ii. p. 280. 



' ' Again, what, at first sight, can more accord with ' natural selection ' 

 than the fact that so many animals turn white in winter in Arctic regions ? 



H 2 [Those 



