132 SPECIES NOT 



which, though a polecat in form, has webbed 

 feet; diving during summer for fish, and living 

 in the winter like other polecats. He also cites 

 the family of squirrels, which shew a gradual 

 development of wide posterior bodies and full 

 skins on their flanks, up to the flying squirrel, 

 and also the flying lemur, in which, however, 

 there are no links connecting it with the other 

 Lemuridce. These, Mr. Darwin considers, have 

 been lost, but he can see no difficulty in ima- 

 gining how "the membrane connected fingers and 

 fore-arm of the Galeopithecus might be greatly 

 lengthened by natural selection; and this, as far 

 as the organs of flight are concerned, would 

 convert it into a bat." 



In these surmises there is one thing which 

 must strike the reader as remarkable. Mr. Dar- 

 win admits that his "natural selection" can only 

 act for the good of the individual. It must, in 

 other words, be an advance in organization, so 

 as to give the changed species a superiority in 

 the "struggle for existence" with its weaker and 

 less fortunate brethren. But it will be remarked 

 that Mr. Darwin's instances of supposed trans- 

 mutation have a downward tendency in the scale 

 of organization. 



What a difference is there in the position of 

 the polecat and the fish! Yet, because Provi- 

 dence has thought right to give the former 

 means of getting its food in water, when it was 

 scarce on land, Mr. Darwin thinks this may il- 

 lustrate the transition between the mammal and 



