i.] DARWINISM VERIFIED. 25 



any sub-kingdom are achieved by more or less con- 

 siderable modifications of a framework that in its 

 typical features is common to all. In embryonic 

 development the fins of the fish correspond with the 

 legs of reptiles and mammals, and with the legs and 

 wings of birds. To enable the bat to fly, no new 

 mechanism is invented, but an embryonal hand de- 

 velops into a wing by the elongation of its fingers 

 and the growth of a web-like skin between them. 



If we consider the most general features of the 

 geographical distribution and geological succession of 

 organisms, we find the evidence hardly less complete 

 and convincing. Generally speaking, the contem- 

 porary species found in any geographical area most 

 closely resemble the species that inhabited the same 

 area in former ages. Thus in the Miocene age 

 Australia abounded in marsupials, and marsupials 

 specifically different, though nearly allied to these, 

 make up to-day the greater part of the mammalian 

 fauna of Australia. There is no imaginable reason 

 why this should be so, unless the contemporary mar- 

 supials are descended from the earlier forms. It 

 cannot be urged that marsupials are better adapted 

 to the conditions of life in Australia than placental 

 mammals ; for the placental mammals lately intro- 

 duced there are already beginning to supplant and 



