Ciur. VI. TRANSITIONAL HABITS. 179 



diate varieties will be liable to accidental extermination ; 

 and during the process of further modification through 

 natural selection, they will almost certainly be beaten 

 and supplanted by the forms which they connect; for 

 these from existing in greater numbers will, in the 

 aggregate, present more variation, and thus be further 

 improved through natural selection and gain further 

 advantages. 



Lastly, looking not to any one time, but to all time, 

 if my theory be true, numberless intermediate varieties, 

 linking most closely all the species of the same group 

 together, must assuredly have existed ; but the very 

 process of natural selection constantly tends, as has been 

 so often remarked, to exterminate the parent-forms and 

 the intermediate links. Consequently evidence of their 

 former existence could be found only amongst fossil 

 remains, which are preserved, as we shall in a future 

 chapter attempt to show, in an extremely imperfect and 

 intermittent record. 



On the origin and transitions of organic beings with 

 peculiar habits and structure. — It has been asked by 

 the opponents of such views as I hold, how, for instance, 

 a land carnivorous animal could have been converted 

 into one with aquatic habits ; for how could the animal 

 in its transitional state have subsisted? It would be 

 easy to show that within the same group carnivorous 

 animals exist having every intermediate grade between 

 truly aquatic and strictly terrestrial habits ; and as 

 each exists by a struggle for life, it is clear that each is 

 well adapted in its habits to its place in nature. Look 

 at the Mustela vison of North America, which has 

 webbed feet and which resembles an otter in its fur, 

 short legs, and form of tail ; during summer this animal 

 dives for and preys on fish, but during the long winter 



