CHAP. VI.] OF TRANSITIONAL VARIETIES. 129 



bution of closely allied or representative species, and likewise of 

 acknowledged varieties), exist in the intermediate zones in lesser 

 numbers than the varieties which they tend to connect. From 

 this cause alone the intermediate 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 varieties, 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 closely 

 together all the species of the same group, 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 attempt to show in a future 

 chapter, 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, could a land carnivorous 

 animal 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 there now exist carnivorous animals 

 presenting close intermediate grades from strictly terrestrial to 

 aquatic habits ; and as each exists by a struggle for life, it is clear 

 that each must be well adapted 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 the summer this animal dives for and preys on fish, but 

 during the long winter it leaves the frozen waters, and preys, like 

 other pole-cats, on mice and land animals. If a different case had 

 been taken, and it had been asked how an insectivorous quadruped 

 could possibly have been converted into a flying bat, the question 

 would have been far more difficult to answer. Yet I think such 

 difficulties have little weight. 



Here, as on other occasions, I lie under a heavy disadvantage, 

 for, out of the many striking cases which I have collected, I can 

 give only one or two instances of transitional habits and structures 

 in allied species ; and of diversified habits, either constant or 

 occasional, in the same species. And it seems to me that nothing 

 less than a long list of such cases is sufficient to lessen the diffi- 

 culty in any particular case like that of the bat. 



Look at the family of squirrels ; here we have the finest grada- 

 tion from animals with their tails only slightly flattened, and 



