TRANSITIONS OF ORGANIC BEINGS. 155 



to exterminate the parent-forms and the intermediate links. 

 Consequently evidence of their former existence could be 

 found among fossil remains, which are preserved, as we shall 

 attempt to show in a future chapter, in an extremely imper- 

 fect and intermittent record. 



ON THE ORIGIN AND TRANSITION 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 strug- 

 gle for life, it is clear that each must be well adapted to 

 its place in nature. Look at the Mustela vision 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 dif- 

 ferent 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 disadvan- 

 tage, 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 difficulty in any partic- 

 ular case like that of the bat. 



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

 gradation from animals with their tails only slightly flat- 

 tened, and from others, as Sir J. Richardson has remarked, 

 with the posterior part of their bodies rather wide and with 

 the skin on their flanks rather full, to the so-called flying 

 squirrels ; and flying squirrels have their limbs and even th<* 

 base of the tail united by a broad expanse of skin, whiofc 

 serves as a parachute and allows them to glide through the 



