138 Transitions of Organic Beings. Chap. VI. 



portions of a strictly continuous area, intermediate varieties will, it 

 is' probable, at first have been formed in the intermediate zones, but 

 they will generally have had a short duration. For these inter* 

 mediate varieties will, from reasons already assigned (namely from 

 what we know of the actual distribution of closely allied or repre- 

 sentative 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 inter- 

 mediate links. Consequently evidence of their former existence 

 >€ould be found only amongst fossil remains, which are preserved, as 

 we shall attempt to show in a future chapter, in an extremely im- 

 perfect and intermittent record. 



On the Origin and Transitions of Organic Beings with peculiar 

 Habits and Siructure.—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 Mustek vison of 

 North America, which has webbed feet, and which resembles an 

 otter m 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 



