Chap. VI.] OP TRANSITIONAL VARIETIES. 215 



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 inter- 

 mediate varieties will be liable to accidental extermina- 

 tion; and during the process of further modification 

 through natural selection, they will almost certainly 

 be beaten and supplanted by the forms which they con- 

 nect; 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 pro- 

 cess 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 stniggle for life, it is clear that each must be well 

 16 



