DIFFICULTIES OF THE THEORY 241 



from what we know of the actual distribution of closely 

 allied or representative species, and likewise of acknowl- 

 edged 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 nat- 

 ural selection constantly tends, as has been so often re- 

 marked, to exterminate the parent-forms and the interme- 

 diate links. Consequently evidence of their former existence 

 could be found only among fossil remains, which are pre- 

 served, 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 asuecl 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 sub- 

 sisted ? 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 



— SCIENCK — 11 



