LECTURE XVI. 457 



of cattle, horses, and pigs whicli now populate the exten- 

 sive tracts of South America, either in a wild or semi-domes- 

 ticated state, are, as is historically proved, the descendants of 

 some few imported specimens. The first generations, now 

 found in small numbers, had to struggle for their existence 

 in the foreign climate until the acchmatization process was 

 completed. Only after the race has been brought into har- 

 mony with surrounding media does it begin to multiply ra- 

 pidly ; only when it has become typical does the number in- 

 crease up to millions. But as to the transitional forms of the 

 few individuals of few generations, where are we to find them ? 

 Who is to disinter them from the soil ? The two species, the 

 original and the derived, are not apparently linked by an inter- 

 mediate form, as nobody can show them ; yet they did exist, 

 for the ti'ansition has taken place within historic times, and 

 is historically authenticated. 



Is the process difierent in wild animals ? Let us assume 

 that the transformation of the bear has taken place during the 

 glacial period, which, as we have shown, was only an in- 

 cident of the so-called diluvial period. There is no doubt 

 that most of the cave-bears perished by the advance of the ice, 

 which deprived them of their means of subsistence, and pre- 

 vented their emigration into other regions. But some few of 

 these animals were preserved; their successive generations 

 adapted themselves to the new conditions ; their wildness 

 diminished; their means of subsistence changed, and they 

 became smaller in size, until the change was effected and the 

 cave-bear transformed into the brown-bear which, now adapted 

 to the new external conditions, multiplied greatly. But the 

 transitional forms — the witnesses of the fierce struggle for 

 existence during changing conditions — must they not be far 

 less numerous than the typical species which form the terminal 

 points of this struggle ? 



Thus it will always be, if the surrounding media change 

 within a comparatively short time. The transitional forms re- 

 duced to a few individuals, will, among the number of typical 

 species adapted to external conditions, disappear, and it will 

 only be owing to a happy accident if, here and there, a speci- 

 men of them be found. 



