1 4 D EG EX ERA TIOX. 



horns to their offspring, and from these again the 

 cattle with the shortest horns would be selected by 

 the breeder for propagation, and so on through 

 several generations. In the end a very short-horned 

 generation would be obtained, differing greatly in 

 appearance from the cattle with which the breeder 

 started. 



Now we know of no facts which forbid us to sup- 

 pose that could a breeder continue his operations 

 indefinitely for any length of time — say for a few 

 million years — he could convert the short-horned 

 breed into a hornless breed ; that he could go on 

 and thicken the tail, could shorten the legs, get 

 rid of the hind limbs altogether by a series of in- 

 sensible gradations, and convert the race into forms 

 like the Sirenia, or sea-cows. But if he could do this, 

 you have only to give him a longer time still and there 

 is no obstacle remaining to the conversion, by the same 

 kind of process, of a polyp into a worm, or of a worm 

 into a fish, or even of a monkey into a man.i 



So far we have supposed the interference of a 

 breeder who selects and determines the varieties 

 which shall propagate themselves ; so far we have 



1 See Note B. 



