154 EXPERIMENTAL EVOLUTION LECT. 



breed of bull-dog oxen has thriven and become a new 

 race. So in the San Paulo province of Brazil a new 

 breed of oxen suddenly appeared which is provided 

 with truly enormous horns, the breed of Franqueiros, 

 as they are called. The Mauchamp breed of sheep 

 owes its origin to a single lamb which was born in 

 1828 from merino parents, but whose wool, instead of 

 being curly like that of its parents, remained quite 

 smooth. This sudden variation is often met with, 

 and in France has been noticed in different herds. 



Other cases of the same sort might be quoted, 

 showing that, as some naturalists feel inclined to 

 believe, sudden variation is much less uncommon 

 than has been generally supposed. 



Having dealt at some length with the facts con- 

 cerning variability, we may briefly sum them up in 

 the statement that a certain degree of variability is 

 met with in every species, fossil or existing, animal or 

 vegetable, and that this variability is not found merely 

 in external characters, and does not affect only the 

 colour, dimensions, or integumentary appendages, but 

 that it extends also to the most deeply seated parts 

 such as the viscera and bones of animals, and reaches 

 even further, since physiological variability is merely 

 the external expression of physical and chemical 

 variations in the most intricate recesses of the various 

 parts which make up the organism. 



