86 THE PERPETUATION OF LIVING BEINGS, 



black-board that you may remember it — it is called 

 Atavism; it expresses this tendency to revert to the 

 ancestral type, and comes from the Latin word atavus, 

 ancestor. 



Well, this Atavism which I shall speak of, is, as I 

 said before, one of the most marked and striking ten- 

 dencies of organic beings ; but, side by side with this 

 hereditary tendency, there is an equally distinct and 

 remarkable tendency to variation. The tendency to 

 reproduce the original stock has, as it were, its limits, 

 and side by side with it there is a tendency to vary in 

 certain directions, as if there were two opposing pow- 

 ers working upon the organic being, one tending to 

 take it in a straight line, and the other tending to make 

 it diverge from that straight line, first to one side and 

 then to the other. 



So that you see these two tendencies need not pre- 

 cisely contradict one another, as the ultimate result 

 may not always be very remote from what would have 

 been the case if the line had been quite straight. 



This tendency to variation is less marked in that 

 mode of propagation which takes place asexual ly ; it is 

 in that mode that the minor characters of animal and 

 vegetable structures are most completely preserved. 

 Still, it will happen sometimes, that the gardener, 

 when he has planted a cutting of some favourite plant, 

 will find, contrary to his expectation, that the slip 

 grows up a little different from the primitive stock — 

 that it produces flowers of a different colour or make, 

 or some deviation in one way or another. This is what 

 is called the " sporting " of plants. 



In animals the phenomena of asexual propagation 

 are so obscure, that at present we cannot be said to 



