68 PERPETUATION OF LIVING BEINGS 



the same thing occurring in the cases of the domestic 

 anim;ils dogs, for instance, and their offspring. In all 

 those cases of propagation and perpetuation, there seems 

 to be a tendency in the offspring to take the characters of 

 the parental organisms. To that tendency a special name 

 is given it is called Atavism ; it expresses this tendency 

 to revert to the ancestral type, and comes from the Latin 

 word alavus, ancestor. 



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

 before, one of the most marked and striking tendencies 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 powers 

 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 precisely 

 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 asexually ; 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 know 

 much about them ; but if we turn to that mode of per- 

 petuation which results from the sexual process, then we 

 find variation a perfectly constant occurrence, to a certain 

 extent ; and, indeed, I think that a certain amount of 

 variation from the primitive stock is the necessary result 

 of the n\cthod of sexual propagation itself ; for, inasmuch 

 as the thing propagated proceeds from two organisms of 



