PAST PLUS THE PRESENT. 185 



iions of "accidental "( ?) variations, being prepotent over 

 long-assumed characters ; but in these cases the results were 

 partially aided by selection. 



Embryo more slightly modified than adult animal. — In the 

 womb there is a striking resemblance between the products 

 of very diverse animals at certain periods of their growth ; 

 and it is as growth advances that the differences become 

 definite enough for immediate recognition. In the young 

 animal, as in the foal or calf, the difference between animals 

 of different breeds is at birth but slight compared to those 

 which exist between the adult animals. In certain charac- 

 ters, such as the sexual, we find development only occurring 

 at a considerable interval from birth. This one instance of a 

 process continually in action may be formulated in the law of 

 development at corresponding periods of life. It is clear that 

 these two expressions of facts, in constant occurrence, are 

 somehow linked together, — the young animal being but a 

 continuation of the embryonic life under changed environ- 

 ment. When we consider that each animal is, in turn, the 

 sum of his past, plus his present, — that is, the force which 

 has originated, or which we recognize as vitality, has changes 

 impressed on it during each period of its history, it will be 

 perceived that the existing animal could not be exactly what 

 it is if any change had taken place in its previous condition. 

 Under the law of persistence of force, each concrete force is 

 just what it is through the changes which have been impressed 

 on its constituent units or parts. Any change of its unities, 

 at any one period of existence, produces a corresponding 

 change in the nature of the concrete force, whose expression 

 is the specific or individual life. We therefore have periods 

 of development; for, in the reproduction of an animal, the 

 forces come at first entirely from the past, and are modified in 

 turn by their entire past ; and these inherited forces after- 

 wards act against, as well as arc modified by, environment. 

 But to have a concrete force resembling another concrete 

 force, there must be a similarity between the causes which 

 have produced or developed. At each moment of the history 

 of an animal, changes arc being impressed, and the state of 

 the animal at this moment has been determined by its previous 

 state. We thus have a continual series of changes going on 



~ o o 

 24 



