DEPENDENCE ON ASSOCIATION. 81 



organisms has its source in the food and environ- 

 ment, — except perhaps those primitive forces whose 

 interaction produces the simplest form of life, and 

 which may perhaps be considered as somehow 

 resident in living matter, or as properties of the 

 component elements. But no life can continue, 

 and no life does exist as we know it, without the 

 constant action of forces from the environment. 



The energy or combination of forces residing in 

 the embryonic germ, and controlling and determining 

 its development, may seem to be an exception to the 

 above general statement. But the whole history 

 of evolution, so far as it has been interpreted, tells 

 us that this combination of forces, or this potential 

 energy, has been acquired gradually through long 

 ages. The particular form of potential energy which 

 exists in a chicken's egg, and determines into what 

 it shall develop, did not exist in any living thing 

 during the palasozoic era. It must have been ac- 

 quired by the action of environment upon certain 

 organisms. 



In the previous chapter we have seen that forces 

 act upon living matter chiefly through the nervous 

 system, or where such a structure is absent, the 

 forces affect what we recognise as the nervous 

 state of the organism. We have seen that where 

 the forces of the environment act upon the organs 



