118 LIFE IN NATURE. 



were, of greatest energy. It is only by duly marking 

 these, that the effect of mechanical conditions in 

 determining form can be appreciated." And again : 

 " If it should be remarked that there exist in de- 

 veloping structures certain definite modes or opera- 

 tions of force, such as attractions or repulsions in 

 particular directions, which serve to determine the 

 form assumed, apart from any influence of visible 

 mechanical conditions, this is willingly admitted to 

 be true. The law suggested does not contravene, 

 but rests upon these phenomena. They may be re- 

 garded in two ways: either as instances of those 

 local manifestations of growth before referred to, and 

 which are presupposed as the foundation on which 

 the law is based ; or, perhaps, more properly, they 

 may be themselves considered as coming within its 

 scope. In so far as these changes consist in the 

 motion of particles, the law of least resistance may 

 be asserted of them, or at least cannot be denied. 

 Such molecular changes indeed form no part of the 

 evidence on which the proposition can be based ; inas- 

 much as the nature of the process and all its conditions 

 are as yet beyond our investigation. But that in so far 



