ch. -v.] THE LAW OF EVOLUTION. 349 



rearrangements of the matter of which organic "bodies are 

 composed. It remains to be shown how the rearrangements 

 of the motion retained by developing organisms exhibit the 

 same characteristics, and manifest themselves as differentia- 

 tions and integrations of function. All organic functions are 

 either molar motions of contractile muscles, or of circulatory 

 fluids, or else they are molecular motions in nerves, or in 

 secreting organs, or in assimilative tissues in general. To 

 show how these various motions become more specialized 

 and more consolidated as the organism is developed, let us 

 briefly reconsider the case of the alimentary canal, whose 

 structural modifications were lately described. The primitive 

 alimentary canal exhibits from end to end a tolerably uni- 

 form series of molar motions of constriction. But as the 

 canal becomes more heterogeneous, the molar movements in 

 its different parts simultaneously become more unlike one 

 another. While the waves of contraction and expansion 

 remain constant and moderate throughout the small in- 

 testine, they are replaced in the oesophagus by more violent 

 contractions and expansions that recur at longer rhythmical 

 intervals. In the stomach the mechanical undulations are 

 so much more powerful as to triturate the contained food, 

 and their rhythms are differently compounded ; while the 

 movements of the mouth are still further specialized in the 

 actions of biting and chewing. In the molecular motions 

 constituting secretion and absorption there is a similar 

 ' penalization. While absorption is confined chiefly to the 

 area covered by the lacteals, secretion is specialized in 

 various localities — in the salivary glands, in the gastric and 

 intestinal follicles, in the liver, and in the pancreas — and in 

 each place it has acquired a peculiar character. A like 

 increase in heterogeneity and definiteness marks the circu- 

 latory movements. In a slightly-evolved animal the nutri- 

 tive fluid, answering to blood, moves about here and there at 

 seeming random, its course being mainly determined by the 



