400 THE LAW OF EVOLUTION CONCLUDED. 



place at intervals during eating, and then do not take place 

 till the next meal. In the stomach another modification of 

 this originally uniform action occurs: the muscular con- 

 strictions are powerful, and continue during the long pe- 

 riods that the stomach contains food. Throughout the upper 

 intestines, again, a further difference shows itself the 

 waves travel along without cessation but are relatively mod- 

 erate. Finally, in the rectum this rhythm departs in an- 

 other way from the common type: quiescence lasting for 

 many hours, is followed by a series of strong contractions. 

 Meanwhile, the essential actions which these movements aid, 

 have been growing more definitely heterogeneous. Secre- 

 tion and absorption are no longer carried on in much the 

 same way from end to end of the tube ; but the general func- 

 tion divides into various subordinate functions. The sol- 

 vents and ferments furnished by the coats of the canal and 

 the appended glands, become widely unlike at upper, mid- 

 dle, and lower parts of the canal; implying different kinds 

 of molecular changes. Here the process is mainly secretory, 

 there it is mainly absorbent, while in other places, as in 

 the oesophagus, neither secretion nor absorption takes place 

 to any appreciable extent. While these and 



other internal motions, sensible and insensible, are being 

 rendered more various, and severally more consolidated and 

 distinct, there is advancing the integration by which they 

 are united into local groups of motions and a combined sys- 

 tem of motions. While the function of alimentation sub- 

 divides, its sub-divisions become co-ordinated, so that mus- 

 cular and secretory actions go on in concert, and so that 

 excitement of one part of the canal sets up excitement 

 of the rest. Moreover, the whole alimentary function, 

 while it supplies matter for the circulatory and respira- 

 tory functions, becomes so integrated with them that it 

 cannot for a moment go on without them. And, as evolu- 

 tion advances, all three of these fundamental functions 

 fall into greater subordination to the nervous functions^- 



