THE LAW OF EVOLUTION CONCLUDED. 399 



development of functions. All active functions are either 

 sensible movements, as those produced by contractile or- 

 gans; or such insensible movements as those propagated 

 through the nerves; or such insensible movements as those 

 by which, in secreting organs, molecular re-arrangements 

 are effected, and new combinations of matter produced. 

 And what we have here to observe is, that during evolution, 

 functions, like structures, become more consolidated in- 

 dividually, as well as more combined with one another, at 

 the same time that they become more multiform and more 

 distinct. 



The nutritive juices in animals of low types, move hither 

 and thither through the tissues quite irregularly, as local 

 strains and pressures determine: in the absence of a dis- 

 tinguishable blood and a developed vascular system, there 

 is no definite circulation. But along with the structural 

 evolution which establishes a finished apparatus for dis- 

 tributing blood, there goes on the functional evolution 

 which establishes large and rapid movements of blood, 

 definite in their courses and definitely distinguished as 

 efferent and afferent, and that are heterogeneous not simply 

 in their directions but in their characters — being here di- 

 vided into gushes and there continuous. 



Instance, again, the way in which, accompanying the 

 structural differentiations and integrations of the aliment- 

 ary canal, there arise differentiations and integrations both 

 of its mechanical movements and its actions of a non-me- 

 chanical kind. Along an alimentary canal of a primitive 

 type, there pass, almost uniformly from end to end, waves of 

 constriction. But in a well-organized alimentary canal, 

 the waves of constriction are widely unlike at different 

 parts, in their kinds, strengths, and rapidities. In the 

 mouth they become movements of prehension and mastica- 

 tion — now occurring in quick succession and now ceasing 

 for hours. In the oesophagus these contractions, propulsive 

 in their office, and travelling with considerable speed, take 



