FUNCTION. 161 



from homogeneity to heterogeneity of structure, it is needful 

 to contemplate it under a converse aspect. Standing alone, 

 the above exposition conveys both an inadequate and an 

 erroneous idea. The divisions and subdivisions of function, 

 becoming definite as they become multiplied, do not lead to 

 a more and more complete independence of functions ; as 

 they would do were the process nothing beyond that just de- 

 scribed ; but by a simultaneous process they are rendered 

 more mutually dependent. While in one respect they are 

 separating from each other, they are in another respect com- 

 bining with each other. At the same time that they are 

 bein^ differentiated, they are also being integrated. Some 

 illustrations will make this plain. 



In animals which display little beyond the primary dif- 

 ferentiation of functions, the activity of that part which 

 absorbs nutriment or accumulates force, is not immediately 

 bound up with the activity of that part which, in producing 

 motion, expends force. In the higher animals, however, the 

 performance of the alimentary functions depends on the per- 

 formance of various muscular and nervous functions. Masti- 

 cation and swallowing are nervo-muscular acts ; the ryth- 

 mical contractions of the stomach and the allied vermicular 

 motions of the intestines, result from the stimulation of cer- 

 tain muscular coats by the nerve- fibres distributed through 

 them ; the secretion of the several digestive fluids by their 

 respective glands, is due to nervous excitation of them ; and 

 digestion, besides requiring these special aids, is not properly 

 performed in the absence of a continuous discharge of energy 

 from the great nervous centres. Again, the function 



of transferring nutriment or latent force, from part to part, 

 though at first not closely connected with the other functions, 

 eventually becomes so. The short contractile tube which 

 propels backwards and forwards the crude dilute blood con- 

 tained in the perivisceral cavity of an inferior mollusc, is 

 neither structurally nor functionally much entangled with 



the creature's other organs. But on passing upwards through 

 8 



