THE PROBLEMS OF PHYSIOLOGY. 



225 



more than very general and approximate interpretations of 

 this kind are possible. If the hypothesis of Evolution fur- 

 nishes ns with a rude conception of the way in which the 

 more conspicuous and important differentiations of functions 

 have arisen, it is as much as can be expected. 



§ 267. It will be best, for brevity and clearness, to deal 

 with these physiological problems as we dealt with the 

 morphological ones — to carry on the inductive statement and 

 the deductive interpretation hand-in-hand: so disposing 

 of each general truth before passing to the next. Treating 

 separately vegetal organisms and animal organisms, we will 

 in each kingdom consider: — first, the physiological differentia- 

 tions and accompanying changes of structure that arise be- 

 tween outer tissues and inner tissues ; next, those that arise 

 between different parts of the outer tissues ; and, finally, 

 those that arise between different parts of the inner tissues. 

 What little has to be said concerning physiological integra- 

 tion must come last. For though, in tracing up Mor- 

 phological Evolution, we have to study those processes of 

 integration by which organic aggregates are formed, before 

 studying the differentiations that arise among their parts ; 

 we must, contrariwise, in tracing up Plrysiological Evolution, 

 study the genesis of the different functions before we study 

 the inter-dependence that eventually arises among them and 

 constitutes physiological unity. 



