THE PROBLEMS OF PHYSIOLOGY. 225 



more than very general and approximate interpretations of 

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

 nishes us 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 Physiological Evolution, 

 study the genesis of the different functions before we study 

 the inter-dependence that eventually arises among them and 

 constitutes physiological unity. 



