240 PHYSIOLOGICAL DEVELOPMENT. 



foregoing pages this truth has been made abundantly mani- 

 fest. Here we are obliged to recognize the inter-dependence 

 still more distinctly; for the phenomena of function cannot 

 even be conceived without direct and perpetual consciousness 

 of the phenomena of structure. Though the subject-matter 

 of Physiology is as broadly distinguished from the subject- 

 matter of Morphology as motion is from matter ; yet, just as 

 the laws of motion cannot be known apart from some matter 

 moved, so there can be no knowledge of function without a 

 knowledge of some structure as performing function. 



Much more than this is obvious. The study of functions, 

 considered from our present point of view as arising by 

 Evolution, must be carried on mainly by the study of the 

 correlative structures. Doubtless, by experimenting on the 

 organisms which are growing and moving around us, we may 

 ascertain the connexions existing among certain of their 

 actions, while we have little or no knowledge of the special 

 parts concerned in those actions. In a living animal that 

 can be conveniently kept under observation, we may learn 

 the way in which conspicuous functions vary together — how 

 the rate of a man's pulse increases with the amount of 

 muscular exertion he is undergoing; or how a horse's 

 rapidity of breathing is in part dependent on his speed. 

 But though observations of 'this order are indispensable — 

 though by accumulation and comparison of such observations 

 we learn which parts perform which functions — though such 

 observations, prosecuted so as to disclose the actions of all 

 parts under all circumstances, constitute, when properly 

 generalized and co-ordinated, what is commonly understood 

 as Physiology; yet such observations help us but a little 

 way towards learning how functions came to be established 

 and specialized. We have next to no power of tracing up 

 the genesis of a function considered purely as a function — no 

 opportunity of observing the progressively-increasing quan- 

 tities of a given action that have arisen in any order of 

 organisms. In nearly all cases we are able only to show 



