182 HISTORY OF PHYSIOLOGY. 



self made a large advance with it ; and it was because he was so poised 

 by the vast mass of his knowledge, so temperate in his love of doubt- 

 ful generalizations, that he was not swept on in the wilder part of the 

 stream. To such a charge, moderate reformers, who appreciate the 

 value of the good which exists, though they try to make it better, and 

 who know the knowledge, thoughtfulness, and caution, which are need- 

 ful in such a task, are naturally exposed. For us, who can only decide 

 on such a subject by the general analogies of the history of science, 

 it may suffice to say, that it appears doubtful whether the fundamental 

 conceptions of affinity, analogy, transition, and developement, have yet 

 been fixed in the minds of physiologists with sufficient firmness and 

 clearness, or unfolded with sufficient consistency and generality, to 

 make it likely that any great additional step of this kind can for some 

 time be made. 



We have here considered the doctrine of the identity of the seem- 

 ingly various types of animal structure, as an attempt to extend the 

 correspondencies which were the basis of Cuvier's division of the ani- 

 mal kingdom. But this doctrine has been put forward in another 

 point of view, as the antithesis to the doctrine of final causes. This 

 question is so important a one, that we cannot help attempting to give 

 some view of its state and bearings. 



CHAPTER VIII. 



THE DOCTRINE OF FINAL CAUSES IN PHYSIOLOGY. 



Sect. 1. Assertion of the Principle of Unity of Plan. 



E have repeatedly seen, in the course of our historical view of 

 Physiology, that those who have studied the structure of animals 

 and plants, have had a conviction forced upon them, that the organs 

 are constructed and combined in subservience to the life and functions 

 of the whole. The parts have a purpose, as well as a law ; we can 

 trace Final Causes, as well as Laws of Causation. This principle is 

 peculiar to physiology ; and it might naturally be expected that, in the 

 progress of the science, it would come under special consideration. 

 This accordingly has happened ; and the principle has been drawn 



