108 HISTORY OF PHYSIOLOGY. 



clear and lively at its outset ; but, instead of reaching the great ocean 

 of the general truths of science, it is gradually spread abroad among 

 sands and deserts till its course can be traced nc longer. 



Hitherto, therefore, we must consider that we have had to tell the 

 story of the failures of physiological speculation. But of late there 

 have come into view and use among physiologists certain principles 

 which may be considered as peculiar to organized subjects ; and of which 

 the introduction forms a real advance in organical science. Though 

 these have hitherto been very imperfectly developed, we must endeavor 

 to exhibit, in some measure, their history and bearing. 



[2nd Ed.] [In order to show that I am not unaware how imperfect 

 the sketch given in this work is, as a History of Physiology, I may 

 refer to the further discussions on these subjects contained in the 

 Philosophy of the Inductive Sciences, Book ix. I have there (Chap, 

 ii.) noticed the successive Biological Hypotheses of the Mystical, the 

 latrocheinical, and latrornathematical Schools, the Vital-Fluid School, 

 and the Psychical School. I have (Chaps, iii., iv., v.) examined several 

 of the attempts which have been made to analyze the Idea of Life, to 

 classify Vital Functions, and to form Ideas of Separate Vital Forces. 

 I have considered in particular, the attempts to form a distinct concep- 

 tion of Assimilation and Secretion, of Generation, and of Voluntary 

 Motion ; and I have (Chap, vi.) further discussed the Idea of Final 

 Causes as employed in Biology.] 



CHAPTER VI. 



INTRODUCTION OF THE PRINCIPLE OF DEVELOPED AND METAMOR- 

 PHOSED SYMMETRY. 



Sect. 1. Vegetable Morphology. Gothe. De Candolle. 



DEPORE we proceed to consider the progress of principles which 

 -L' belong to animal and human life, such as have just been pointed at, 

 we must look round for such doctrines, if any such there be, as apply 

 alike to all organized beings, conscious or unconscious, fixed or loco- 

 motive ; to the laws which regulate vegetable as well as animal forms 

 and functions. Though we are very far from being able to present a 



