X INTRODUCTION. 



nature of living beings is two-fold — Morpho- 

 logical and Physiological. 



The relations of living beings may, in like 

 manner, be viewed under two distinct aspects, 

 namely : 



1. Their relations to one another, i. e. their 

 mutual or subjective relations. 



2. Their relations to the conditions in which 

 they are placed, i. e. their external or objective 

 relations. 



We endeavour to express our appreciation of 

 the first kind of relations in our attempts to frame 

 a natural Classification; whilst our knowledge of 

 the second is involved in a statement of those 

 facts from which, it is hoped, we may be enabled 

 to deduce the laws of Distribution, 



But what are the characters of living bemgs, 

 and how may they be distinguished from the 

 members of the inorganic world ? This question 

 presents itself for solution at the outset of our 

 inquiries, since it is desirable to determine the 

 limits of the region which we have undertaken to 

 explore. 



To frame a definition of life, is, however, im- 

 possible, this agent being only known to us by its 

 effects.^ When the so-called vital principle is 

 associated with matter, as in a living body, we 

 invariably observe that it confers upon the latter 

 a tendency to pass through a series of changes. 



