30 THE POPULAR SCIENCE MONTHLY. 



* 



THE DIFFERENCES BETWEEN ANIMALS AND PLANTS. 



By W. K. brooks. 



THE original investigator of Nature soon learns by constant expe- 

 rience that descriptions or even drawings, however correct, do not 

 exactly represent the objects themselves, but are imperfect and ideal 

 abstractions. This is true, to a greater or less extent, of every draw- 

 ing of the simplest organ or tissue, and of every description of a species 

 or genus of animals or plants; but it is especially and most emphati- 

 cally true of all attempts at definitions of the larger and more compre- 

 hensive groups of organisms. 



A definition of such a group as an order or class of animals, attempt- 

 ing as it does to state in a few words the characteristics which are com- 

 mon to all the forms included, is necessarily abstract, and may not, in 

 fact cannot, be exactly embodied in any one individual of the whole 

 group. Then, too, certain characteristics which are exhibited by only 

 one or two aberrant forms, and are accordingly not characteristic of 

 the group as a whole, may be omitted from the definition^ although 

 they furnish the clew to the relationship with allied groups, and are 

 therefore of the utmost importance. An illustration which is not 

 drawn from the organic world may make this more evident. The fact 

 that printed books have followed and are a perfected form of the 

 parchment manuscripts of the middle ages is shown by the ornamental 

 initial letters, imitations of the illuminated letters of the manuscripts, 

 which are placed at the heads of the chapters of a few books. Not- 

 withstanding their significance, these initial letters would not find a 

 place in any definition or general description of a modern book. 



As a consequence of this inevitable lack of agreement between 

 natural objects and their definitions, all knowledge of Nature is of very 

 little value unless it is based upon a direct personal acquaintance with 

 Nature itself. How different, for instance, will be that conception of 

 such a group as the Coelenterata, which is formed by the study of a 

 short, definite, verbal description, from the idea in the mind of the 

 student whose knowledge of the group as a whole has been acquired 

 gradually by the study and comparison of the various forms of life 

 which it includes ! 



Definitions are valuable and indispensable aids to study, and, as long 

 as their necessary lack of agreement with the reality is kept in mind, 

 they can do no harm ; but the history of science warns us to be con- 

 stantly on our guard, lest distinctions which seem to be sharp and ab- 

 solute, when stated in words, come to be regarded as having as real an 

 existence in Nature as in words, and we thus come, in the words of 

 Bacon, to exchange "things for words, reason for insanity, and the 

 world for a fable." 



