1864.] DR. DAWSON ON CLASSIFICATION OF ANIMALS. 243 



2. So soon as we have ascertained the characters of a consid- 

 erable number of species, we find that in their nearest resembhmces 

 these do not constitute a linear series, but arrange themselves in 

 groups more or less separated from each other like constellations 

 in the heavens, and having relationships tending with more or 

 less force in different directions. This not only introduces com- 

 plexity into our systems, but renders it impossible to represent 

 them adequately in written or spoken discourse, or even by tables 

 or diagrams. We think and speak of things in series, but nature's 

 objects are not so arranged, but in groups radiating from each 

 other like the branches of a tree; and our imperfect modes of 

 thought and expression are severely tested in the attempt to 

 understand nature, or to convey ideas of classification to the minds 

 of others. 



3. The considerations above stated oblige us to enquire what 

 leading characters we may take as the principal thread of our 

 arrangement, so as to make this as natural as possible and at the 

 same time intelligible. It is simplest to take only one obvious 

 character, as if for example we were to arrange all animals accord- 

 ing to their colour or to the number of their limbs ; but the greater 

 the number of characters we can use, or the more completely we 

 can represent the aggregate of resemblances and differences the 

 more natural will our arrangement be, and consequently also the 

 more scientific and useful. 



In attempting to weigh the several characters presented by 

 any object, we find some that are of leading importance others 

 that are comparatively unimportant, though still not to be 

 neglected; and we find that some indicate grades of complexity 

 others are connected with adaptations to certain uses, and others 

 indicate plan of construction. Due weight must be given to all 

 these kinds and degrees of characters. It is perhaps in the proper 

 estimation and value of their relative importance and different 

 modes of application that the greatest failures have been made. 



Keeping in view these difficulties of the subject, we may now 

 proceed to the consideration of the more elementary of the groups 

 in which we arrange animals. 



2. The Species in Zoology. 



We cannot consider the animals with which we are familiar 

 without perceiving that they constitute kinds or Species, which do 

 not appear to graduate into each other, and which can be distin- 



