304 THE INDUCTIONS OF BIOLOGY. 



dom. Besides the subordination of groups and their general 

 distribution, some other facts are indicated. By the distances 

 of the great divisions from the general centre, are rudely- 

 symbolized their respective degrees of divergence from the 

 form of simple, undifferentiated organic matter; which we 

 may regard as their common source. Within each group, 

 the remoteness from the local centre represents, in a rough 

 way, the degree of departure from the general plan of the 

 group. And the distribution of the sub-groups within each 

 group, is in most cases such, that those which come nearest 

 to neighbouring groups, are tho^e which show the nearest 

 resemblances to them— in their analogies though not in their 

 homologies. JN^o diagram, however, can give a correct con- 

 ception. Even supposing the above diagram expressed the 

 relations of animals to one another as truly as they can be 

 expressed on a plane surface, (which of course it does not,) it 

 would still be inadequate. Such relations cannot be repre- 

 sented in space of two dimensions; but only in space of three 

 dimensions ''^ 



§ 101. While the classifications of botanists and zoologists 

 have become more and more natural in their arrangements, 

 there has grown up a certain artificiality in their abstract 

 nomenclature. When aggregating the smallest groups into 

 larger groups, and these into groups still larger, natur- 

 alists adopted certain general terms expressive of the suc- 

 cessively more comprehensive divisions ; and the habitual 

 use of these terms, needful for purposes of convenience, has 

 led to the tacit assumption that they answer to actualities in 

 ^Nature. It has been taken for granted that species, genera, 

 orders, and classes, are assemblages of definite values — that 

 every genus is the equivalent of every other genus, in respect 

 of its degree of distinctness ; and that orders are separated 

 by lines of demarcation that are as broad in one place as 

 another. Though this conviction is not a formulated one, 

 yet the disputes continually arising among naturalists on tha 



