286 FIRST PRINCIPLES OF NATURAL CLASSIFICATION. 



stant ; but the corallines assume an endless diversity of 

 form, although the general structure of the species is 

 essentially the same. Much experience, therefore, is 

 sometimes necessary to discriminate a species from a 

 variety : in general, however, a variety may be defined 

 as local or accidental, whose peculiarities are not per- 

 petuated in the next generation, and which cannot be 

 traced in more than a few individuals. It must be 

 again mentioned, nevertheless, that these observations 

 are applied only to animals in a state of nature ; since 

 it is well known that the greatest variation of form, 

 colour, and even of structure, have been produced by 

 long domestication. 



(34-7.) Having now sufficiently developed all those 

 principles of the system of nature with which we are 

 as yet acquainted, it follows that no arrangement of her 

 groups yet discovered can be natural, unless they exhibit 

 these principles in their details. It has frequently been 

 observed, and with great truth, that " a natural arrange- 

 ment will stand any test." But the test itself must 

 first of all be proved genuine. It is not a sufficient 

 test of our groups, that the individuals composing them 

 are placed in a circular series ; because hundreds of such 

 circles can be made out, the fallacy of which, did no 

 other test exist, can never be discovered. Neither is a 

 group sufficiently verified by making out its parallel 

 relations of analogy with another group; because, as all 

 contain the same denomination of types, we may happen 

 to compare a family with a genus, and, finding that 

 both have parallel analogies, may be led to fancy that 

 both are of equal value : both groups, indeed, may pos- 

 sibly be natural; but if we merely confine our analysis 

 to these, without investigating others which are con- 

 terminous, we may combine them falsely, and thus 

 throw a whole order into confusion. Parallel relations 

 must also be of a definite character, or the imagination 

 may be led astray : hence the necessity of verifying every 

 group, not only by the system of representation, but 

 also by the law of variation and succession of the pri- 



