Me introauchon of New Species, 187 



these plans have obtained in creation. Sometimes the series of 

 affinities can be well represented for a space by a direct pro- 

 gression from species to species or from group to group, but it 

 is generally found impossible so to continue. There constantly 

 occur two or more modifications of an organ or modifications of 

 two distinct organs, leading us on to two distinct series of spe- 

 cies, which at length differ so much from each other as to form 

 distinct genera or families. These are the parallel series or re- 

 presentative groups of naturalists, and they often occur in dif- 

 ferent countries, or are found fossil in different formations. 

 They are said to have an analogy to each other when they are so 

 far removed from their common antitype as to differ in many 

 important points of structure, while they still preserve a family 

 resemblance. We thus see how difficult it is to determine in 

 every case whether a given relation is an analogy or an affinity, for 

 it is evident that as we go back along the parallel or divergent 

 series, towards the common antitype, the analogy which existed 

 between the two groups becomes an affinity. We are also made 

 aware of the difficulty of arriving at a true classification, even in 

 a small and perfect group ; — in the actual state of nature it is 

 almost impossible, the species being so numerous and the modi- 

 fications of form and structure so varied, arising probably from 

 the immense number of species which have served as antitypes 

 for the existing species, and thus produced a complicated branch- 

 ing of the lines of affinity, as intricate as the twigs of a gnarled 

 oak or the vascular system of the human body. Again, if we 

 consider that we have only fragments of this vast system, the 

 stem and main branches being represented by extinct species of 

 which we have no knowledge, while a vast mass of limbs and 

 boughs and minute twigs and scattered leaves is what we have to 

 place in order, and determine the true position each originally 

 occupied with regard to the others, the whole difficulty of the 

 true Natural System of classification becomes apparent to us. 



We shall thus find ourselves obliged to reject all those systems 

 of classification which arrange species or groups in circles, as 

 well as those which fix a definite number for the divisions of each 

 group. The latter class have been very generally rejected by 

 naturalists, as contrary to nature, notwithstanding the ability 

 with which they have been advocated ; but the circular system 

 of affinities seems to have obtained a deeper hold, many eminent 

 naturalists having to some extent adopted it. AVe have, how- 

 ever, never been able to find a case in which the circle has been 

 closed by a direct and close affinity. In most cases a palpable 

 analogy has been substituted, in others the affinity is very 

 obscure or altogether doubtful. The complicated branching of 

 the lines of affinities in extensive groups must also afford great 



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