THE INTRODUCTION OF NEW SPECIES 



common antitype, then the series of affinities will be com- 

 pound, and can only be represented by a forked or many- 

 branched line. Now, all attempts at a Natural classification 

 and arrangement of organic beings show that both these plans 

 have obtained in creation. Sometimes the series of affinities 

 can be well represented for a space by a direct progression 

 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 

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

 form distinct genera or families. These are the parallel series 

 or representative groups of naturalists, and they often occur 

 in different countries, or are found fossil in different forma- 

 tions. 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 diffi- 

 culty 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 modifica- 

 tions of form and structure so varied, arising probably from 

 the immense number of species which have served as anti- 

 types for the existing species, and thus produced a compli- 

 cated branching 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 repre- 

 sented 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, so as to 

 determine the true position which 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 



