{439} <Footnote by the author.> I discuss this because if Quinarism true, I false. <The Quinary System is set forth in W. S. Macleay's _Horae Entomologicae_, 1821.> _On the kind of relation between distinct groups._ I have only one other remark on the affinities of organic beings; that is, when two quite distinct groups approach each other, the approach is _generally_ generic{440} and not special; I can explain this most easily by an example: of all Rodents the Bizcacha, by certain peculiarities in its reproductive system, approaches nearest to the Marsupials; of all Marsupials the Phascolomys, on the other hand, appears to approach in the form of its teeth and intestines nearest to the Rodents; but there is no special relation between these two genera{441}; the Bizcacha is no nearer related to the Phascolomys than to any other Marsupial in the points in which it approaches this division; nor again is the Phascolomys, in the points of structure in which it approaches the Rodents, any nearer related to the Bizcacha than to any other Rodent. Other examples might have been chosen, but I have given (from Waterhouse) this example as it illustrates another point, namely, the difficulty of determining what are analogical or adaptive and what real affinities; it seems that the teeth of the Phascolomys though _appearing closely_ to resemble those of a Rodent are found to be built on the Marsupial type; and it is thought that these teeth and consequently the intestines may have been adapted to the peculiar life of this animal and therefore may not show any real relation. The structure in the Bizcacha that connects it with the Marsupials does not seem a peculiarity related to its manner of life, and I imagine that no one would doubt that this shows a real affinity, though not more with any one Marsupial species than with another. The difficulty of determining what relations are real and what analogical is far from surprising when no one pretends to define the meaning of the term relation or the ulterior object of all classification. We shall immediately see on the theory of descent how it comes that there should be "real" and "analogical" affinities; and why the former alone should be of value in classification--difficulties which it would be I believe impossible to explain on the ordinary theory of separate creations. {440} In the corresponding passage in the _Origin_, Ed. i. p. 430, vi. p. 591, the term _general_ is used in place of _generic_, and seems a better expression. In the margin the author gives Waterhouse as his authority. {441} _Origin_, Ed. i. p. 430, vi. p. 591. _Classification of Races or Varieties._