But let us glance at the subject through the medium of an example, and endeavour to realize what would be the consequence of that wholesale combination at which we must sooner or latter arrive, if genera are not to be upheld because they slowly merge into each other as we recede from their respective types. The immense department _Carabidae_, of the Coleoptera, is eminently a case in point. In the details of their oral organs the _whole_ of that family display (as I have elsewhere[82] remarked) so great a similarity _inter se_, or rather shade off into each other by such imperceptible gradations, that the _tendency_ which various clusters of them possess to assume modifications of form which attain their maximum only in successive centres of radiation, must oftentimes be regarded as _generic_, if we would not shut our eyes altogether to the natural collective masses into which the numerous species (however gradually) are, in the main, so manifestly distributed. It is possible indeed that, as our knowledge advances and new discoveries take place, we shall so far unite many of the consecutive nuclei which are now considered pretty clearly defined, that we shall be driven at last _either_ to accept the Linnaean genera only, or else the entire host of subsidiary ones (albeit perhaps in a secondary sense) which are, one by one, being expunged. And, since under the former contingency the _determination of species_ would become practically well nigh hopeless, it is far from unlikely that we shall eventually hail the latter as, after all (at any rate to a certain extent), the more convenient of the two. Look, for instance, at the great genus _Pterostichus_, which has nearly 200 representatives in Europe alone: true it is that its several sections (_Poe cilus_, _Argutor_, _Omaseus_, _Corax_, _Steropus_, _Platysma_, _Cophosus_, _Pterostichus_ proper, _Abax_, _Percus_, and _Molops_), although easily recognized in the mass, do unquestionably blend into each other; yet I believe that it has arisen from a too rigid promulgation of the generic theory that they have not been retained as separate. And this opinion may be rendered somewhat more plausible, from the knowledge that certain of the _Pterostichi_ (the Argutors, for instance) approach so closely, in their trophi, to _Calathus_, as to be hardly discernible from it; which latter genus is scarcely distinguishable (structurally) from _Pristonychus_,--a form which, in its turn, leads us on towards another type. Who would have imagined, again, some fifty years ago, that the widely distributed groups, _Calosoma_ and _Carabus_, were not thoroughly detached _inter se_? yet what naturalist _now_ can draw an exact line of demarcation between them? And so it is with numerous others, which it is needless to recall. The practical inference, however, from the whole, is this: _that if genera must be rejected because they are not homogeneous and isolated throughout, the only ones that will remain are those which