It is, nevertheless, often difficult to determine between the relationships of affinity and analogy, for groups even in close contiguity may also possess both. Thus, the normal _Ichneumones_ have their analogues in the _Ichneumones adsciti_, if the comparison be restricted to themselves, but these revert into the relationship of affinity when a comparison is instituted between them and the adjacent groups on the one side of the _Tenthredines_, or on the other of the _Aculeata_, with which, when a relationship presents itself, it is merely one of analogy. So, also, within the pentamerous _Coleoptera_ we have a relationship of analogy between the _Staphylinidæ_ and the _Histeridæ_, but it becomes one of affinity when it unites them within this section of the class.
Innumerable other instances might be given readily, but these will suffice to convey a notion of the relative meanings of the terms, ‘relation of affinity’ and ‘relation of analogy,’ which is all here aimed at.
The problem naturalists have to solve is, “What is the natural system?” We can clearly see that the systems adopted are not Nature’s, that they are essentially imperfect, and that the science, even with all the force of the intelligence that has been applied to it, is far from having attained perfection. It still awaits the master mind that shall cope with its difficulties, determine its intricacies, and, threading the labyrinth, guide his enthusiastic disciples into the adytum of the temple.
The subjects here brought under view admit of very considerable development, and of strictly didactic and methodical treatment. It has been my object only to gossip upon them, that I might stimulate curiosity to undertake systematic study, by showing how interesting it may become if earnestly pursued, being so fraught with instruction of large compass.
Works on natural history have divers objects in view, and may be intended either for popular and general distribution, or for special scientific purposes, and in each case the mode of treatment will materially differ. Many purposes may also be intended to be severally met in the strictly and rigidly scientific treatment. They may be either general methodical arrangements treated superficially, having no other design than to give a sort of bird’s-eye view of the subject in its wider distributions and broader landmarks, or they may treat of portions of the large subject more specially; again, they may constitute monographs of varying extent from a family to a genus; or they may comprise loose descriptions of new species of old and well-established genera; and some such, conjunctively with new species, establish likewise new genera, indicating, at the same time, their proximate position in the general series. The two latter classes are usually the appendages to voyages and travels in distant unexplored countries, or are the result of a careful collection of neglected tribes at home. Each, thus, with its special application has its special construction; but in the case of new species, I would strenuously counsel a full and complete description, and urge as imperative the construction of a specific character, formally framed to meet the condition of the science, based upon the precise antecedents and existing state of the genus to which such species belong.