genera is an exaggeration, however inexpedient we may deem such genera to be. Wherever the number of species in a genus is, by the extension of our knowledge, so increased as to make the group unwieldy and more or less heterogeneous, it may for convenience be divided. "Whether such divisions are called genera or subgenera is again only a matter of expediency, but for my part I have never been able to see the merit of subgenera. If a group of species is not marked by sufficiently constant characters to make it recognizable, it is not entitled to a name, and if it is so marked, I fail to see why it should not be called a genus. I do not think the description of a tree would be made more lucid by an attempt to recognize sub-branchlets. It is true that the extensive use of subgenera would permit a corresponding decrease in generic names, but I do not think this would be any real advantage. We may as well face the fact that it is no longer possible for any one man, unless he be rarely gifted with the right sort of a memory, to know the principal genera of all classes of animals. Our knowledge of the animal kingdom has so expanded in the last thirty years, that even if a man specializes in the most elementary form of systematic zoology, he can not hope to have a comprehensive view of all known genera. No one will deny that this is to be regretted, but while the fault may be in part due to our systems of nomenclature, the chief blame must rest on nature and the curiosity of zoologists. The diversity of animal life and the zoologist's insatiable desire to continually increase our knowledge thereof are at the root of the trouble. It has been said that the general lack of interest in natural history among the people at large is due to our complex nomenclatural system. I doubt if interest in natural history is any less now than it has been in the past, but if it is I do not believe the fault is with our nomenclature. Granting, however, that it is, I do not see how the difficulty can be avoided. When we are told that the would-be naturalist knows a robin as Turdus migratorius and it is unfair to him to so divide Turdus that the robin has to be called by some other name, we can only reply that the inconvenience and annoyance of giving up the old name are obvious, but the progress of our knowledge of thrushes in their specific diversity has shown that the robin, when compared with the original species of the genus, is not a Turdus, and it is therefore inaccurate, to say the least, to continue to use that name. And in scientific work to be inaccurate is a more serious fault than to be annoying. The importance of accuracy in systematic work suggests a fourth principle which may be expressed as follows:
The value of a character for distinguishing species or higher groups depends chiefly on its constancy, and for indicating relationships within a group on its significance; in neither case is its conspicuousness anything more than a matter of convenience.