SYSTEMATIC ZOOLOGY 269 



genera is an exaggeration, however inexpedient we may deem such 

 genera to be. Wherever the number of species in a genus is, by the ex- 

 tension of our knowledge, so increased as to make the group un- 

 wieldy 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 correspond- 

 ing 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 pos- 

 sible 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 continu- 

 ally 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 nomencla- 

 ture. 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 migratorhis and it is unfair to him to so divide 

 Turdas 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 Tardus, 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 an- 

 noying. 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 any- 

 thing more than a matter of convenience. 



