but it leaves for other zoologists to determine the means of transportation and the causes of the traveling. Briefly we may express the motive thus:
The purpose of systematic zoology is to determine the racial characteristics, and to set forth clearly the mutual interrelationships of animals.
The validity of this statement will not be affected, I think, by either the size of the group with which the systematist may deal, or the phase of the subject which specially interests him. It applies just as well to the man who specializes in a single genus as to him who attempts to comprehend a whole order or class. The only difference is that the smaller the group, the more the worker may hope to attain his purpose, at least to some degree. The larger the group the less is it possible for the purpose to be attained. Nor does it matter whether the systematist is especially interested in new species, or in the morphology or life histories of old ones, or in the geographical or geological distribution of animals. If his purpose is to determine more accurately the racial characteristics, or to make more clear the interrelationships, of the animals with which he deals, the value of his work as systematic zoology, at least so far as it is reliable, can not be questioned. And should the day ever dawn when it can be fairly said that the purpose of systematic zoology, here formulated, has been attained, we shall have, not merely a complete catalogue, but a complete history of the animal kingdom.
Having thus defined what seems to me the purpose of systematic zoology, I hope I may be pardoned if I attempt to formulate some of the principles which it seems to me ought to govern such work. And I may say at the outset that few inexperienced workers appreciate the difficulties involved. It is no uncommon thing to hear systematic work and workers severely criticized for the instability and uncertainty of their results. Such critics forget that nature is essentially unstable and that the fundamental difficulty of the systematist is the continual variation of the material with which he deals. No doubt much descriptive work has been poorly done and unfortunately it is true that in the past some systematists have ignored their predecessors and their colleagues. But at the present day descriptive work is, as a rule, well done and is often accompanied by most accurate figures, while ignoring the work of others is remarkably uncommon and is very rarely intentional. Nature, however, is as variable as ever and the best of descriptions and figures can not deal adequately with her marvelous diversity. Moreover, in addition to the inherent difficulty of variation in his material, the systematist has to face the even more exasperating difficulty of variation in human judgment. Not only do the judgments of his non-systematic colleagues differ from his own, but on any given point the best trained students of his particular group are quite likely to differ from him and
