SYSTEMATIC ZOOLOGY 265 



but it leaves for other zoologists to determine the means of transporta- 

 tion and the causes of the traveling. Briefly we may express the motive 

 thus : 



The purpose of systematic zoology is to determine the racial charac- 

 teristics, 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 diffi- 

 culties 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, how- 

 ever, is as variable as ever and the best of descriptions and figures can 

 not deal adequately with her marvelous diversity. Moreover, in addi- 

 tion to the inherent difficulty of variation in his material, the system- 

 atist 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 



