SYSTEMATIC ZOOLOGY 267 



and is seldom to be recommended. There can be no doubt that badly 

 formed and inappropriate names have been a just cause of much of the 

 criticism of systematic work. The correcting of errors is always an un- 

 gracious task, especially where the errors are apparently trivial and 

 obviously unintentional, and this is particularly true in systematic 

 zoology. No reasonable person will, however, question the necessity of 

 it or refuse to accept the correction if it is justified. But in such work, 

 accuracy of statement, soundness of judgment, clearness of reasoning 

 and perfect courtesy are required to an unusual degree. These qualities 

 are, of course, essential for the best scientific work of any kind, but they 

 are particularly so in systematic zoology, where so much work is of an 

 elementary nature. The lack of one or more of them has depreciated 

 the value of many an elaborate monograph. On the other hand, their 

 presence does not alone guarantee the worth of a piece of zoological 

 research. And this suggests the second principle I desire to emphasize. 



To be of real ivorth and permanent value, the systematic study of 

 any group of animals must take into account, so far as they are hnown, 

 the pre- and post-natal development, the geological history and the 

 geographical distribution of the species which compose it. 



A systematic study of any group of animals which considers only 

 the adults, even if the morphology, physiology and habits are all taken 

 into account, can not be regarded as complete. Nature would indeed 

 be a puzzle and interrelationships a hopeless snarl, if the stages of de- 

 velopment were not discoverable or were meaningless. It is incredible 

 to me that any zoologist, who has examined the evidence at all, can 

 deny the existence of stages in both pre- and post-natal development or 

 question the fact that those stages have some meaning. And I am un- 

 able to believe that we can even approximate the true history of any 

 group of animals so long as those stages are ignored. Equally im- 

 portant is the paleontologieal evidence and to ignore it when it exists 

 in any appreciable amount is indefensible and may result in deplorable 

 error. For some reason the relationship of systematic zoology to geo- 

 graphical distribution has been more generally recognized than its 

 relation to paleontology, but it seems to rne obvious that in the diversi- 

 fication of the animal kingdom, the element of time has been fully as 

 important as that of space. In neither case, however, is it justifiable 

 to assume that quantity (of either time or space) is necessarily corre- 

 lated with specific qualities. Discontinuous distribution, either geolog- 

 ically or geographically, ought never to be regarded by itself as a dif- 

 ferential character. Either may be used as an additional character for 

 a group otherwise structurally distinguishable, but no species (or other 

 group) ought ever to be recognized whose identity can not be deter- 

 mined without knowing the locality or the geological horizon from 

 which it came. To act on any other principle can not fail to lead to 



