388 



THE AMERICAN NATURALIST 



[Vol. LI 



ably different in a preserved state in respect to some 

 salient character, whereas in nature this very character 

 may be found to be so variable even within a small, 

 closely related family of animals, that it has no value 

 whatever for distinguishing two species. A case in point 

 is the presence or otherwise of flattened hairs, or spines 

 in the coat of rats. On the other hand, it may happen that 

 two species, if once they are dried and preserved in a 

 museum, present no, or, no appreciable, differences, 

 whereas in reality, these two species may be found to 

 differ very definitely biologically. As an illustration we 

 may cite the case of the field-rat and the tree-rat in Java. 



The easiest way out of the difficulty is the one 

 taken by a great many zoologists, working through large 

 collections of animals in museums namely, to give a new 

 species-name to every animal which differs markedly 

 from other described species, and which as yet goes with- 

 out a name. 



But if one wants to go deeper into the subject, if one 

 wants to know whether these species of the drawer have 

 their counterpart in as many species in the forest and 

 field, the task becomes more difficult and even hopeless for 

 a great many investigators. As soon as specialists take 

 in hand some group or other, it is very soon obvious that 

 the task of finding out just how many species they are 

 dealing with and how they differ is very much more com- 

 plicated than it looked when studying the collections in a 

 museum, however well stocked. In treating rat material 

 from a zoological-systematical standpoint, a number of 

 problems confront the investigator from the very outset, 

 and he must try to find his own solutions. Every inves- 

 tigator treats the material in his own way, and where one 

 man makes fifty species, some other man will make two 

 species out of the same material. It is evident, that if the 

 term "species" means anytliing at all, it must livpo- 

 thetically ])o possible to divide tlio material into a I'ix-ed 



he chiefly 



