No. 607] RATS AXD EVOLUTION 405 



coots, and whether the hybrids are fertile. It seems cer- 

 tainly significant that almost nowhere is the '*wirok" 

 population composed of Norvegicus animals as well as 

 Bandicoots, From one locality the people will report and 

 send in gray ''wiroks" (Norvegicus), from other locali- 

 ties they will send long-haired black ''wiroks" (Bandi- 

 coots). 



From the standpoint of a systematist, it may look as 

 if it were hardly more than a question of education 

 whether a man is going to follow Hossack and bring all 

 the animals of the Eattus group to one single, variable 

 species, Mus rattus, and will look upon the differences 

 between the three main species of this group as unin- 

 teresting variations, because he finds all kinds of inter- 

 mediates in a museum, or whether he is to take the oppo- 

 site view with certain English museum people, and give a 

 new species name to every couple or trio of rats of a not 

 hitherto described species. 



When we start with a drawerful of dried skins, it cer- 

 tainly is a matter of personal taste whether we will dis- 

 tribute the skins over three or ten or twenty smaller 

 drawers, each representing a species. Systematists may 

 quarrel about it, whether a difference in contour of a line 

 on a skull, or a different number of scales on the tail is or 

 is not sufficiently important to make a group deserve a 

 species name, or whether to call it a variety of some other 

 species. 



As soon as we have to deal practically with a group of 

 animals like the rats of Java, and have to consider the 

 economic importance of tree-rats to plantations, of house- 

 rats in connection with infections, and of field-rats as re- 

 gards crops, the museum kind of systematics very often 

 proves insufficient, and we have to begin the work anew 

 in another way. 



I remember that one day, among a batch of some ten or 

 eleven thousand rats caught on that day in a sugar plan- 

 tation, Ketangoengan, there were two with markedly 

 ruddy hue, two with very long tails, three house-rats 



