386 



THE AMERICAN NATURALIST [Vol. LI 



in this connection are the shape of certain ridges on the 

 skull, pads on the soles of the hind feet, the relative length 

 of the tail, the length of molar complexes, and the length 

 of the ears. 



It is significant to observe, how every field worker 

 who occupies himself specially with rats has his own 

 opinion about the relative importance of these different 

 points for the systematic classification of the animals, and 

 discovers very soon that the work done in museums does 

 not materially help him in his quest. 



In 1915 one of us was commissioned by the government 

 of the Netherlands to make a biological and zoological 

 study of the rat population of the Dutch East-Indian col- 

 onies, more especially of the island of Java, with the 

 ultimate object to find out what measures could be taken 

 to prevent the exceptionally serious damage to public 

 health and to agriculture caused by rats. Some pre- 

 liminary work on the subject had been done by medical 

 investigators and by a systematist working with pre- 

 served specimens in Holland. The systematic-zoological 

 work in Java was begun some years previously by Maj. 

 G. Ouwens, who is continuing the work after we were 

 obliged, for reasons of personal health, to leave the 

 tropics. 



Very soon after arrival we discovered how very little 

 the work done in European museums was to help us out in 

 the field. We are not systematic zoologists, and our rea- 

 sons for accepting the task lay in the promise the material 

 gave of throwing light on the question of species (in 

 which it has not disappointed us). Therefore the only 

 group of animals with which we have at all deeply con- 

 cerned ourselves with systematics is the rat, and we 

 would not be prepared to maintain that for other groups 

 the ordinary museum-zoology has so little value in giving 

 a conception of the relationship between species in nature. 

 Still, the study of rats from a semi-economical point of 

 view has certain advantages over purely scientific col- 

 lecting, as the material studied is very plentiful, and an 



