CHAPTER X. 



RATS AND MICE. 



EVERY one is familiar with the common rat and the equally com- 

 mon house-mouse, but few realize that these pests have a host of 

 cousins, some of which are extremely grotesque, others remarkably 

 graceful, but one and all well worth studying. 



Rodentia is the largest mammalian order. It contains the 

 greatest number of species and individuals. All the members of the 

 order are characterized by the possession of chisel-like incisor teeth, 

 two in the upper and two in the lower jaw. There are neither canine 

 teeth nor premolars, a gap occurring between the two incisors and the 

 molars. 



In shape and size there is an infinite variation, though the largest 

 rodents are the Patagonian cavies, (about the size of a small sheep) 

 and the carpinchos (about the size of a small hog), also -South American 

 animals. 



The order is divided into numerous families, and in a short paper 

 like this one cannot hope to tackle them all. We will therefore con- 

 fine our remarks to the mouse-like rodents of North China. Here I 

 must ask the reader to allow me some laxity in my definition of 

 North China. Suppose we take the 33rd paralled of latitude as mark- 

 ing the dividing line between North and Central China. I am forced 

 to make this very arbitrary division in order to include certain species 

 which undoubtedly belong to the North China fauna, and yet whose 

 habitat is rather far south. The Zoologist is continually being faced 

 with these difficulties in determining the true boundaries of faunistic 

 areas, for species merge so imperceptibly! into each other, that it is 

 often quite impossible to state where one ends and the other begins. 



This division will give us plenty to think about, as will be seen 

 before I get to the end of this paper. 



Under this heading we have the jerboas (jumping or kangaroo 

 rats), the gerbils (sand rats), the hamsters (pouched rats), the voles 

 (field and water rats), the true rats and mice, and the molerats (under- 

 ground rats). 



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