RATS, MICE, AND VOLES 183 



classes. In spite of that, there is no more blameless 

 existence than that of this pretty rodent. You can 

 see all he does, for his habits are diurnal, instead of 

 nocturnal, like those of rats and mice. Watch him 

 as he swims from point to point of the bank ; if you 

 stand still, he will land almost at your feet and 

 nibble the stems of the succulent grasses, just as his 

 powerful relative the beaver once gnawed tree-stems 

 in this Itchen valley. The truth is, the water-rat is 

 not a rat (Mus) at all, but a vole (Arvicola), the only 

 true water-rat being found in Australia (Hydromys). 

 The voles may be distinguished from rats and mice 

 by several external marks, such as blunt instead of 

 pointed snouts, short instead of long tails, stumpy 

 ears and small eyes. But the most important differ- 

 ence is in the teeth ; the peculiar structure of its 

 molars, which have been pronounced the perfection 

 of molar dentition, ought to exonerate the water-vole 

 for ever from all suspicion of eating spawn, fish, or 

 other perquisites of greedy man. The twelve 

 molars have no roots, but grow on endlessly like 

 the incisors of other rodents, supplying the con- 

 stant wear caused by gnawing. They are tubes of 

 hard enamel, corrugated longitudinally, filled with 

 soft material. 



