588 NATURAL HISTORY. 



incisor, teeth. If we examine the jaws of a rat, we find that the two front 

 teeth in either jaw are always sharp and chisel-shaped. This is the result 

 of their structure. The hard enamel is all on the outer side of the tootji. 

 while the inner portion is composed of softer dentine ; so in use the softer 

 portion is worn away much faster than the hard, and in this way the cut- 

 ting edge is always kept sharp. "Were these teeth like those of man, and 

 exposed to the hard usage of those of a squirrel, or a beaver, they would 

 soon become worn down to the gums. But in the rodents this does not 

 occur ; the tooth is constantly growing at the base, and thus the loss is 

 continually made good. It occasionally happens that this growth does not 

 work for the benefit of the individual, no matter how good it is for the 

 race. If one of these teeth be broken or destroyed, the opposing tooth is 

 not worn away as it should be, but its growth continues just the same, and 

 so the tooth, curving as it grows, soon passes the mouth, and if it be 

 in the lower jaw, it may eventually grow around until it pierces the skull, 

 utterly barring the mouth, and eventually causing the death of the 

 unfortunate by starvation, even in the midst of plenty. Making the 

 proper changes in the words, the same account will apply to the teeth 

 of the upper jaw. 



The first of the rodents to be mentioned are the well-known hares and 

 rabbits, long-eared, jumping animals, mostly confined to the northern hem- 

 isphere. They are far from courageous animals ; they are rather the per- 

 sonification of timidity : they have no cunning and no means of defence ; 

 when danger comes, they must take to their legs or to their burrows. The 

 differences between hares and rabbits are very slight. In strict propriet}*, 

 the latter name is applicable only to the species of southern Europe, which, 

 in a state of domestication, has been distributed all over the world : all the 

 rest of the long series are hares. There is no necessity to describe all 

 these ; but a few must be mentioned at least by name. Among these are 

 the long-eared, long-legged jackass-rabbits of the plains, whose long leaps 

 and rapid gait are referred to in every book of travel. Then, too, the 

 ' Mollie cotton-tail ' of the "south, the wood-hare of the north, which 

 nowhere seems to have even a fraction of the cunning; and address of 

 the 'Brer Rabbit' of Uncle Remus. 



There is one aspect of rabbit-life which is interesting. Some of the 

 northern species are dark-colored in summer and white in winter. The 

 extent to which this process is carried varies considerably. In some the 

 sides and limbs retain a tawny shade ; while in others the whole annual 

 becomes a snowy white, excepting the tips of the ears, which remain black. 

 These hares which change in this way are called varying hares, and this 

 change in color is of the same nature as that found in the ptarmigan, the 



