MAMMALIA. 405 



to possess a chisel which would never wear out, and would 

 never become blunt, we might suppose that the handle of such 

 a tool would have in itself the means of secreting the iron 

 and the steel of which the blade is formed, of welding them 

 together, and of giving them at the same time the needful 

 polish and smoothness. And as such a gift would not partake 

 of the imperfections of human workmanship, the new material 

 would be deposited just in proportion as the old wore away, 

 and the temper of the chisel would be neither too hard nor too 

 soft, so that the edge would not be liable either to break or to 

 turn, but remain at all times in working order. Such in reality 

 is the mode of growth in the incisor teeth of the Rodentia 

 (Fig. 297). New matter is ever added at the base, the tooth 

 is ever growing, the enamel is deposited on the outer edge, 

 the softer or inner portions of the teeth wear away, and thus 

 the bevilled or sloping edge of these most efficient tools is 

 invariably preserved. 



Knowing these facts, we cannot examine the teeth of the 

 Rabbit, nor of the common Mouse, without being struck with 

 the amount of design they exhibit, the care for the wants of 

 the animal which they manifest, and the perfection in which 

 the continual growth compensates for the constant wearing 

 away. And these ideas become more vivid, and the convic- 

 tions to which they lead more indelible, if we observe what 

 takes place in cases where the usual order of things is interfered 

 with. "When," to use the words of Professor Owen, "by 

 accident an opposing incisor is lost, or when by the distorted 

 union of a broken jaw, the lower incisors no longer meet the 

 upper ones, as sometimes happens to a wounded Hare, the 

 incisors continue to grow until they project like the tusks of 

 the Elephant, and the extremities, in the poor animal's abortive 

 attempts to acquire food, also become pointed like tusks: fol- 

 lowing the curve prescribed to their growth by the form of 

 their socket, their points often return against some part of 

 the head, are pressed through the skin, then cause absorption 

 of the jaw-bone, and again enter the mouth, rendering masti- 

 cation impracticable, and causing death by starvation."* 



Hibernation, We have in this order several examples of 

 animals which hybernate, or pass the winter in a greater or 

 less complete state of torpidity. Thus the Marmot of the 

 Alps and Pyrenees dozes away the winter, until the sunshine 



* Odontography, p. 411, vide also plate 104, Fig. 5, in same work. 



