82 



NUTRITION. 



Still, they have one constant character, namely, their roots 

 are never simple, but double or triple, which not only 

 fixes them more firmly, but prevents them from being 

 driven into the jaw in the efforts of mastication. 



219. The harmony of organs already spoken of (22 -24) 

 is illustrated, in a most striking manner, by the study 

 of the teeth of the mammals, and especially of their molar 

 teeth. So constantly do they correspond with the struc- 

 ture of the other parts of the body, that a single molar 

 is sufficient not only to indicate the mode of life of the ani- 

 mal from which it was obtained, and to show whether it 

 fed on flesh or vegetables, but also to determine the particu- 

 lar group to which it belongs. Thus, those beasts of prey 

 which feed on insects, and which on that account have been 



Fig. 74. 



Fig. 76. Fig. 75. 



called Insectivora, such as the moles and bats, have the mo- 

 lars terminated by several sharp, conical points (Fig. 74), 

 so arranged that the elevations of one tooth fit exactly into 

 the depressions of the tooth opposite to it. In the true Car- 

 nivora (Fig. 75), on the contrary, the molars are com- 

 pressed laterally, so as to produce a sharp cutting edge ; 

 and they shut by the side of each other, like the blades of 

 scissors, thereby dividing the food with great facility. 



220. The same adaptation is observed in the teeth of 

 herbivorous animals. Those which chew the cud (rumi- 

 nants), many of the thick skinned animals (pachydermata), 



