68 STUDIES IN LIFE AND SENSE. 



proboscis of these animals may be regarded in the light of one of the 

 most useful as well as most interesting features of their organisation. 

 Its. use is not limited to the prehension of food (fig. 2, i, 2), however, 

 or even to the additional function of an organ of touch. Occa- 

 sionally, water is drawn up into the trunk, and is then squirted over 

 the body as from a flexible hose (fig. 2, s), thus serving as a kind 

 of shower-bath apparatus ; and stories have been recorded wherein 

 such a use of the proboscis has played a prominent part in the act 

 of elephantine revenge on some over-bold or offending human. 



The teeth of the elephantine race, as already remarked, form a 

 highly characteristic feature of their anatomy. In the mouth of a 

 higher quadruped, such as man, the bat, or ape, no less than four kinds 

 of teeth are represented. These are the front teeth or incisors, the 

 " eye-teeth " or canines, the premolars, and the molars or " grinders." 

 Furthermore, the growth of any individual tooth of ordinary kind 

 is of limited extent. As the roots of the "milk-teeth" disappear 

 by a natural process of absorption, and as these teeth fall out to 

 make room for their permanent successors of the second set, so the 

 latter teeth in their turn, when old age creeps upon us, fall out by 

 the decay and disappearance of their roots. Thus the growth of a 

 tooth, like that of the body at large, is confined to a certain period, 

 and by no means extends throughout the entire life of the individual. 

 But there are other teeth in the animal world which do not so termi- 

 nate their growth. The latter teeth continue to grow throughout the 

 entire life of their possessors. . They spring from what is known as 

 a " permanent pulp ; " a structure which, devoted to the original 

 formation of the tooth, continues to add to its substance as long as 

 life lasts. In the Rodent animals, such as the rats, mice, beavers, 

 porcupines, squirrels, and their allies, the front teeth grow from 

 " permanent pulps," the action of which supplies the loss of tooth- 

 substance which results from the inevitable tear and wear incurred in 

 the act of gnawing. So, also, in the walrus, the upper " eye-teeth " 

 grow from " permanent pulps," and develop into the well-known ivory 

 tusks of that animal ; and although the prominent " eye-teeth " of 

 the pigs do not increase throughout life, they yet exhibit a structure 

 nearly approaching the persistent type of tooth-growth. 



In the elephants, only two kinds of teeth are represented, these 

 being the incisors or front teeth, and the molars or grinders : whilst 

 the front teeth themselves only exist in the upper jaw. The incisors 

 grow from " permanent pulps," and hence they increase during the 

 whole life of the animal, or nearly so. A large pair of tusks may weigh 

 from 150 to 200 Ibs., and as regards structure they are found to con- 

 sist of dentine or " ivory " and of " cement ; " whilst the enamel, 

 which forms such a characteristic feature of ordinary teeth, may or 

 may not be represented. The tusks vary, according to Darwin, " in 



