24 TUSKS AND THEIR USES. 



purposes, and are thus in this respect analogous to the 

 antlers of many stags. In other instances, however — and 

 this in all the groups in -which they occur — they have 

 undergone a still further semi-monstrous development, 

 rendering them if not actually harmful, probably in some 

 cases inconvenient to their owners. Lastly, the independent 

 acquisition in closely allied or widely separated grou^JS of 

 mammals of tusks of very similar structvire and appearance, 

 shows how little reliance is to be placed on external 

 characters as indicative of relationshiji. 



