THE TAPIR AND RHINOCEEOS. 193 



is another instance of the law laid down on p. 169, 

 that the hind extremities are more readily and 

 more frequently reduced than the fore limbs. 



In the tapir we have an animal from the Early 

 Tertiary period that has remained almost wholly 

 unchanged, one of those species which have been 

 called permanent, and which are more frequently 

 met with in the lower animal world. They do not 

 prove the invariability of the species, but prove 

 only that under certain circumstances the stability 

 of the species can be of an extremely long duration. 

 In the Miocene the genus is represented by several 

 good species. In the Middle Eocene, we have in its 

 place the Lophiodon, which is characterised by a 

 still greater simplicity of the ridges of the teeth, 

 and, as regards appearance generally, may have 

 been scarcely distinguishable from the tapir. The 

 European Lophiodonts naturally, in the first place, 

 lead over to the Indian caparisoned tapir. The 

 American ancestral line of the tapirs is more com- 

 plete. Two genera, Helaletes and Hyrachyus, 

 closely related to Lophiodon, belong to the Eocene. 

 They may be called tapir oid forms. At a somewhat 

 later period appears Lophiodon, one of the few 

 genera we have in common. Still more tapiroid 

 in form is the Miocene Tapiravus, which in the 



