16 ARBOREAL IVIAN 



have a bearing upon the present study. To these hop- 

 ping animals we will return. 



We will now come back to our primitive Mammal with 

 its four mobile limbs, and picture it taking, not to a ter- 

 restrial, but to an arboreal life. I imagine that the first 

 stages of this advance could be pictured as being built 

 upon the ability the animal already possessed of sur- 

 mounting such obstacles as chanced to lie in its terres- 

 trial path. The ability which such a primitive Mammal 

 would have for climbing might perhaps be gauged by 

 having regard for that skill in clambering which is mani- 

 fested in the tailed Amphibians, a skill which we must 

 remember develops within the limits of their own Phylum 

 (in the Tree Frogs) into perhaps the most perfected tree- 

 climbing displayed in the Vertebrate series. It may 

 seem a long way to go back when attempting to unravel 

 the influences of tree-climbing among the Primates, to 

 appeal to the clambering activities of the w^ater-newt. 

 And yet the anatomical condition of the limbs of Man 

 demands a shifting backward of the inquiry to some such 

 stage as this. I believe that the truest picture of the 

 evolution of Primate climbing starts with such a scene 

 as we are depicting now. The method of this amphibian 

 or reptilian clambering must be appreciated, for, as we 

 shall see, climbing may be conducted in several different 

 ways ; and the particular method practised by any animal 

 may serve to date the evolutionary stage at which the 

 habit was adopted. An Amphibian, or unspecialized 

 Reptile, ascends an obstacle by clambering up; its feet 

 are applied to the surface of the obstacle up which it 

 clambers. It makes no attempt to obtain a grip b}^ nails 

 or claws, but it trusts merely to the apposition of its feet 

 to the surface to which it clings, and when this fails the 

 animal falls. 



Two points must be especially noticed. As its progress 

 continues, it repeatedly reaches ahead with one or other 

 of its fore-limbs for a new hold, and whilst doing this its 



