64 UNIVERSALITY OF DEGENERATIVE EVOLUTION 



later stage. In the primitive foot of the aminota, 

 the third toe is the longest, but among animals 

 which have become adapted to an arboreal life (fig. 

 32) the fourth toe preponderates, thus allowing of 

 a wider grasp, and the second (ii.) and the second 

 and third toes gradually degenerate (Arctocebus 

 calabarensis, Potto). A clear proof that this modi- 

 fication is due to adaptation to 

 arboreal life, lies in this same 

 tendency being exhibited by two 

 groups not closely allied to one 

 another the marsupials and the 

 lemurs. 



In a still more advanced stage 

 the phalanges of the second digit 

 ' disappear almost completely, and, 

 for a11 Poetical purposes, no 



of rertebrated Animals.) Among reptiles, chameleons 

 furnish a striking example of adaptation to climbing. 

 With them three digits are opposable to the other 

 two (figs. 33 and 34), instead of one being oppos- 

 able to the other four. To further promote this 

 opposability, there is a fusion of digits (syndactilism), 

 i.e. each set of digits is enclosed up to the nails 

 within a common integument. The result of this is 

 that the enclosed digits are no longer capable of 

 lateral movement, and the muscles have degenerated 

 in consequence. The wrist and tarsus also show 

 signs of partial degeneration. 



