216 ARBOREAL MAN 



The South American monkeys are sometimes named 

 "four-handed," but some of them might, with equal 

 justice, be termed five-handed, so perfect is the specializa- 

 tion of the tail for all grasping and tactile functions. 

 Yet in this multiplicity of hands there is no evolutionary 

 gain. The true hands lose some of their perfections in 

 this sharing of their duties by other members, and the 

 animal becomes so much a perfected arboreal acrobat, 

 that advances in any other direction are wellnigh 

 impossible. 



With the other specialized results of arboreal habit 

 it is less easy to deal. That flying Mammals have 

 originated from arboreal Mammals is certain. The Indo- 

 Malayan and Australasian faunas teem with the repre- 

 sentatives of several orders which, having become 

 thoroughly arboreal, have gained some powers of aerial 

 flight. The particular ai^boreal specialization which 

 culminated in the power of flight is difficult to determine 

 w^th certainty, since comparative anatomy helps but 

 little, and paleontology not at all. There are, for instance, 

 no geological evidences of the types which linked the 

 Bats (already fully perfected in Eocene times) with any 

 other mammalian order from which thev were derived. 

 The curious Flying Lemur Gahopithecus volans (see 

 Fig. 80) has been regarded ]iy many anatomists as an 

 existing remnant of such a link, and Cheiromeles tor- 

 quatus, a Bornean Bat, possesses many of the characters 

 of a true tree-climber (see Fig. 81). But these creatures 

 hardly tell us how the habit of flight was acquired as an 

 arboreal specialization. It is natural to assume that an 

 arboreal animal which has learned to leap from branch 

 to branch in the astonishing manner evinced bv manv of 

 the Lemurs should progress in its special line by launching 

 itself into the air and increasing the lengths in its leaps 

 by gliding, or planing, on an outstretched membrane 

 derived from some part of its anatomy. There are many 

 leaping aerial gliders: we may instance the marsupial 



