426 LAND ANIMALS 



of animals of the plains; the jumping animals with elongated hind 

 legs which have taken to dwelling in trees, such as the tree kangaroos, 

 Dendrolagus, of New Guinea and the lemur-like Tarsius of the East 

 Indies, appear to be secondarily arboreal. On the other hand, mam- 

 malian climbers tend to have the arms and pectoral girdle well de- 

 veloped. This is particularly noticeable among monkeys and their 

 allies. 



Parachutes have also been developed among diverse arboreal ani- 

 mals, and, flying animals excepted, are not found elsewhere. The 

 essential principle involved is the development of rigidly supported 

 membranes which enlarge the under surface of the body and permit 

 gliding flight. The lizards of the genus Draco have elongate lateral 

 ribs which support broad membranes. Parachuting mammals may 

 have extensive membranes connecting the legs. Such membranes have 

 been developed independently among the marsupials, among the squir- 

 rels, and most notably in the so-called flying lemur, Galeopithecus, 

 of the Malay region, in which they extend to the throat and to the 

 tip of the tail. In the ordinary squirrels, the bushy tails are flattened 

 and serve the same purpose. The presence of these gliding adaptations 

 in forest animals has led to the speculation that the flying habit origi- 

 nated among such vertebrates in the forest. 10 



A great number of predatory beetles whose relatives elsewhere are 

 ground-dwelling are arboreal in the Amazonian forests and have de- 

 veloped arboreal adaptations, particularly in foot structure. Thus a 

 tree-dwelling group, the Odontocheilae, has been developed among the 

 usually ground-inhabiting tiger beetles, Cicindelidae, whose larvae 

 burrow into twigs instead of into the soil. In the Amazonian forests 

 these are four times as abundant as are the tiger beetles proper. 11 

 Ants frequently establish themselves in trees and even make paper 

 nests there in the tropical rain-forest. Such forests furnish food and 

 shelter for leaf- and wood-feeding insects and their larvae, for snails 

 which range to the topmost branches, and in the Philippines, lay their 

 eggs in leaves folded together for their protection 12 (Fig. 117), and 

 for tree frogs (Hylidae), of which half the known species are from 

 the South American forests. Among birds, woodpeckers are infrequent 

 outside forest regions and are absent, for example, in Egypt. 13 Gal- 

 linaceous birds, ordinarily ground dwelling, are arboreal in the rain- 

 forests of South America. The curassow (Crax) and the hoatzin 

 (Opisthocomus) have retained the primitive bird foot with the hind 

 toe no higher than the rest. 



In these densely forested tropical regions, arboreal mammals pre- 

 dominate over ground forms. Of the 65 mammals in the island of Trini- 



