110 THE FAUNA OF 
offering some analogy to the stiff tail of the wood- 
pecker (p. 47), which has the same function. 
We have already spoken of the Canadian porcupine 
(p. 43) in the taiga. This is represented in the 
tropical forests of Mexico and Brazil by the tree- 
porcupines of the genus Syntheres, which present 
some interesting adaptations to arboreal life. The tail 
is markedly prehensile, and the hind-foot is so inserted 
as to make it easy for the animals to grasp the branches. 
The great toe is absent, but its place is taken function- 
ally by a fleshy lobe which can be bent inwards so 
as to be partially opposed to the toes. The animals 
are stated not to drink, and probably do not descend 
voluntarily from the trees (see Fig. 30). 
We have already repeatedly emphasized the fact 
that ungulates in America are few, and that their place 
in nature is taken there by rodents; there is, therefore, 
nothing surprising in finding that the rodents called 
agutis (Dasyprocta) haunt the forests of Brazil and 
elsewhere, and have become adapted for life in the 
dense jungle. With their slender limbs and bodies 
they show a close, though entirely superficial, resem- 
blance to the chevrotains of South-East Asia. The paca 
(Coelogenys) has similar habits. 
With the Edentates we come to a primitive order, 
whose members have kept their hold in a world which 
has grown. beyond them either by retiring to the depths 
of the tropical forests, or by acquiring burrowing and 
concealed habits. In the forests of the Amazon occur 
the sloths, belonging to the genus Bradypus and 
Choloepus, perhaps the most truly arboreal of all 
mammals, for they are quite helpless if removed from 
the trees among which they pass their whole lives. 
The fact that;they possess practically no adaptation 
