VII HABITS OF KOALA 143 
The tooth formula of the genus is 13 C4 Pmi M,+,. The 
additional lower molar seems to be exceptional, and has been found 
in one specimen only. 
In the alimentary tract the most remarkable structure is the 
large intestine, which is very capacious for the first 28 inches or 
so of its course. This section of the colon is lined with rugae 
precisely like those which are found in the caecum. These folds, 
which at first are some twelve in number, fuse lower down, and 
by the time that the colon approaches the external orifice are 
reduced to five. Similar folds, as already stated, occur in the 
caecum, but do not extend as far as its blind end. The caecum 
is proportionately and actually larger than in any other Marsupial. 
The gall-bladder is unusually elongated. 
The Koala is mainly crepuscular or nocturnal in its habits. It 
feeds so exclusively upon the leaves of the gum-tree (Hucalyptus) 
Fic. 70.—Koala. Phascolarctos cinereus. x, 
that it is umpossible to keep the creature long in captivity in 
lands where that particular kind of food is not available. 
The female, though she seems to bear but a single young one, 
which is carried on the back after the fashion of some Opossums, 
has two nipples. The animal’s slow habits seem to require a 
nocturnal and retired life. It is about as lethargic as the 
Sloth, and it is said to further resemble that animal in clinging 
firmly to a branch even after it is shot. 
