142 THE AUSTRALIAN NATURALIST. 
The order Lacertilia is divided into three sub-orders :—(1) 
the Geckones, comprising the single ‘family Geekonidae; (2) 
the Lacertae, which includes eighteen families; and (3) the 
Chamaelontes, embracing the single family of the Chamaeleons. 
As already mentioned the Geckos are a large and widely- 
distributed family, containing 50 genera and about 270 species. 
There is a great uniformity of structure throughout the family, 
‘and the generic differences are of rather an unimportant nature, 
and refer for the most part to the structure of the digits. The 
skin is nearly always soft, and bears little granules or tubercles 
on the dorsal surface. ‘he body is more or less depressed, and 
in some cases is bordered by cutaneous expansions, which en- 
able the animal to adhere better to the vertical surfaces over 
whichit runs. The lamellae on the digits are so arranged as’ 
to produce numerous little vacua, which are so effective that 
the gecko can not only climb smooth, vertical surfaces like the 
walls of a room, but can run across the ceiling, back down- 
wards. The shape of the tail in geckos is subject to a great 
amount of variation, assuming some curious and grotesque 
forms, andin many cases being curiously large in comparison to 
the size of the body. 
Many of the geckos are arboreal, living on shrubs or trees. 
Nocturnal in their habits, they generally conceal themselves 
under bark or stones in the daytime; but they are fond also. of 
basking in thesun. Many have become the commensals’ of 
man, especially in India; some live inside the house, others 
outside. Of those living inside, one species may live in the 
walls, another in the roof, while a third may inhabit the dark 
cellars. They are very regular in their habits, always return- 
ing to their own special spot when disturbed or when finished 
foraging. At the same time of day, too, an individual may be 
seen in the same spot day after day, perhaps for months. 
Living on flies and spiders they perform good service for the 
houses in which they live. One species, rather large in size for 
a gecko, lives on young rats. ‘hey are absolutely harmless to 
man, their teeth being so small that they could hardly break 
the skin by a bite; yet, strange to say, some of them are much 
feared, not only in Australia, but in almost every country in 
which they live. 
The eighteen families of the Lacertae are characterised by 
the presence or absence of osteoderms, z.e., bony plates in the 
integument, the character of the teeth and tongue, and the 
structure of the skull. 
The Agamidae is a family of old-world lizards most nume- 
rously represented in Australia. . The great frilled lizard of 
Northern Australia, Ohlamydosaurus king, is one of the most 
striking and best-known members. There is.a large cutaneous 
frill round the neck, into which bony processes from the hyoid 
bone project like the ribs of an umbrella; indeed, the erection 
