144. THE AUSTRALIAN NATURALIST. 
in the particular species, and is'a very striking case of conver- 
gent retrogressive evolution. 
The Pygopide is a family of legless lizards confined to 
Australia and neighbouring islands. There are altogether about 
ten species, most of which are peculiarly snake-like in appear- 
ance. The Victorian species of Delma is supposed to mimic 
the young of the brown snake, Diemenia textilis, and it is indeed 
extraordinarily like it. Some of the species, as Lialis burtoni 
and Pygopus lepidopus are distributed over the whole of 
Australia. 
The CHAMELEONS, with their casque-like skulls, peculiar 
circular eyelids and protruding eyes, with which they squint 
horribly, theix prehensile tails, and hands and feet in which 
the digits are bound up into two bundles, three digits in one 
bundle and two in the other, thus converting the hands and 
feet into very efficient grasping organs, are rather widely 
separated in structure and appearance from the rest of the 
lizards. They possess very long and mobile tongues, which are 
capable of being darted out to a distance of six or seven 
imches to lick up insects and the like. They shoot their 
tongues with very great precision, hardly ever missing their 
object. The remarkable changes of colour of which their skin is 
capable are well known to everyone; they are easily kept in 
captivity, and make very charming pets. 
GeocrapnicaL Disrripution. The study of the geographical 
distribution of animals teaches us broadly two main lessons: 
(1) It throws much light on the past geographical 
history of the earth, and (2) it is a great aid in understanding 
the relationships of various groups of animals. It is a very 
important factor in the elucidation of the problem of the 
evolution of animal life. 
A natural family of animals is one in which all the members, 
the various species, are all descendants of common ancestors: 
represent, in fact, a branch of the family tree. 
The present classification of animals, especially apart from 
the larger groups, is far from final, and is constantly under- 
going revision as new facts are added, or previously known 
but misunderstood facts come to be better understood. And 
when we find a family of animals widely distributed, and more 
especially if this distribution is discontinuous, we should very 
closely scrutinise the various facts on which the relationship is 
based to make sure whether it is a natural family or not. 
The Geckos, though a very large and widely-distributed 
family, are a natural family ; one of the most independent and 
compact families of lizards. That is, while a study of their 
structure shows all their members to have a close structural 
similarity, they are not very closely related to other families 
of lizards. ‘They are found to occur in practically all the 
