HpARINOF WWE PILES 
lizards and snakes. The size is greater than that of 
any lizard; but it must be remembered that a large 
monitor lizard comes not far behind a smallish croco- 
dile. Crocodiles are invariably aquatic, lizards are 
very rarelyso. We must necessarily mention a few in- 
ternal characters to emphasize the separation of lizards 
and crocodiles. In the latter the teeth are always 
confined to the upper and lower jaws; in lizards they 
stray on to the bones of the palate in many cases ; 
furthermore each tooth of a crocodile is implanted in 
its own particular socket, while in lizards the teeth 
are attached side by side to the bones which bear them 
without lying at some distance apart and each like 
a peg inaholein these bones. The heart of the croco- 
dile is more completely four-chambered than is that 
of the lizard, in some of which, however, there is a 
tendency in the same direction. On the whole the 
lizard tribe is on a lower level of organization. Lizards 
are excessively numerous and occur in almost all parts 
of the world, except in very cold regions, such as the 
extreme north. They chiefly abound in the tropics. 
The general aspect of a lizard is familiar to every one. 
But it is not so easy as it seems to differentiate a lizard 
from a snake. For among the lacertilia there is a 
distinct tendency to lose the limbs, an event which 
has occurred in many of the families into which the 
order is divisible, and thus produces a likeness to a 
snake which is after all superficial. Nevertheless, the 
two orders, the Lacertilia and the Ophidia, are very 
nearly akin. Some differences between them will be 
dealt with later. 
THe HELODERM LIZARD 
Of lurid coloration is the Arizona heloderm, or “ gila 
monster’ as it is often termed in the United States, 
in the southernmost of which it lives. There would 
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