the sun’s heat or the heat resulting from the fermentation of decaying plant 
matter. 
In the amphibians a three-chambered heart propels the blood, but in 
reptiles there has emerged a four-chambered organ. This type is carried 
forward by the birds and mammals, which are still higher forms of evo¬ 
lutionary development. 
The theory that the more individual variations a group possesses, the 
greater is its chance for survival, is exemplified by the reptiles. And each 
species, with its different environment, has developed along individual lines. 
For instance, there is a considerable range of locomotor adaptations. Snakes, 
lacking functional limbs, travel by lateral, undulating waves of the body 
muscles; most lizards and all turtles are four-limbed; crocodiles swim 
chiefly by strokes of the flattened tail; and the “flying dragon” lizard of the 
Indo-Malayan region, while it does not actually “fly,” soars glider-like from 
tree to tree by means of its distensible winglike skin membranes. 
Thus, while reptiles have retained such common features as the dry, 
scaly skin, their dissimilarities are even more striking. Tree snakes tend 
to have long slender bodies which enable them to “swim” over the leaves 
and branches. Often cave dwelling reptiles are without skin pigment and 
sight. Desert dwellers generally have the pallid coloration of their sur¬ 
roundings. 
Suited to their environment, many reptiles, like other animals, have 
a protective coloring which blends with the background and makes them 
virtually invisible. Some reptiles are able to assume various colorings; for 
example, when some lizards want to attract mates during the breeding sea¬ 
son, their skins assume the bright and glaring colors of the dandy, thereby 
probably aiding members of the same species to locate each other. 
Other means of protection include bony shells, poison and musk dis¬ 
pensing glands, and organs of smell to catch the scent of an approaching 
enemy. The flattening of the cobra’s hood, the rattle of the rattlesnake, and 
the hisses of other species might be considered as means of protection for 
they possibly notify the enemy to stay away — or suffer the consequences. 
It is also possible that these reactions are mere manifestations of fear. 
Such illustrations, chosen at random, reveal the intrinsic appeal of 
one of the most important divisions of the earth’s inhabitants, neighbors 
of man with which man should become acquainted. 
19 
