sensitivities ranging from the near ultraviolet to red. (For a description of rods and cones,
see chapter titledControlling the Body). Turtles have a rigid beak and use their jaws to cut
and chew food. Instead of teeth, the upper and lower jaws of the turtle are covered by horny
ridges. Carnivorous turtles usually have knife-sharp ridges for slicing through their prey.
Herbivorous turtles have serrated-edged ridges that help them cut through tough plants.
Althoughmanyturtlesspendlargeamountsoftheirlivesunderwater, allturtlesandtortoises
breathe air, and must surface at regular intervals to refill their lungs. They can also spend
much of their lives on dry land. Turtles lay eggs, like other reptiles, and which are slightly
soft and leathery. The eggs of the largest species are spherical, while the eggs of the rest are
elongated. In some species, temperature determines whether an egg develops into a male or
female. Large numbers of eggs are deposited in holes dug into mud or sand. They are then
covered and left to incubate by themselves. When the turtles hatch, they squirm their way
to the surface and head toward the water.
Importance of Reptiles
The chief impact of reptiles, such as lizards, on humans is positive as they are significant
predators of pest species. Snakes are also very useful rat exterminators, for example, in the
Irula villages of India.
Reptiles can be important as food sources: green iguanas are eaten in Central America, the
tribals of “Irulas” from Andhra Pradesh and Tamil Nadu in India are known to eat some
of the snakes they catch, Cantonese snake soup is consumed by local people in the fall to
prevent colds, cooked rattlesnake meat is commonly consumed in parts of the Midwestern
United States, and turtle soup is widely consumed.
Reptiles also make good pets. Numerous lizard species are prominent in the pet trade. In
the Western world, some snakes, especially docile species such as the ball python and corn
snake, are kept as pets. Turtles, particularly small terrestrial and freshwater turtles, are
also commonly kept as pets. Among the most popular are the Russian tortoises, Greek
spur-thighed tortoises and red-ear sliders (or terrapin).
For medical and scientific research, snake venom collected by the “Irulas” is used for pro-
ducing life-saving antivenin and for other medicinal products. Observations about turtle
longevity (the liver, lungs and kidneys of a centenarian turtle are virtually indistinguishable
from those of its immature counterpart) have inspired genetic researchers to begin examining
the turtle genome for longevity genes.
Finally, reptiles play a significant role in folklore, religion and popular culture. Lizard sym-
bology plays important, though rarely predominant roles in some cultures (e.g. Tarrotarro
in Australian mythology). The Moche people of ancient Peru worshipped animals and of-
ten depicted lizards in their art. Crocodilians have starred in several science fiction movies
such as Lake Placid and DinoCroc. There are also many cultural depictions of turtles and