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INTRODUCTION. Vv 
the form of thin plates or scales; these are much thickened in the Hawk- 
bill, Eretmochelys, and form the tortoise shell of commerce; they are hardly 
noticed in such genera as Trionyx and Sphargis. The feet and limbs vary 
ereatly according to habits. Marine species have broad paddles in which 
the toes are not distinct, and the claws appear as hooks on the margin. 
Certain fresh-water species have the toes broadly webbed and furnished 
with strong claws for tearing to pieces the creatures on which they feed. 
And in the land Turtles, Testudo, foot, ankle and leg resemble clubs or 
the feet of elephants. The skull is short, massive, and bears but a single 
condyle. Ordinarily the neck is long and flexible, and the tail is short; in 
sea turtles, however, the neck is comparatively short, and the tail of the 
“Snapper” is long. 
The sight is keen. The eyes are usually somewhat large and very 
mobile; they are protected by two lids and a nictitating membrane. The 
hearing is tolerably acute; the tympanum is not protected by valves or 
cavity. As would be expected from the mode and infrequency of breathing, 
the sense of smell is dull. The tongue is thick and fleshy. From the man- 
ner in which domesticated species select their food, there can be little doubt 
of the possession of taste. This sense is probably more developed in the 
vegetable-eating land tortoises. No specialized tactile organs are known, 
unless, it may be, in the fleshy lips of some or barbels in exceptional cases, 
as the Matamata. Respiration is effected by muscular exertion or swallow- 
ing. Many, if not all, turtles have voice. The most recent verification of 
this has been in Calemys Muhlenbergii, by Dr. Abbott. Few creatures are 
more sensitive to changes of the weather. A passing cloud often drives 
them to shelter. 
All turtles are oviparous. The eggs are fertilized within the oviduct; 
they are deposited in the sand or earth, and left to be hatched by the heat 
of the sun. The ovaries and testes are paired; the intromittent organ of 
the male is simple. When in copulation the male is carried on the back 
of the female. On the paddle of male sea turtles the first claw is modified 
so as to form a hook to grasp the edges of the shells of their mates. Males 
of many species are distinguished by a depression or concavity in the 
plastron. 
Land Turtles generally have a well-ossified, high-arched shell, club feet, 
and long necks. They travel slowly, feed on vegetables, and are able to 
endure fasts of great length. Sometimes they make long journeys for 
