456 CHELONIANS. 



State what is peculiar in the heart of Reptiles. Explain the circulation of 

 the blood in Tortoises, Lizards, &c. What striking facts are given respect- 

 ing the blood of Reptiles? What is at first the condition of the Amphibia? 

 What change do they undergo ? Is this true of all of them ? How do some 

 of them differ ? Explain the circulation in both divisions. How many limbs 

 have Reptiles ? Does their internal structure differ from that of Quadru- 

 peds ? What is said of their covering ? What of their organs of sense ? 

 How are they usually produced ? How do they dispose of their eggs ? How 

 is it with the VIPER ? What is said of the diffusion of Reptiles V Upon 

 what do they feed ? How many species do they include ? Name the OR- 

 DERS into which they are divided. Point out on the Chart some animals be- 

 longing to each of these orders. 



SECTION II. 

 FIRST ORDER. CHELONIANS, or TORTOISES. 



CHELONIA. (Gr. xMvi], chelone, a tortoise.) 



The Tortoises may be arranged into the following divisions, 

 viz: (1) LAND TORTOISES; (2) MARSH and RIVER TORTOISES; 

 (3^ MARINE TORTOISES or TURTLES. 



They differ most widely from the general form of the class; 

 for (1) They are clothed with a natural armor, not like that of 

 the Armadillo, a simple, hofny addition to the skin, but a part of 

 the skeleton itself. The skeleton is, in fact, thrown to the out- 

 side of the body, so as to form an external bony envelope, covered 

 with a horny or leathery sheathing, and enclosing, as in a box, 

 the internal organs, and other parts of the bony frame-work 

 which do not immediately enter into its composition. Tortoises 

 may be likened to Frogs, so enveloped in horny armor as to be 

 restrained by it from jumping. 



The upper piece, or dorsal buckler, is termed the carapace. 

 This is usually more or less arched, and consists of an expansion 

 of the ribs into wide flat bones, all united firmly together, and 

 also to the edge of the flattened spinal processes, the whole 

 forming a consolidated plate. (Plate XII. fig. 1.) To the 

 margin of the plate thus formed, is added a third set of bones, 

 regarded as representing the sternal ribs of the Crocodiles and 

 other Lizards, and assisting to complete the circumference of 

 the carapace. 



The lower plate, or abdominal buckler, is termed the plastron 

 or sternon. This, instead of being prolonged forwards into a 

 keel to afford attachment to large muscles, as in the Birds, is ex- 

 tended sidewise for the protection of the body. It consists of 



