INTRODUCTION. IX 



and have a hard shell; they are left in holes in the earth and sand to 

 hatch. The cloacal aperture is a longitudinal slit; the penis is single. 

 The Rhizodonts are long lived; the young grow rapidly, adults more 

 slowly. Specimens have been taken of lengths greater than fifteen feet. 

 When swimming they propel themselves by the tail, the webs between 

 the toes in many species being of more service in lifting them from the 

 mud. 



Voice in this group seems to be limited to a sort of suppressed bellow 

 or blowing noise. Habits vary in different genera; some are nocturnal, 

 others diurnal. In regions affected by protracted drouths some bury them- 

 selves in the mud before it hardens, and reappear when the rains have 

 again softened it sufficiently to allow them to release themselves. Some 

 are very dangerous. Natives in crocodile-infested regions are able to free 

 themselves when seized by the creatures by thrusting the fingers into the 

 eyes. Few animals are harder to kill. A hook baited with flesh and tied 

 to a number of small cords, which get between the teeth, is the best means 

 of capture. Caught in this way the powerful blows of the tail are effec- 

 tively used in defense. 



The common North American representative of the order is the Alli- 

 gator, ranging from Florida to Tehuantepec. Stragglers have been 

 reported as far north as the mouth of the Ohio river. A crocodile, C. 

 mnericanus, ventures north along the coasts of Mexico from Central 

 America. Another, probably C. intermedins, from the West Indies, is 

 occasionally found in Florida. 



Sauria. 

 The transition from this order to the preceding and to the following is 

 so gradual that it is next to impossible to cite characters that shall be gen- 

 eral and exclusive. In a general way animals belonging to this order are 

 distinguished from the Rhizodonts by dentition, squamation, structure of 

 heart, structure of ear, transverse anal aperture, and male sexual organs, 

 and from the Ophidians by lack of motion of maxillae and other bones 

 of the head, elastic symphysis of mandibles, structure of ear, structure 

 of eye, and presence of limbs. It will be seen at once that there are 

 numerous exceptions, especially in regard to the separation from the ser- 

 pents. Scolecophidia have the bones of the head more firmly united than 

 other snakes, and some agree with the Amphisbasmc of the Sauria in the 



