CROCODILES. 69 



celerity on the slightest alarm. A fully adult 

 example measures about eighteen feet. 



The slenclerness of the jaws seem, as in the 

 Gharial, to be correlated with the feeding habits. 

 Neither the one nor the other appears, except 

 rarely, to attack large prey. This seems to 

 support the view that the short-snouted forms 

 have acquired this characteristic by adaptation to 

 the requirements for the capture of powerful 

 prey, such as the large mammalia. 



With the Caimans and Alligators we may close 

 this chapter. Closely allied, they are to be 

 distinguished from the Crocodiles by the fact 

 that the fourth lower tooth is received into a 

 socket in the upper jaw instead of a notch. 



Alligators appear to have been common in 

 Europe in past ages, for their remains occur in 

 the pluviatile deposits of the Upper Chalk, and 

 they survived until the Pliocene age. Possibly 

 their extinction was due to climatic changes, 

 for at this time the tropical types of vegetation 

 seem to have begun their retreat southwards in 

 the European regions, and this may have been 

 followed by a similar retreat on the part of the 

 animals dependent thereon. At the present day 

 but two species of Alligators are known. One of 

 these, strangely enough, occurs in the rivers of 

 China, the other in the Southern States of North 

 America. 



The American species (Alligator mississippiensis) 

 seems to have fallen on evil days. They are being 

 slain by the thousand for the sake of their hide ; 

 and settlers wage unrelenting war on them for the 

 ravages they make upon their pigs. As a con- 



