CROCODILES 245 



colour with dark spots, scarcely distinguishable from the rocky soil on 

 which it lives. Its length is about 5 feet, and at the extremity of its 

 body it is provided with a peculiar structure, "the rattle" (hence its 

 name), which consists of a series of hollow horny rings; these are 

 portions of the epidermis left after the successive castings of the skin. 

 When the animal shakes its tail, these horny rings, rubbing against 

 each other, produce a rattling noise. The snake, however, never shakes 

 its rattle while creeping slowly along or when in quest of prey (consisting 

 of small vertebrates), but only when if believes itself in danger, which 

 shows that the rattle is really a means of inspiring fear in its enemies. 



ORDER III.: CROCODILES (CROCODILIA). 



Body of lacertilian shape, with long, laterally-compressed tail ; bony 

 dermal scutes developed on the back ; four legs ; teeth lodged in sockets. 



The Common Crocodile (Crocodilus niloticus). 



(Length up to 20 feet.) 



The crocodile has the shape of a gigantic lizard, and, like all the 

 members of this order, is an inhabitant of the water. It is found in 

 the rivers and lakes, both large and small, of nearly the whole of Africa 

 and some of the neighbouring islands. In the lower course of the Nile, 

 however (from which river it derives its specific name), it has almost 

 disappeared, as a result of the traffic of rapid steamers of deep draught 

 and of incessant persecution, for the bullets of modern firearms are 

 able to penetrate its powerful armour, which consists of horny scutes, 

 supported, especially on the back, by large bony plates developed in the 

 subjacent dermal layer. The scutes of the back are carinated (see 

 viper) ; those of the tail carry in its fore-part double, towards the end 

 single, toothed ridges. The colour of the monster is a dark bronze green. 

 During the daytime it lies asleep in the sun on a sand-bank or muddy 

 shore, having all the appearance of some weathered old tree-trunk. At 

 nightfall it rouses itself for the pursuit of its prey. The vertical, very 

 dilatable pupil indicates its nocturnal habits. (Compare with cat.) Its 

 laterally-compressed, powerful, and very movable tail, which acts as a 

 propeller (see tadpole of frog and newt), and the webbed toes of the hind 

 feet render it an adept and rapid swimmer. It cleaves the waters as 

 easily as an arrow does the air. The auditory passages can be closed 

 by two folds of skin, and the nostrils by the pressing together of their 

 swollen edges, arrangements which enable the animal to remain below 

 the water for a prolonged period. (Compare in this respect aquatic 



