THE CROCODILE. 93 



contraction of the body enabling it to render itself for 

 a time heavier than an equal bulk of water. 



We will now revert to our water trespassers, and 

 take one of the most perfect of the lizard trespassers, 

 namely, the Crocodile, with which the Alligator will be 

 included. There is really but little difference between 

 these two groups of large aquatic lizards, and it is not 

 necessary to describe the marks by which they are 

 distinguished. The word " crocodile " will, therefore, 

 be understood to signify the various species of Crocodiles 

 and Alligators, the structures which enable them to 

 trespass upon the water being practically the same in 

 all the members of both groups. 



Beginning with the first necessity of life i.e., 

 respiration we shall find in these huge lizards a most 

 wonderful provision, which enables the animal to respire 

 under disadvantageous conditions. 



In the first place, the peculiar cellular structure of 

 the lungs in all lizards assures a slow aeration of the 

 blood, so as to suit the sluggish and cold-blooded cir- 

 culation of these creatures. 



A very little amount of respiration is therefore 

 needed in these creatures, which are able to pass a 

 considerable time without any respiration at all. This 

 may be easily tested by watching the specimens at 

 the Zoological Gardens, which lie flat on the bottom 

 of their tanks for a very long period, looking as life- 

 less as if "they were sham Crocodiles made of cast iron, 

 and apparently regardless of the fact that they are 

 completely covered with water. 



Something more is, however, needed. The Croco- 



