FRESH-WATER ANIMALS. 309 



whicli the body is enclosed. They are remarkably flat and 

 expanded at the sides, so that they can lie in wait unob- 

 served in the mud at the bottom of rivers and lakes, watch- 

 ing for the passing by of any little living dainties to whicli 

 they may take a fancy; when, suddenly, the long neck is 

 darted forth, and the captive, be it iish, mollusc, frog, lizard, 

 or insect, is seized, drawn down, and devoured, without its 

 captor taking the trouble to move from his hiding-place. 



Marine Tortoises, or Turtles, constituting the family of 

 Cheloniadce, are still more perfectly formed for swimming. 

 The body is fiat ; the shell too small to admit the retraction 

 of the head and feet ; and the feet are formed into paddles 

 as perfect as those of tlie Seal. Their food, like that of the 

 Land Tortoise, is almost entirely vegetable. 



There are many good specimens, Eni^s concentrica, etc. 

 (Plate XX.), in the fish-house of the Gardens, in company 

 with some juvenile Crocodiles and some other species of 

 Em2/s. The Crocodiles seem to keep apart from and to 

 take no notice of their companions ; but the Tortoises 

 crawl very freely over each other^s backs. In general their 

 movements are slow enough, but at times, when pursuing 

 their food, they are capable of some degree of animation. 

 Sometimes the Emycles will creep gradually and cautiously 



