Pond Animals 



339 



with oar-like hind legs swung forward, ready, so that a 

 stroke will carry them down below in case of approach 

 of danger. Here hang the wrigglers larvae and pupae 

 of mosquitoes. Here belong the more passive larvae of 

 many beetles and flies and the pupae of swale-flies and 

 certain crane-flies. 



(4). Those that rest down below, equipped with a 

 long respiratory tube for reaching up to the surface for 



FIG. 199. Diagram of distribution of pond life. The right side 

 illustrates the zonal distribution of the higher plants. /, shore 

 zone; 2, standing emergent aquatics; 3, aquatics w i 'th floating 

 leaves; 4, submerged aquatics; 5, floating aquatics; 6, free swim- 

 ming algae of the open water. 



The left side represents the principal features of the distribution of 

 animals, r, s, t, u, forms that breathe air; v, w, x, y, and z, forms 

 that get their oxygen from the water. 



(From the Senior Author's General Biology) 



air. Such are Ranatra, and the rat-tailed maggots of 

 syrphus-flies. 



The animals of the pond that are more strictly aquatic 

 in respiratory habits (being able to take their oxygen 

 supply from the water itself) are so numerous that we 

 shall be able to mention only a few of the larger and 

 more characteristic forms. First there are the inhabi- 

 tants of the bottom. These fall into two principal cate- 

 gories, the free-living and the shelter-building forms. 

 The free-living forms may be grouped as follows: 



