BRANCH I/ERMES: THE WORMS 



ganic matter which they capture by means of the currents 

 produced by the vibrating cilia of the " wheel. " Small as 



they are they have a complex 

 body-structure, with well-or- 

 ganized systems of organs. 

 For a long time, however, 

 they were classed by natural- 

 ists with the Protozoa on ac- 

 count of their size. They are 

 found all over the world, 

 mostly in fresh w r ater; a few 

 are marine. More than 700 

 species of them are known. 



An interesting thing about 

 the Rotifers is their remark- 

 able power to withstand dry- 

 ing-up. When the water in 

 a pond or ditch evaporates 

 some of the Rotifers do not 



FIG. 14. A wheel animalcule. ... -11 i T 



Rotifer sp. (From living sped- die, but simply dry up and he 



men, Stanford University.) j n t l ie dust, shrivelled and 



apparently lifeless, yet really in a state of suspended 

 animation. On being put into water they will gradually 

 fill out to their full size and shape, and finally resume all 

 their normal activities. In this dried-up condition Rotifers 

 may persist for a long time, several years even, although 

 otherwise their natural life is short, being probably of not 

 over two weeks' duration. Certain other of the lower 

 animals have this same power of withstanding desiccation. 



