X 



$62 FRESH-WATER BIOLOGY 



/ have filled it. The contractions take 



/ place frequently, so that a large amount 



of fluid is expelled. 



Besides its organs for the nutritive 

 CI processes, the rotifer has of course or- 



gans for causing and controlling move- 

 ments. The chief organ of locomotion 

 is the ciliated corona. By its aid the 

 rotifer may either creep along, over 

 ^\ surfaces, or swim freely through the 



water. When swimming freely the ro- 

 tifer usually revolves on its long axis, 

 so as to follow a spiral course (Fig. 862). 

 Changes of form and movements of 

 parts of the body are brought about 

 by many slender muscles (Fig. 857, C, 

 ms). These muscles are either appKed 

 closely to the body wall or pass from 

 the body wall through the body cavity 

 to other parts. The muscles are often 

 striated. 



An important organ for producing or 

 guiding motion is found in the foot 

 with its toes. The foot of the notom- 

 matid is usually short; it is nothing 

 more than that part of the body be- 

 ^ hind the cloaca. It usually tapers 



somewhat, but is not clearly marked 

 off from the rest of the body, as it is 

 in some rotifers of other families. At 

 its posterior end it bears side by side 

 a the tapering, pointed toes, which are 



usually small in the Notommatidae. 

 The toes serve as a steering apparatus 

 in swimming, and as points of sup- 

 port and attachment in creeping. For 

 attachment the toes are supplied with 



Spiral path followed by swim- 

 ifer, as seen in Di 

 (After Jennings.) 



F1G.862. 

 ming rotifer, as seen in Diuret'ia tisris 

 MiUler. 



