CHAPTER XVII 

 THE WHEEL ANIMALCULES (ROTATORIA) 



By H. S. JENNINGS 



Professor of Zoology, Johns Hopkins University 



The Rotatoria or Rotifera are perhaps the most characteristic 

 group of fresh-water animals, and at the same time the most 

 attractive and beautiful. They are everywhere abundant in fresh 

 water, but are rare elsewhere. With their varied and fantastic 

 forms, their brilliant colors and lively manners, they have long 

 been the favorites of amateur microscopists. Some of the older 

 observers have expressed themselves with great enthusiasm in 

 regard to these creatures. Eichhorn (1781) who discovered Steph- 

 anoceros in 1761, calls it the "crown polype," and likens this "in- 

 comparable animal" to a pomegranate blossom. Of Floscularia he 

 says, "Now I come to a very wonderful animal, which has very 

 often rejoiced me in my observations: I call it the Catcher: ex- 

 traordinarily artistic in its structure, wonderful in its actions, rapid 

 in capturing its prey." Eichhorn's account of the capture of prey is 

 excellent: "Its head was a widespread net . . . with points which 

 had little round balls on their tips; so it awaits its prey; when a 

 little animal came into this net or hollow basin, then it convul- 

 sively drew the neck a little together, as if to find out, as it were, 

 whether it had really gotten its booty; then it suddenly folded the 

 net together and pushed the prey into its body, where one could 

 still see it plainly. . . . And I have often seen it exactly as in 

 [Fig.] K; then it looked terrible, no lightning stroke can rush from 

 the clouds into the air so quickly as this little animal fiercely struck 

 together the two hooks when it noticed a prey in its outspread 

 net." 



The rotifers are minute, chiefly microscopic animals. Their 

 most characteristic feature is the ciliated area at or near the ante- 

 rior end of the body, serving as a locomotor organ or to bring food 

 to the mouth. Taken in connection with the lack of cilia on other 

 parts of the body (save in rare cases at the posterior end), this 



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