A ROTIFER (Wheel Animalcule). 



Phylum VI, TROCHELMINTHES; class i, ROTTFERA; order 2, BDELL- 



OIDA, or order 3, PLOIMA. 



HABITAT. Rotifers are found in large or small bodies of water, both 

 salt and fresh, in almost any quarter of the globe. They are common 

 in ponds and stagnant pools and about the accumulated sediment 

 and other inert material in aquaria. 



Technical Note. On account of their minute size rotifers must be 

 studied -with the aid of the compound microscope, the lower powers 

 being usually sufficient for the purpose. Mount bits of "vegetation 

 and scum from aquaria or stagnant pools and look for small organ- 

 isms having a sort of forked tail and a broad anterior region. The 

 latter ends in a disc furnished with what is apparently a rapidly 

 rotating circlet of cilia. If possible, select for study specimens that 

 are attached by the tip of the tail, rather than those that are swimming 

 about. 



APPEARANCE. The wheel animalcules are minute, active creatures 

 almost microscopic in size. They are somewhat larger than the Proto- 

 zoa, however, partially transparent, and when swimming about do not 

 exhibit the jerky movements of the cyclops. They are probably often 

 mistaken for Protozoa, but the resemblance is only superficial. In 

 spite of their minute size, they are many-celled animals having well 

 developed systems of internal organs. 



MOVEMENTS. Watch the animal's movements from place to place. 

 Does it creep with a sort of looping motion or swim freely ? Species 

 of the order Ploima move in the latter manner only; rotifers of the order 

 Bdelloida adopt both methods of locomotion. Can you make out the 

 organs of locomotion used in swimming? Which end is directed 

 forward in progression ? Is this always the case ? Determine whether 

 there is a distinction of dorsal and ventral surfaces. Can any portion 

 of the body be shortened up telescoped or retracted ? 



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