FIELD BOOK OF PONDS AND STREAMS 



Rotifer structures. — Most rotifers are solitary but others are 

 joined together in colonies and while the majority of them 

 move freely through the water, a few are attached to plants 

 or animals. Although they grow in an infinite variety of 

 shapes all of them have circlets of cilia which appear like 

 two rapidly rotating wheels at the front end of the body, hence 

 their name Rotifera or wheelbearers. Small as it is, a rotifer 

 has an outer covering, either a soft or a shell-like lorica (Fig. 

 100, 3), muscles, a food canal, nerves, complicated reproduc- 

 tive systems (Fig. loi). 



Seen under the low power of a compound microscope the 

 wheels of the rotifer prove to be the rims of its corona or 

 head region circled with hundreds of cilia waving so fast that 

 they look like two whirling crowns (Fig. loi). B}^ means of 



HEAD 



CORONA 



BRAIN 

 EYE 



ASTAX 

 GASTRIC GLAND 

 STOMACH 



OVARY 



BLADDER 



FOOT GLANDS 



FOOT 



TOES 



HEAD 



Fig. ioi. — Diagram of a rotifer showing circlets 

 of cilia and mastax. (After F. J. Myers.) 



these lashing cilia rotifers propel themselves through the water 

 and collect their food. A rotifer's mouth is at the lower edge 

 of the corona and its short oesophagus contains the mastax, 

 a food pouch equipped with three teeth which crush and grind 



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