CHAPTER XII 



THE FREE-LIVING FLATWORMS 



(TURBELLARIA) 



By CAROLINE E. STRINGER 



Head of the Department of Biology, Omaha Eigh School 



The Turbellaria or free-living flatworms are among the most 

 interesting of the simply organized animals because of the re- 

 markable variety shown in their reactions and behavior. They 

 are to be found both in fresh and salt water and sometimes in 

 moist places on land. The fresh-water forms are common in 

 ponds and streams almost everj^where. Many of the smaller 

 forms resemble infusoria in their minute size, shape, and move- 

 ments. The larger Turbellaria are more readily recognized as 

 worms but are often confused with leeches which they resemble 

 superficially in color and form, aitnough they are easily distin- 

 guished by their head-like anterior end, non-segmented body, and 

 lack of posterior adhesive sucker. 



Probably the first attempt to describe one of this group dates 

 back to 1744 when Trembley included in his memoir on Hydra 

 what was undoubtedly a planarian. As early as 1776 0. F. 

 MuUer separated the Turbellaria and Nemertinea from the para- 

 sitic Trematoda, but it was not until 1831 that Ehrenberg gave 

 to these animals the name Turbellaria because of the tiny cur- 

 rents in the water created by the dehcate cilia which cover the 

 body. Much confusion existed in their classification until the 

 appearance of Lang's work on structure and relationships in 1881 

 and in the next year of L. von Graff's monograph on the Rhab- 

 docoelida. Since then considerable attention has been given to the 

 morphological and physiological as well as to the systematic study 

 of the group. 



Flatworms may be either cylindrical, thread-like, spindle-shaped, 

 or more or less flattened and leaf-like. They range in length 

 from a fraction of a milhmeter to several centimeters. The 



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