CHAPTER VII 

 PHYLUM PLATYHELMINTHES 



The Phylum Platyhelminthes (Gr. platus, broad; helmins, 

 an intestinal worm) includes the planarians, liver-flukes, tape- 

 worms, and many other " flatworms." Some of these are free 

 living in fresh water, salt water, or less frequently on land, 

 whereas others are parasitic. Many of the parasites pass through 

 a number of complex stages, and live in the bodies of several 

 species of animals during their life-history. The parasitic flat- 

 worms frequently are responsible for serious diseases of man 

 and other animals. 



The three classes of the Platyhelminthes are as follows: — 



Class I. Ttjrbellaria (Lat. turbo, I disturb), with ciliated 

 ectoderm; free-living habit {Planaria, Fig. 97); 



Class II. Trematoda (Gr. trema, a pore; eidos, resemblance), 

 with non-ciliated ectoderm; suckers; parasitic habit (Fasciola, 

 Fig. 105); and 



Class III. Cestoda (Gr. kestos, a girdle; eidos, resemblance), 

 with body of segments; .without mouth or alimentary canal; 

 parasitic {Tcenia, Fig. 107). 



1. A Fresh- water Flatworm — Planaria 



Planaria (Fig. 97, and Fig. 98, 2) is a flatworm found only 

 in fresh water, usually clinging to the underside of logs or stones. 

 Its body is bilaterally symmetrical and dor so-ventr ally flattened. 

 The anterior end is rather blunt, the posterior end, more pointed. 

 It may reach half an inch in length. Planaria maculata, the 

 common American species, is difficult to study because of the 



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