VIII. FLATWORMS, ROUNDWORMS, AND 

 ROTIFERS 



Branches IV, V, VI, and VII. — Platyhelminthes (Flat- 

 worms), Nemathelminthes (Roundworms), Trochelmin- 

 thes (Rotifers), and MoUuscoidea (Lamp Shells) 



In this chapter we shall discuss examples of four branches 

 the members of which, heretofore, have all been included in 

 one branch. Vermes (worms) . The individuals, commonly 

 placed in the branch Vermes, differ so much among them- 

 selves that the later authorities put them in different 

 branches. The members of the above branches are more 

 or less wormlike in character and appearance. The body 

 of the earthworm, as we know, is divided into rings, or 

 segments; but no true segments are foimd in the simpler 

 worms. The animals treated in this chapter are perhaps the 

 most widely distributed of all the many-ceUed animals. 

 Some are found from the shallowest to the deepest water 

 in rivers, lakes, a,nd seas; some live on the land; while 

 some live as parasites in many different species of the 

 multicellular animals. 



Flatworms 



The flatworms include a great variety of forms that 

 differ widely from each other in habits and appearance. 

 The majority have flattened, more or less leaflike bodies; 

 a few have approximately cylindrical bodies. The fresh- 

 water flatworms, found on the bottoms of ponds among the 

 sediment and leaves, are from one eighth of an inch to 

 nearly half an inch in length. Their bodies are flat, thin, 



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