VIII. FLATWORMS, ROUNDWORMS, AND 

 ROTIFERS 



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

 worms), Neniathelniinthes (Roundworms), Trochelmiii- 

 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 ab(_we branches are more 

 or less worndike in character and appearance. The body 

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

 segments; l^ut no true segments are found in the simpler 

 worms. The animals treated in this chapter are perhaps the 

 most widely (Ustributed of all tlie many-celled animals. 

 Some are found from the shallowest to the deepest water 

 in rivers, lakes, and seas; some li^-e on the land; while 

 some live as parasites in many different species of the 

 ludticellular animals. 



Flatworms 



The flatworms include a great variety of forms that 

 differ widely from eacli other iia habits and ap]iearanc<>. 

 The majority have flattened, more or less leaflike bodies; 

 a few have approximate!)' cylin(h-ical bodies. The fresh- 

 water flatwoi-ms, 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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