UNSEGMENTED WORMS. 193 



PHYLUM VI. Trochelminthes (or Rotifers). 



209. Practical Exercises (for laboratory and library). Rotifers 

 are almost certain to appear in the water of some of the jars in the 

 laboratory. They are small and require the microscope. Time 

 should not be taken to study them thoroughly, but the following 

 items may be considered: 



What is the general form? Does it change? How does the 

 anterior end differ from the posterior? Are they symmetrical? 

 Find the feature that gives them their name (rotifers, or wheel- 

 bearers) . Where is the mouth ? Follow the course of the digestive 

 tract. Note the object just back of the mouth which is continually 

 at work. What is its nature? Is there an anal opening? 



In what various ways do the animals move ? Are they sensitive ? 

 Do they take food ? What kind ? 



By examining the figures see what range of form is found in the 

 group. What qualities are constant? How do they reproduce? 

 Do you find any signs of segmentation of the body at all? Where 

 are rotifers found in nature? 



PHYLUM VII. Molluscoidea (Polyzoa and Brachiopods). 



210. Library Exercise. Where are these animals found? What 

 are the similarities and what the differences between the Polyzoa 

 and the Brachiopoda? What are the meanings of the names? 

 Show these points by means of parallel columns. 



What is the geological history and importance of the brachiopods ? 

 Where were they formerly classed? Why? Why removed from 

 that classification? 



211. The Place of the Unsegmented Worms in Nature. These 

 animals represent the most varied modes of life. The planarians 

 are terrestrial, fresh- water, and marine; the rotifers are free and 

 occur chiefly in fresh water; the polyzoans are aquatic and colonial 

 animals looking much like the hydrozoa, when we consider the colony 

 as a whole; the brachiopods are marine and may be attached, but 

 are not colonial; the trematodes and cestodes represent all possible 

 degrees of parasitism on all sorts of animals. These animals are 

 found almost over the earth, which suggests that they are old and 

 successful types. There is probably not a single group of the higher 

 forms that escapes being the host of one or more species of these 

 worms. The organs most commonly infested by the parasites are 

 the digestive tract and its glands, as the liver, the blood vessels, 

 the body cavity, and certain tissues in which the blood supply is 



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