198 ZOOLOGY. 



dividuals are produced in one host, and the eggs or larvae pro- 

 duced by them find their way into another species of host where 

 a portion of the development toward maturity occurs. The 

 transfer of the parasite from the second back to the first host- 

 species is necessary to complete the cycle. In some instances 

 there is not a change from one animal to another, but merely 

 from one organ to another in the same animal, as in Tcenia 

 murina of the rat. In size the unsegmented worms vary 

 from minute microscopic dimensions to thirty feet in length 

 in the tape-worm, Bothriocephalus latus. Some suggestion of 

 their importance to man and the higher animals may be 

 gathered by reference to the following table (p. 199). 



232. Supplementary Studies for the Library. 



1. In what different ways are the forms included in this 

 chapter classified in the various text-books to which you have 

 access ? 



2. Consider the economic importance of the parasites in- 

 cluded in this chapter. 



3. Make a further study of the life histories of selected 

 representatives of these parasites. 



4. Illustrate by means of the unsegmented worms the de- 

 generation and simplification which attends parasitism. 



5. In what various ways do the intestinal parasites in the 

 group adhere to the walls of the digestive tract of the host? 



6. Do you think the domestic animals are more or less 

 likely to be attacked and suffer from these internal parasites 

 than the wild? What evidences would you offer for your 

 view? 



7. Prepare for the class a diagram of the reproductive 

 organs in the Tape-worm, indicating the function of each of 

 the portions. 



8. What is meant by the " dermo-muscular " sac in worms? 

 Its functions? 



9. Report on the importance of the Brachiopods in early 

 geological time, with the main structural features of the class. 



