94 LABORATORY MANUAL FOR ELEMENTARY ZOOLOGY 



of the lungs of the frog; the bladder fluke, Gorgoderina, inside the urinary bladder ; 

 and Clinostomum, occurring in cysts in the peritoneum. Eggs and embryos of 

 flukes frequently occur in the frog also. 



3. Tapeworms or cestodes. The tapeworms are degenerate flatworms living 

 as internal parasites, commonly in the digestive tracts of vertebrates. They 

 are extremely long, tapelike animals, as the name implies, with a small head, 

 provided with hooks or suckers or both for clinging, and a body made up of a 

 great number of joints, or proglottids. Each proglottid contains a complete 

 set of the complicated reproductive organs, and when ripe they drop off from 

 the posterior end of the worm so as to infect new animals. 



