I 68 COLLEGE ZOOLOGY 



once from the Indian Ocean and once from New Britain. Ccelo- 

 plana inhabits the Red Sea. 



Economic Importance of Flatworms. — The Turbellaria are 

 of practically no economic importance. Trematodes are para- 

 sitic in a great many vertebrates, but for the most part do not 

 cause serious injuries. The liver-fluke of the sheep, and the 

 trematode Schistosoma haematobium which infests the blood- 

 vessels of the urinary bladder and alimentary tract of man, in 

 Africa, are the most important species. 



The adult tapeworms found in the alimentary canal of man 

 and other animals interfere seriously with the digestion and 

 absorption of food, but the larvae are more dangerous. For 

 example, the tapeworm, Taenia echinococcus , which lives as an 

 adult in the dog, gives rise to a larva called Echinococcus poly- 

 morphic. These larvae may form large vesicles in man, known 

 to physicians as hydatides, which may break with serious or even 

 fatal results. The organism which causes " gid " or " staggers " 

 in sheep is the larva, called Ccenurus cerebralis, of the dog tape- 

 worm, Taenia ccenurus. It becomes lodged in the brain or 

 spinal cord. Goats, cattle, and deer are also attacked by the 

 same species. 





