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ESSENTIALS OF ZOOLOGY 



Order Strongyloidea. — This is an entirely parasitic group. The 

 males have caudal bursae with rays. The club-shaped esophagus is 

 without a posterior bulb. The hookworms of man, the Strongylus 

 roundworms of horses, and Syngamus trachea which causes gapes in 

 birds by obstructing the windpipe, are all common representatives. 



Order Filaroidea. — This is a completely parasitic order, modified 

 for living in such tissues as lymph, blood, connective tissue, and 



Fig. 122. — Hair "snake," Gordius^ an aquatic roundworm. 



muscle of chordate animals, and transmitted by certain insects. 

 Guinea worm, eye worm, and Filaria are the common human para- 

 sites. Some species cause elephantiasis through occlusion of blood 

 and lymph vessels. This disease results in enormous swelling of the 

 affected parts. These organisms are transmitted by mosquitoes. 

 Several Filaroidea are parasites of horses and dogs. 



Order Dioctophymoidea. — This is another parasitic group living in 

 the kidneys, body cavity, and alimentary canal of mammals and 



