THE NEMATODA. PARASITISM 



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and live in the body cavity till they become adult, when they escape 

 into damp earth, become sexually mature, and pair. After rain the 

 adults sometimes climb the stems of plants in such numbers as to give 

 rise to the legend of " showers of worms." 



Fig. 211.— The Corn-cockle Worm.— From Theobald. 

 A, Cockle gall ; C, larvae ; in D, gall cut open ; E, larvae magnified. 



5. Larva and adults parasitic in different animals, with a free stage. 

 — The Guinea Worm, Dracunculus medinensis. The female, about 

 90 cm. long, encysts beneath the skin of man, usually in the leg, with 

 the head in the host's foot, causing an abscess. She is viviparous. 



Fig. 212. — The Miners' Worm {Ancylostomum duodenale). — From 

 Parker and Haswell, after Leuckart. 



A , Male and female in caitu ; B, anterior end ; C, mouth, with spines ; 



D, hinder end of male, with expansion known as bursa. 



czi.£-. t Cervical glands ; ^k. t pharynx. 



The young escape through the abscess when the host wades in water, 

 and enter the small crustacean Cyclops, with which they are swallowed 

 by a new host. The male is small and has rarely been seen. The 

 diseasejis common in tropical Africa and parts of Asia. The worm is 

 removed by rolling on a twig. If it be broken during this process, 



