CHAPTER vVIII 

 PHYLUM NEMATHELMINTHES 



THE NEMATHELMINTHES (Gr. nema, thread; helmins, an in- 

 testinal worm) are called round or thread worms. They are 

 usually long and slender, and more or less cylindrical. They 

 may be distinguished from the segmented worms (Phylum AN- 

 NELIDA, Chap. ~XI) by the entire absence of internal and external 

 segmentation. The microscopic animal which lives in vinegar 

 and is known as the vinegar-eel is a nemathelminth. Other 

 roundworms live as parasites in the alimentary canal of man, 

 and other animals, or, like Trichinella (Fig. 113), live for a time 

 embedded in the tissues of the body. 



i. A PARASITIC ROUNDWORM ASCARIS LUMBRICOIDES 



External Features. Ascaris (Fig. in) is a genus of round- 

 worms parasitic in the intestines of pigs, horses, and man. The 

 sexes are separate. The female, being the larger, measures from 

 five to eleven inches in length and about one fourth of an inch 

 in diameter. The body is light brown in color; it has a dorsal 

 and a ventral white narrow stripe running its entire length, and 

 a broader lateral line is present on either side. The anterior end 

 possesses a mouth opening, surrounded by one dorsal and two 

 ventral lips (Fig. 112 a, b, c). Near the posterior end is the anal 

 opening from which, in the male, extend penial seta (Fig. 112 a, 

 a, Sp.) for use during copulation. The male can be distin- 

 guished from the female by the presence of a bend in the pos- 

 terior part of the body (Fig. 112 a, a). 



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