Flat worms and Threadworms 



299 



Dibothriocephalus latus . 



Drepanidotaenia setigera 



Man and Dog 



Common in Fin- 

 land and regions 

 where fish is a 

 common food. 

 Goose 



In peritoneum and 

 muscles of pike, 

 perch, and trout. 



Water-flea and 

 Cyclops brevicau- 

 datus. 



THE THREADWORMS 



NEMATODA 



The nematodes are the threadworms, or round worms, which make 

 up the phylum Nemathelminthes. 



dtr.efiZAm, 



ZatM 



Fig. 185. A Cross Section, Ascaris Lumbricoides. 



A, Transverse section, cm., cuticle; dl., dorsal line; der.epthm., epidermis; ex.v., 

 excretory tube; int., intestine; lat. L, lateral line; m., muscular layer; ovy., ovary; 

 ut., uterus; v.v., ventral line. 



B. A female cut open to show internal structures. 1, pharynx; 2, intestine; 

 3, ovary; 4, uterus; 5, vagina; 6, genital pore; 7, excretory tube; 8, excretory pore. 

 (A, after Vogt and Yung; B, after Shipley and MacBride.) 



This phylum is likely to prove confusing to students as there are 

 various systematists who classify threadworms under different phyla 

 and under groups which they call "uncertain." 



Nematodes form the single class of Nemathelminthes, and the tw r o 

 best known forms used in the laboratory are Ascaris lumbricoides (Figs. 

 185 and 186), a parasitic worm found in the digestive tract of pigs, horses, 

 and man, belonging to the family Ascaridae; and Trichinelia spiralis 



