CHAPTER XXV 



THE THORN-HEADED WORM. THE LEECHES 



Order II. Acanthocephala. Nemathelminthes (p. 216). — Essential 

 differences separating this order from the Nematoda are the absence of 

 a digestive tube and the possession of a protractile rostrum provided 

 with hooks. The body cavity contains a fluid in which are the sexual 

 organs. The sexes are separate. 



One species is of sufficient pathologic importance for consideration. 

 This is the large intestinal roundworm of the hog, Gigantorhynchus 

 hirudinaceus of the family Gigantorhynchidse, more commonly described 

 under the name Echinorhynchus gigas. 



Gigantorhynchus hirudinaceus (Echinorhynchus gigas). Fig. 165. 

 Acanthocephala (p. 306). — The body is white, cyhndrical, transversely 

 wrinkled, and often expanded at several points. The rostrum is almost 

 globular, retractile, and has five or six rows of backward-curving hooks 

 (Fig. 166). The caudal extremity is somewhat tapering. The males 

 are smaller and thinner than the females and have a bell-shaped caudal 

 bursa. The caudal extremity of the female is rounded. 



The female is 20-35 cm. (8-13 inches) in length by 4-9 mm. (5/32- 

 11/32 of an inch) in breadth. The male is 6-10 cm. (2 3/8-4 inches) in 

 length and in breadth 3-5 mm. (1/8-7/32 of an inch). 



The eggs are oblong, measuring 87-100 microns. When developed 

 they are surrounded by three envelops. The embryos are formed within 

 the body of the female. 



The adult worm is parasitic in the small intestine of the hog; excep- 

 tionally it occurs in man. The larva lives encysted in the white grub 

 of the May-beetle and probably some other invertebrates. 



The eggs of Gigantorhynchus, discharged to the ground with the 

 feces of the hog and eaten by the larva of the May-beetle, are hatched 

 in the digestive canal, and the embryos, by burrowing through the in- 

 testinal wall, find their way into the body-cavity where they become 

 encysted. In this state they may continue to live through the larval 

 and pupal stages and even after the maturity of the insect. If the hog 

 eats the May-beetle in any of these stages containing the cyst, the cyst 

 wall is digested away and the freed larval worm attaches by its cephalic 

 hooks to the intestinal mucosa where it attains full development. 



Occurrence, Pathogenesis and Symptoms. — The giant intestinal 

 worm of the hog is quite common in the United States, especially so in 



