THORN-HEADED WORM 



663 



plies, a large worm. The female often reaches a length of 8 to 12 

 inches; the male, 3 to 4 inches. The fully developed worm 

 is about as large around as a good-sized lead-pencil at its anterior 

 extremity, and tapers somewhat posteriorly. At the posterior 

 end the female parasite is only about as large as an ordinary knit- 

 ting needle. The male parasite does not taper as markedly as the 

 female. This worm is of a milky white color, and shows on the 

 surface of the body a number of 

 transverse ridges. 



At the anterior extremity of the 

 worm there is a very abrupt taper- 

 ing off to form the head. This head 

 is armed with a powerful biting 

 stylet or proboscis, by means of 

 which the worms attach themselves. 

 On each side of this proboscis is a 

 bristling row of small hooklets which 

 under a large reading glass very 

 closely resemble the claws of a cat. 

 This parasite has no digestive ap- 

 paratus as in the case of the round- 

 worm, but absorbs its food from the 

 digested contents of the intestine of 

 its host. 



Mode of Infestation. — The manner of infestation of hogs with 

 this parasite forms a somewhat different story from that seen in the 

 case of the common round-worm and the whip-worm. The male 

 and female worm breed in the intestines of the hog, and the female 

 develops a large number of eggs, which are laid in the bowel and 

 pass out with the bowel contents. These ova or eggs are micro- 

 scopic in size, being about ^^^ inch long, and can be seen only with 

 a powerful magnifying lens or a microscope. 



These eggs pass out to the ground, and are there eaten by the 

 common white grubworm, which is the larval form of the May 

 beetle or May bug. In the digestive tract of the grubworm the 

 eggs hatch in a very few days and liberate the young, imperfectly 

 developed parasite, which is the forerunner of the giant thorn- 

 headed parasite afterward to be found in the bowel of the hog. 



Fig. 92. — Echinorhynchus 

 gigas, female: a, Globe-shaped 

 proboscis, armed with six rows 

 of hooklets; b, tail extremity. 

 (From Kaupp's Animal Para- 

 sites.) 



