WORMS IN THE INTESTINAL CANAL HELMINTHIASIS. 623 



similar to those of the taenia solium. They have the lateral sexual open- 

 ings, but the links are broader and thicker ; and the sexual organs are 

 more fully developed, and more branched than in the links of the 

 taenia solium. The difference in the head is more decided. The head 

 of the mediocanellata has neither snout nor the row of hooks, but is flat, 

 with four large suckers. This species has remained unknown so long, 

 because we rarely succeed in expelling the head, and it has been 

 customary when we found links where the sexual openings were on 

 the side, to consider them as cases of tagnia solium, and when the links 

 had the openings in the middle, to regard them as bothriocephalus 

 latus. 



The bothriocephalus latus, the broad tape-worm, resembles taenia, 

 but may readily be distinguished from it. In its head, instead of the 

 snout, the hooks, and suckers, we find only two lateral slit-shaped 

 fossae. The neck is scarcely to be seen. The breadth of the links is 

 much greater than the length ; they are about in the proportion of 

 three to one. The most important distinguishing mark between single 

 links of the two varieties is the position of the sexual openings. In 

 the bothriocephalus these are not to the side but in the middle of the 

 links, so that in them we may speak of a belly and back. The both- 

 riocephalus also inhabits the small intestine. It occurs in eastern Eu- 

 rope as far as the Vistula, and in Switzerland it is found with the 

 taenia solium. 



The ascaris lumbricoides, the round worm, is cylindrical, pointed 

 at both ends, from six to twelve inches long, and from two to three 

 lines thick. The body is so transparent that we may see the intesti- 

 nal canal, extending from one end to the other, and the sexual organs. 

 There is a circular depression behind the head ; the latter has three 

 small elevations, between which lies the mouth. The sexes are in 

 different individuals. In the female there are large ovaries and ovi- 

 ducts ; the male is smaller and somewhat crooked at its tail-end, which 

 contains the long, tortuous, seminiferous tubes and the testicles. At 

 the tail-end of the male we may see the hair-like, sometimes doubled, 

 penis. In the upper third of the female is a fissure six to eight lines 

 long, the opening of the sexual organs. The round worm inhabits the 

 small and large intestine, but makes excursions in various directions 

 and may enter the stomach, oesophagus, or even the larynx. From 

 the duodenum it occasionally makes it way into the ductus choledo- 

 chus. It does not seem probable that it can perforate the intestine ; 

 but if the intestine be perforated by any disease, we not unfrequentiy 

 find round worms in the cavity of the abdomen. They often occur in 

 incredible numbers. 



The oxyuris vermicularis, thread or maw-worm, is a small worm 



