Not all tapeworms are divided into segments like 

 the typical forms. There are undivided ones, which 

 look more like flukes, but the distinction is not as 

 fundamental as was once thought, and the two sub- 

 classes are based on other characters. The subclass 

 Cestodaria includes forms with an undivided body 

 and a ten-hooked larva, that live in the body cavity 

 and intestine of lower fishes. The subclass Eucestoda, 

 in which the larva has six hooks, comprises a few 

 undivided forms and all the typical segmented tape- 

 worms, including those few described here. 



The beef tapeworm, Taenia saginata, maintains 

 its place in the human intestine, despite the constant 

 movement of materials in that active organ, by means 

 of four suckers on the scolex. As in many other tape- 

 worms, the male sex organs start to grow first and 

 appear most prominent in the younger segments; 

 both sets of organs are well developed in middle seg- 

 ments; and toward the most mature region the seg- 

 ments are nothing but little bags stuffed with eggs 

 that have already begun to develop into embryos. 

 The fully ripe segments, loaded with embryos, de- 

 tach from the worm and pass out with the feces onto 

 the ground or onto vegetation. As cattle graze they 

 may ingest shelled embryos, and in the bovine intes- 

 tine the eggshell is digested off and the six-hooked 

 embryo is released to burrow its way through the in- 

 testinal wall and into a blood vessel. Carried by the 

 blood to the muscles, the embryo remains there and 

 grows into a sac or bladder which sprouts from its in- 

 ner wall the inverted future head of the tapeworm. 

 When man eats raw or undercooked beef the enclos- 

 ing bladder is digested oflF, and the head everts and 

 attaches to the human intestinal wall by means of 

 the suckers. 



Meat inspection has greatly reduced the incidence 

 of beef tapeworms in Western countries; but though 

 the bladders of this tapeworm are almost Vi of an 

 inch long, they can easily be overlooked in the rou- 

 tine inspection of the jaw muscles and the heart, the 

 parts of the cow usually examined by official meat 

 inspectors. It is best to avoid raw or seriously under- 

 done beef. Where sanitation is poor, as in Africa, or 

 in countries where meat is broiled in large chunks, 

 much of the population is infected. Among the Hin- 

 dus of India, who have religious restrictions against 

 eating beef, a diagnosis of beef tapeworm may be 

 embarrassing to the patient; or when due to mistaken 

 diagnosis through confusion with other tapeworm 

 eggs that show six hooks, it can be deeply insulting to 

 the patient as well as rather embarrassing to the 

 physician. 



The pork tapeworm. Taenia solium, which has a 

 crown of hooks on the scolex in addition to the suck- 

 ers, is likewise rare among Jews and Moslems. 

 Though the bladderworms are common in pigs, the 

 adult in humans is rare in the United States, more 



common in parts of Europe where pork is eaten with- 

 out thorough cooking. 



The largest and most injurious tapeworm that par- 

 asitizes man is the broad fish tapeworm, Dibothrio- 

 cephalus latiis (formerly Dipliylloholhriiini latum), 

 a monster up to 55 feet long, with three to four thou- 

 sand segments. In man it usually averages from 15 to 

 20 feet long. For centuries it has infected central Eu- 

 rope, and now occurs in 20 per cent of Finns and al- 

 most 100 per cent of the population of certain Baltic 



The circlet of hooks on the scolex of the dog tape- 

 worm. Taenia pisiformin, as seen by darkfiekl photo- 

 micrography. (Montana. W. C. Marquardt) 



areas. It may be found also in such places as Ireland, 

 Palestine, Uganda in Africa, Siberia, Japan, and 

 Chile. In North America it is known from Michigan, 

 Minnesota, Wyoming, Manitoba, Alaska, and even 

 Florida. Long thought to have been brought to the 

 Great Lakes region by lumbermen from northern 

 Europe, this tapeworm may also have come with 

 Asians over the Bering Straits; or it may have been 

 well established in fish-eating wild carnivores, like 

 the brown bear, before man's arrival. In addition to 

 man and the bear, it has been reported also in the 

 dog, cat, fox, and others. The life history involves 



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