PLATYHELMINTHES. FLAT-WORMS 27 



Since the Turbellaria have little if any economic importance they 

 will not be further discussed. 



The Cestodes or tapeworms, Fig. 20, are found in the digestive 

 tracts of vertebrates. Naturally those found in man are of the most 

 interest and importance. There are at least two large tapeworms 

 parasitic in man: Tania saginata, the unarmed, beef, or fat tapeworm, 

 the commonest form, and T. solium or pork tapeworm. The former 

 is taken into the body by eating imperfectly cooked beef; the latter 

 by eating imperfectly cooked pork. The latter is the more dangerous 

 but, according to Osier, is very rare in the U. S. The former is found 

 practically everywhere and though unpleasant is not necessarily very 

 serious. 



The life-history of T. saginata is briefly as follows: the adult worm 

 lives in the intestine of man; usually only one worm is found in an 

 individual, but as many as 59 have been reported. The worm has 

 a small head, about 2 mm. in diameter, Fig. 20, B, with four suckers 

 but without the circle of hooks that is found in T. solium and that is 

 shown in the figure. Following the head or scolex is a slender neck, 

 the segments of which gradually enlarge toward the posterior end 

 until, in the main body of the animal, they may be i cm. wide and 2 

 or 3 cm. long. There may be 1000 or more segments or proglottids 

 in a large worm, totaling a length of 20 or 30 feet. Each of the pos- 

 terior segments is a complete animal sexually, and they are con- 

 stantly breaking off and passing to the exterior with the feces. 



In ridding a patient of tapeworm by the use of purgatives it is 

 necessary to cause the extrusion of the entire worm, for if the scolex 

 remain attached to the intestine the segments will be rapidly re- 

 generated, at the rate, perhaps, of a dozen a day, so that the worm 

 will soon regain its normal size. 



It is estimated that a single worm may produce 150,000,000 eggs 

 per year; these, together with entire proglottids, are passed to the 

 exterior and may be taken into the digestive tract of a beef with 

 grass or in drinking water. While still in the proglottids the eggs 

 are fertilized and develop into tiny embryos. These embryos if taken 

 into the intestine of a beef burst out of their containing shells, bur- 

 row through the digestive walls of their second host and become 

 encysted, as tiny bladder-shaped worms known as cysticerci, or 

 bladder worms, in the muscles, especially in the tongue and chewing 



