Il6 SYSTEMATIC ZOOLOGY 



eating insufficiently cooked fish. The scolex is flattened and 

 provided with two suckers and no hooks ; the worm may be 

 about one centimeter broad and may attain a length of twelve 

 meters, possessing several thousand proglottides. The proglot- 

 tides are readily distinguished from those of the other human 

 tapeworms by the dark markings on the side, due to the con- 

 tained eggs (Fig. 103). The most common tapeworm in man is 

 Tcenia solium{ Fig. 104), or the pork tapeworm, so called because 

 the cysticercus lives in pigs ; it is most frequent in countries where 

 raw or partially cooked pork is eaten. The scolex is provided 

 with four suckers and a circle of hooks, and each proglottis 

 is provided with a genital pore on one margin. The proglot- 

 tides resemble those of the beef tapeworm, Tcenia saginata, 

 whose cysticercus lives in cattle, and insufficiently cooked beef 

 is the cause of infection. The scolex has four suckers and no 

 hooks (Fig. 105), and the proglottides, if rendered transparent, 

 can be distinguished from those of Tcenia solium by the branch- 

 ings of the egg-filled uterus ; in the pork tapeworm these are 

 large and few, in the beef tapeworm they are fine and numerous 

 (Fig. 106). Tcenia solium may attain a length of three and a 

 half meters, with eight or nine hundred proglottides less than a 

 centimeter broad. Tcenia saginata, of about the same width, 

 may become seven or eight meters long with twelve hundred to 

 thirteen hundred proglottides. Other tapeworms may occur in 

 man, but these are the most common. Cysticerci are also some- 

 times human parasites, and the most important of these is the 

 cysticercus of the Tcenia echinococcus of the dog. The adult is 

 very small, less than half a centimeter long and with usually 

 only three proglottides. The embryos may enter the human 

 body through the handling or kissing of infected dogs, or by 

 similar unhygienic practices. They have been found in the 

 lungs, liver, brain, and other organs, and sometimes produce 

 tumors of great size and weight. 



SUBTYPE II. NEMERTINA 



The Nemertina (Gr. N^e/OT^s, name of a Nereid) or ribbon 

 worms were for a long time classified with the Platyhelminthes, 

 for the body is usually more or less flattened, but in several 



