76 WORMS, ROTIFERS, LEECHES, POLYZOA 



jointed bodies, narrow and small heads, usually armed with hooks 

 and suckers suited for clinging on, and gradually narrowing tail 

 end. They have no digestive system, but, living in the enteric 

 canal of their host, absorb the contained fluids through the general 

 surface of their body. 



A Tape-worm consists of a long ribbon made up of innumer- 

 able segments or proglottides, the long body narrowing at one 

 end into a rounded knob, the head or scolex. Upon the small 

 head a circlet of hooks, borne on a rounded prominence called 

 the rostellum, look like a little crown, and just behind are four 

 oval suckers arranged at regular intervals. The jointed body, 

 which may attain upwards of 20 yards in length, is generally 

 separated from the head by a slender neck, from which the pro- 

 glottides are segmented off, and become more individualised the 

 farther they recede from the neck by the development of younger 

 joints. All these proglottides in time develop sexual organs and 

 produce ova, and as they mature break off from the rest of the 

 worm, which still continues to grow. The head, or scolex, is 

 really an anchoring organ and a kind of nurse ; it is asexual and 

 buds proglottides, which are reproductive. The detached pro- 

 glottide has power of independent movement, so that it may either 

 pass out along with the evacuations of the first host or make its 

 escape by its own movements. In either case it will creep slowly 

 on to some moist object near at hand, such as the stalks of plants 

 and blades of grass, and is then devoured along with the herbage 

 by some vertebrate animal ; or should the proglottide fall into 

 water, it bursts there, and the liberated eggs are swallowed by 

 the animal drinking the infected water. In either case the eggs 

 arrive in the stomach of a new host. 



The embryos are minute, globular, naked vesicles, armed 

 with microscopic booklets, by means of which, should opportunity 

 present itself, they will bore inwards into the tissue of their host, 

 until finally the parasite reaches a small vein belonging to the 

 portal system, and thence is carried by the flow of blood into 

 the liver. Or, it may penetrate into other blood vessels and so 

 get carried by the general circulation along to some other organ, 

 to the brain, heart, or lungs. Wherever it finally becomes de- 

 posited it becomes encysted, and a new growth occurs, and by a 

 process somewhat like budding, one or more bodies resembling 



