WORMS, ROTIFERS, LEECHES, POLYZOA 77 



the head of the Tape-worm are developed, and on their escape, by 

 the death of the host or by its being eaten by another animal, 

 will become Tape-worms in the devourer. Thus the pig and the 

 ox are the intermediate hosts for two Tape-worms commonly 

 found in man, which develop in him as the result of eating the 

 raw or only partially cooked flesh of infected animals. The so- 

 called " measles " in pork is one stage of a disease produced by 

 the encystment of the embryo or cysticercus of a Tape-worm, and 

 if used for human food, unless submitted to prolonged and very 

 thorough cooking, would certainly infect the consumer with this 

 horrible parasite. 



A Tape-worm that is parasitic in the cat passes its cysticercus 

 stage in the liver of rats and mice, thus frequenting a situation 

 highly favourable for its transference to the final host. Others, 

 again, parasitic in birds, pass their cysticercus stage in the bodies 

 of earthworms, frogs, snails, and water-fleas (Cyclops). 



The Thread-worms (N ematoidea) are a group of round worms, 

 mostly parasitic in habit, and usually possessed of a mouth, a 

 swollen gullet, and a straight digestive canal. The cylindrical 

 body is generally very long in comparison to its width. One of 

 the most terrible parasites of man is a Nematoid worm called 

 Trichina spiralis. In the adult or sexual condition it lives in 

 the intestine of man, the pig, and other mammals. From the 

 female worm, after impregnation, escape a vast swarm of minute 

 young, which soon migrate through the walls of the intestine, 

 reaching the voluntary muscles of the host, such as those of the 

 tongue, back, and limbs. In this situation each worm enters a 

 muscle-fibre, coils itself up in the muscle substance, becomes en- 

 closed in a cyst, and the muscle undergoes more or less degenera- 

 tion. If further development of the encysted and sexless Trichina 

 worms is to take place, it is necessary for the infected flesh of the 

 host to be devoured by another animal in which the worm is cap- 

 able of living, e.g. that of a pig by man, that of man by a pig or 

 a rat. If this is accomplished, then the cysts are dissolved by the 

 digestive juices, the worms escape, develop reproductive organs 

 copulate, - nd the resulting young once again migrate into the 

 muscles of the host, producing the disease as before. 



Cobbold, who made a special study of these parasitic worms, 

 demonstrated the enormous number of Trichinse it is possible 



