156 MANUAL OF ZOOLOGY SECT, vi 



uterus of the female, and the minute young (B, <?), to the 

 number of at least about a thousand, are born alive. Soon 

 after birth the young worms migrate through the walls of 

 the intestine and reach the voluntary muscles of the host, 

 such as those of the limbs, back, tongue, etc. Each worm 

 enters a muscle-fibre and coils itself up in the muscle- 

 substances (A) ; a spindle-shaped cyst (cy) is formed round 

 it, and the muscle undergoes more or less degeneration. 

 This process gives rise to various morbid symptoms in the 

 host, but, after some months the cysts become calcified and 

 the danger to the infected individual is over. In order that 

 further development of the encysted and sexless Trichinae 

 should take place, it is necessary for the infected flesh of 

 the host to be eaten by another animal in which the worm 

 is capable of living, e.g., that of man by pig or rat, or that 

 of a pig by man. When this is done the cysts are dissolved 

 by the digestive juices, the worms escape, develop repro- 

 ductive organs, and copulate, the young migrating into the 

 muscles and producing the disease as before. 



It will be noticed that in this case the parasite is able to 

 exist in various hosts, and that both sexual and asexual stages 

 are passed through in the same host, dispersal of the species 

 taking place by the flesh of an infected animal being eaten 

 by another, either of the same or of a different species. 



The female Guinea-worm {Dracunculus medinensis) attains 

 a length of 30-200 cm. (1-6 feet), and lives in the sub- 

 cutaneous connective tissue of man. The eggs develop in 

 the uterus, and the newborn young pass out of the body of 

 the host through abscesses caused by the presence of the 

 parasite. If, as must often be the case, they escape into 

 water, they make their way into the body of a water-flea 

 {Cyclops), and in this condition probably reach their human 

 host once more in his unfiltered drinking water. 



