PHYLUM NEMATHELMINTHES 289 



imber of at least a thousand, are born alive. Soon after birth 

 young worms migrate through the walls of the intestine, and, 



llowing the course of the connective-tissues, reach the voluntary 



mscles of the host, such as those of the limbs, back, tongue, etc. 



ach Worm then penetrates the ^af coj^mrn,a of a muscle-fibre and 

 coils itself up in the muscle-substance (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. The flesh of a " trichi- 

 nised" human subject has been estimated to contain 100,000,000 

 encysted worms, and that of an infected pig 85,000 to the ounce. 

 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 a 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 reproductive organs, 

 and copulate, the young migrating into the muscles and producing 

 the disease as before. The result of eating an ounce of " trichi- 

 nised " or " measly " pork, improperly cooked, might be the 

 liberation in the human intestine of perhaps 8-0,000 worms, and, 

 if half of these were females, each producing 1,000 embryos, some 

 40,000,000 worms would shortly begin to migrate into the muscles, 

 and produce the various symptoms of " trichiniasis." 



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

 various hosts, and that both sexual a,nd 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 a different species. 



The female Guinea-worm (Dracunculus medinensis) attains a 

 length of 30-200 cm. (1-6 ft.), and lives in the subcutaneous 

 connective-tissue of Man. The eggs develop in the uterus, and 

 the new-born 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 jn his unfiltered 

 drinking-water. v 



CLASS IL-ACANTHCCEPHALA. 



This class contains a few genera of parasitic worms, of which EchinorJiynchu* 

 is the chief. The present section will be devoted to this genus,, a not uncommon 

 parasite in the intestine of Mammals, Birds, Reptiles, Amphibians, and Fishes. 

 The largest species, E. gigas, is found in the Pig (Fig. 235, A), and has once 

 been recorded in the human subject : it may attain, in the female, a length of 50 

 cm., or more than half a yard. Most species are small,\not exceeding 1 cm. in 

 length. 



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