282 DARWINISM AND THE PROBLEMS OF LIFE 



mouth) of its master^ — the large vesicle is formed in 

 the muscles, generally in the liver, but sometimes in 

 the brain. Death follows in most cases. 



Thus the Tcznia echinococcus and the Tania solium 

 are found in man in the shape of scolices, and these 

 particular tape-worms are accordingly to be dreaded. 

 Another parasite of the human intestine is the broad 

 tape-worm, the Bothriocephalus latus, which grows to 

 a length of thirteen yards. We have referred pre- 

 viously to its migration. Differently from the tcenia, 

 it develops from the t%^ a larva that enters a fish, 

 if it reaches water, and incapsulates itself, without 

 forming a vesicle. It at once forms the head of the 

 future tape-worm, which develops in a new host that 

 has eaten the fish. Human beings get the worm by 

 eating underdone pike or turbot. 



This kind of migration brings us to the other 

 parasitic platodes, the suctorial worms. They are 

 rarely found in man, and are never dangerous — in 

 Europe, at all events.^ But they are a great plague 

 to other animals, such as sheep, birds, and frogs. 

 The fluke or gourd-worm, shaped like the kernel of 

 a gourd, the Distomum kepaticum, is found in the 

 sheep's liver, or rather in its gall-duct. Its eggs pass 

 by the gall-duct into the gut, and then out with the 

 excrements. If they fall into water, minute, lancet- 



^ People should, therefore, be careful with dogs. They should at 

 least wash their hands after touching them, and should never let dogs 

 kiss them. 



^ In Egypt the Bilharzia hmmatobia is one of the most dangerous 

 parasites. It lives in the human blood-vessels, especially the portal 

 and urinary veins. 



