422 ANIMALS INTRODUCED UNAWARES 



(Bothriocephalus latus], parasites of the food-canal of man, 

 have been carried far and wide. Round-Worms, including 

 the Maw Worm (Ascaris lumbricoides}, the common Oxyuris 

 vermicularis, the Miner's Worm (Dochmius (Ancylostomum) 

 duodenale], the Whip Worm (^Trichocephalus dispar\ and 

 the Pork Thread Worm ( Trichinella spiralis], have become 

 cosmopolitan. 



The kind of way in which many of these noxious in- 

 festations have spread in times past is still well illustrated 

 in the case of a dangerous parasite of the blood-vessels 

 of man Bilharzia haematobia. This species, which is 

 swallowed by man in impure drinking water, occurs over 

 Africa from Egypt to the Cape of Good Hope, and it has 

 been found that Mecca is a permanent centre of dispersal, 

 whence Mohammedans, returning from their pilgrimages, 

 carry the parasite to widely distant parts of the Old World. 



PARASITES OF LIVESTOCK 



The introduction of domestic and other animals from 

 foreign lands has also been the means of bringing a varied 

 and undesirable assemblage of aliens into our country. Like 

 man, these too have their external and internal parasites, 

 their temporary and permanent hangers-on. Without the 

 presence of the Pig, man would escape the Pork Tape- 

 Worm (Taenia solium\ and the Pork Thread- Worm (Tri- 

 chinella spiralis], for these find a temporary host in the 

 domestic animal, (as many as 12,000 to 15,000 of the latter 

 having been counted in a gramme of muscle). But wherever 

 the Pig has gone they have accompanied it. 



The Round- Worm of the Horse (Ascarismegalocephala), 

 a creature sometimes 17 inches long, often found in great 

 numbers ; the Tape-Worm fauna of the Dog's interior, 

 which includes at least a dozen distinct species ; the Liver- 

 Flukeof the Sheep {Fasciolahepatica}\ the Beef Tape-Worm 

 (Taenia saginata\ whose intermediate host is the Ox ; and 

 many other internal parasites of domestic animals, Tape- 

 Worms, Round-Worms and " Flukes " have been carried 

 wherever civilization has penetrated with its domestic stock. 



