//. NEMATHELMINTHES : NEMATODA. 



anlagen of sexual organs. To attain this it must be transported into the 

 intestine of another host, ^hen, for instance, man eats trichinosed pork 

 the worms are freed from the muscle and capsules by the digestive 

 fluids and, entering the small intestine, become sexually mature in a few 

 days. The female (3-4 mm. long, the male 1.5 mm.) penetrates into the 

 superficial layer of the intestinal villi and in course of a month gives birth 

 to 1500 (some say 10,000) living young, after which she dies. The young, 

 on the other hand, penetrate the lymph vessels, and by way of the 

 thoracic duct are carried into the blood-vessels, and wander from the 

 capillaries into the muscles, especially those which are much worked, like 

 the diaphragm, eye muscles, and muscles of the neck, and which conse- 

 quently have a rich blood supply. They enter the sarcolemma of the 

 muscle, destroy the muscle substance, and finally become enclosed by a 

 capsule secreted by the host. The wandering takes place about the second 

 or third week after infection, the encystment in about three months. A 

 slight infection causes disagreeable symptoms ; but where large numbers 

 obtain entrance the cases are frequently fatal. The worst epidemic known 

 was in Emmersleben, Saxony, in 1884, where 57 died in four weeks from 

 infection from one pig. 



FIG. 270. Transverse section of young Gordius. (After von Linstow.) a, hypoder. 

 mis; b, muscular layer; c, cuticle; d, parenchyma; e,/, muscles and mesenteries; g, 

 alimentary canal ; ft, nervous system. 



Family 5. FILARIID.E. These are extremely elongate, hair-like worms. 

 Their best-known representative is Dracunculus medinensis, the guinea 

 worm (the female about a yard long, and about as large as stout packing 

 twine), which produces a sickness known to the Greeks as dracontiasis. It 

 forms abscesses beneath the skin in which the worm is coiled up. The em- 

 bryos break through the wall of the mother and must enter the water and 

 penetrate a small crustacean, Cyclops. It is apparently introduced into 

 the human system by swallowing the Crustacea with drinking water. The 

 worm has recently been found in the tropics of America. 



A second species is Filaria sanguinis hominis, the adults of which 

 3 to 6 inches long live in the lymphatic glands of man, while the young 

 escape into the blood, often in immense numbers. They often escape 



