268 



CCELHELMINTHES 



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

 from one pig. 



Family 5. FILARIID.E. Extremely elongate, hair-like worms. Dracuncnliis 

 medinensis, the guinea worm (the female about a yard long, and about as large 

 as stout packing twine), produces abscesses beneath the skin in which the 

 worm is coiled up. The embryos break through the wall of the mother and 

 must enter the water and penetrate a small crustacean, Cyclops. It is appar- 

 ently introduced into the human system by swallowing the Crustacea with drink- 

 ing water. The worm occurs in tropical America. 



Filaria sanguinis hominis, 3 to 6 inches long, lives in the lymphatic glands of 

 man, the young escaping into the blood, often in immense numbers. They 

 often pass through the kidneys, where they produce serious disturbance. There 

 is possibly a connection between them and elephantiasis. The intermediate 

 host is apparently the mosquito. As yet they are known only in the tropics. 

 Other species occur in man and other animals. 



Family 6. MERMITHID/E. Elongate nematodes in the body cavity of insects; 

 they pass into damp earth, where they become sexually mature. They share 

 with the Gordiacea the name 'hairworms.' Mermis* 



Order II. Gordiacea. 



The hairworms resemble the nematodes in general appearance, but differ 

 greatly in structure. The body cavity has both splanchnic and somatic epithe- 

 lium; the intestine is supported by mesenteries (fig. 249) ; there is an cesophageal 



FIG. 249. Transverse section of young Gordius (after von Linstow). a, hypo- 

 clermis; b, muscular layer; c, cuticle; d, parenchyma; e, f, muscles and mesenteries; g, 

 alimentary canal; h, nervous system. 



nerve ring and unpaired ventral nerve cord, and the female genitalia open into 

 the cloaca. The adults live in water, where they lay their eggs; the larva? live 

 in insects, there being in some cases an alternation of hosts. They are popularly 

 believed to be horse hairs changed into worms. Gordius* Chordodes* Near 

 the Gordiacea must be mentioned the marine Nectanema,* young stages appar- 

 ently passed in the mosquito. 



Order III. Acanthocephala. 



The adult spine-headed worms live in the alimentary canal of vertebrates. 

 They resemble the Ascaridae (p. 266), but are easily distinguished by the pro- 



