304: 



C(ELIIELMTNTHES. 



through the kidneys, where they produce serious disturbance (albuminuria, 

 haematuria). There is possibly a connexion between them and elephanti- 

 asis. 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. MERMITHIDTE. Elongate nematodes with six oral papillae. 

 They live in the body cavity of insects and pass into damp earth, where they 

 become sexually mature. They share with the Gordiacea the common 

 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 epithelium ; 

 the intestine is supported by mesenteries; there 

 is an oesophageal nerve ring and unpaired ven- 

 tral nerve cord, and the female genitalia enter 

 the cloaca. The adults live in water, where 

 they lay their eggs; the larvaa live in insects, 

 there being in some cases at least an alterna- 

 tion of hosts. These (and the Mermithida?) are 

 popularly believed to be horse hairs changed 

 into worms. Gordius,* Chordodes* 



Near the Gordiacea must be mentioned the 

 marine Nectonema,* the young stages of which 

 are apparently passed in the mosquito. 



Order III. Acanthocephala. 



The species of spine-headed worms live in the 

 alimentary canal of vertebrates. In appearance 

 they resemble the Ascaridae (p. 301), but are easily 

 distinguished by the proboscis, which may be re- 

 tracted by muscles and exserted by contraction of 

 the muscular body wall. This proboscis bores into 

 the intestinal wall and is held in place by numer- 

 ous retrorse hooks (fig. 271). In internal anatomy 

 the entire absence of an alimentary canal marks 

 them off from Nematodes and Gordiacea, as also the 

 peculiar structure of the reproductive organs and 

 a closed vascular system in the body wall which 

 extends into two sacs, the lemnis.cS, lying beside 

 the proboscis sheath. The unpaired ganglion lies 

 on the proboscis sheath between the lemnisci. An 

 intermediate host occurs in development, the larva 

 living in an arthropod. Thus the larva of Ecliin- 

 orhynchus (Gigantorhychus) gigas* of the pig 

 lives in the larva of the ' .Tune bug' (Melolontlia), 

 that of E. proteus of European fresh-water fishes 

 in Crustacea. One species, E. hominis, is ex- 

 tremely rare in man. 



.-<* 



FIG. 271. Male Ectiinorhyn- 

 ckus angustatus. (From 

 Hatschek.) b, penis sac ; 

 de, seminal vesicle; dr, 

 glands; gr, ganglion; /Jem- 

 nisei; lig, ligament; mim ? , 

 retractors of proboscis 

 and its sheath ; p, penis ; 

 r, proboscis ; rs, proboscis 

 sheath; t, testes; vd, vas 

 deferens. 



