!04 



CCELHELMTNTHES. 



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

 htematuria). 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. Mermithid.e. Elongate nematodes with six oral papillae. 

 They live in the body cavity of insect.s and pass into damp earth, veherethey 

 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 larv<B live in insects, 

 there being in some cases at least an alterna- 

 tion of hosts. Tliese (and the Mermithidae) are 

 popularly believed to be horse hairs changed 

 into worms. Gordius* Chord odes* 



Near the Gordiacea must be mentioned the 

 marine Sectonema * the young stages of which 

 y 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 Ascaridie (p. 301), but are easily 

 distinguished by the proboscis, which maybe 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 lemnisc 



beside 



Ftg. 371. — Male EchinorJn/n- 

 ckiis angusiatus. (From 

 Hiitschek.) b, penis sue ; 

 df'^ semmal vesicle; di\ 

 glands; g, sanglion; /, lem- 

 nisei; li'U ligament; m iWj, 

 r('tr;ictors of jiiMhoseis 

 und its sheatli ; p. iienis; 

 r, proboscis; j.s, prol)oscis 

 stieath; (, testes; vd, vas 

 deferens. 



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 Ecldn- 

 orhyiichiis ((jiga)itofhyclnis) gigas* of the pig 

 lives in the larva of the ' -Tune bug' (2Molontha), 

 that of E. proteiis of European fresh-water fishes 

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

 tremely rare in man. 



