344 



NEHATHELMINTHES. 



pliala they are branching subcutaneous canals. With a few excep- 

 tions the Nemathelminthes have separated sexes, and develop 

 directly without metamorphosis. The larvae and sexual animals are 

 not unfrequently distributed in two different hosts. 



The majority of the Nemathelminthes 

 are parasites either during the whole period 

 of their life or at different stages. There 

 are, however, also free living forms which 

 often show the closest relationship to the 

 parasitic members of the group. 



Order 1. NEMATODA (THREAD-WORMS).* 



Nemathelminthes, with mouth and ali 

 mentary canal. They are principally 

 parasites. 



The Nematodes possess an extremely 

 elongated thread-like body, which may be 

 provided with papillae at the anterior pole 

 in the region of the mouth, or with hooks 

 and spines within the oral cavity. The 

 mouth leads into a narrow esophagus, 

 which usually has thick muscular walls, a 

 chitinous lining, and a triangular lumen, 

 and is frequently dilated behind to a 

 muscular bulb (pharynx). In certain 

 genera (Rhabditis, Oxyuris), the chitinous 

 lining of the pharynx is raised into ridges 

 or tooth-like prominences, to which the 



* Besides the older writings of Rudolphi, 

 Bremser, Cloquet, Dujardin, compare Diesing, 

 " Systema helminthum," 2 Bde Wien, 1850-51. 

 Diesing, " Eevision der Nematoden," Wiener 

 Sitzungsberichte, 1860. Claparede, "De la for- 

 mation et de la fecondation des oeufs ehez les 

 vers Nematodes," Geneve, 1856. A. Schneider, 

 " Monographic der Nematoden," Berlin, 1866. 

 R. Leuckart, " Untersuchungen iiber Trichina 

 spiralis," Leipzig and Heidelberg, 1866. 2nd 

 edition ; also " Die menschlichen Parasiten," etc., 



FIG. 279. Oxyurit vermicularit 

 (after R. Leuckart). a, female ; 

 0, mouth ; A, anus ; V, genital 

 opening ; b, male with curved 

 posterior end; c, the latter 

 enlarged ; Sp , spiculum ; d, 

 egg with enclosed embryo. 



Tom. II., Leipzig and Heidelberg, 1876. C. Glaus, 

 " Ueber Leptodera appendiculata," Marburg, 

 1868. 0. Butschli, <; Untersuchungen iiber die 

 beiden Nematoden der Periplaneta orientalis," 

 Zeitzsclir. fur Wiss. Zool., Tom. XXL, 1871. And "Beitrage zur Kenntniss 

 des Nervensystems der Nematoden." Archir. fur Milir Anatomic, Tom X. 



