NBMATODA. 



275 



a 



and is frequently dilated behind to a muscular bulb (pharynx). In 

 certain genera (Rhdbditis, Oxyuris), the 

 chitinous lining of the pharynx is raised 

 into ridges or tooth-like prominences, to 

 which the radial muscles converge in the 

 form of conical bundles. According to 

 its function, the oesophagus is essentially 

 a suctorial tube, which pumps in fluids, 

 and by peristaltic action passes them on 

 to the intestine. The intestine follows 

 the pharynx, and opens by the anus not 

 far from the hind end of the body on 

 the ventral surface (Fig. 226). Its walls 

 are formed of cells and are non-muscular, 

 and are coated with cuticle both inside 

 and outside ; it may be reduced to a row 

 of perforated cells (Filaria). The ter- 

 minal portion, or rectum, has a special 

 investment of muscular fibres which 

 render it contractile. Muscular fibres 

 passing from the body-wall to the Avail 

 of the rectum are also frequently present. 

 In certain Nematodes the anus may be 

 wanting (Mermis) ; and in some genera 

 (see p. 290) even the alimentary canal 

 undergoes degeneration. 



Beneath the stiff cuticle, which is often 

 transversely ringed and is composed of 

 several layers, lies a soft granular nu- 

 cleated sub-cuticular layer (Tiypodermis\, 

 which is without cell limits and is to be 



-, , ., , FIG. 226. Oxyuris vermicularis 



regarded as the matrix of the former. (after K . L euckart). a, female ; 

 Beneath this lies the highly -developed mouth; A a " us ; v genital 



opening, b, male with curved 



muscular layer, which consists of band- posterior end. c, the latter en- 

 shaped or fusiform longitudinal muscles, largert ; s p spicuium. d, egg with 



enclosed embryo. 



The surface of the body may present 



markings, as for instance polyhedric spaces and longitudinal ribs, 



also processes in the form of tubercles, spines,* and hairs. Ecdyses, 



There may also be prominences of various kinds, and even in some cases a 

 complete covering of spines (Cheiracanthu-s Dies. = Gnathostoma Ow. , Ch, 

 hispidum Fedsch. ). 



