300 



ZOOLOGY 



SECT. 



of fine bristles running along either side of the elongated body. 

 A regular ecdysis or moulting of the cuticle at intervals takes place 

 in many Nematodes. The sub-cuticle in most cases takes the 

 form of a protoplasmic layer with scattered nuclei ; but in the 

 Nematomorpha (Fig. 250, ep.) it consists of a true epithelium a 

 single layer of cells the outlines of which are quite distinct. 



Beneath the ectoderm is a mus- 

 cular layer, which in many genera 

 has the same structure as in 

 Ascaris, i.e., consists of a single 

 layer of longitudinal fibres, inter- 

 rupted at the dorsal, ventral, and 

 lateral lines, each fibre being 

 spindle-shaped and produced into 

 a protoplasmic process which pro- 

 j ects into the body-cavity. But in 

 many forms (e.g., Strongylus) the 

 muscle-cells are flat rhomboidal 



Fia. 248. The body-wall of a platymyarian plates (Fig. 248), and each quad- 

 Nematode, spread out. lat. 1. lateral lines. * , -i , ,-, 



(After Leuckart.) rant contains only two rows, tne 



total number in a transverse 



section being therefore eight. In Gordius the muscles are inter- 

 rupted along the ventral line only (Fig. 250), and in Nectonema 

 only along the dorsal and ventral lines, the lateral lines being 

 absent. In Gordius, but not in Nectonema, the protoplasmic 

 portions of the muscle-cells are directed outwards, not inwards. 



Enteric Canal. The mouth is frequently armed with spines 

 (Fig. 249, C), by means of which the worms draw blood from the 



FIG. 249. Dochznius duodenalis. A, male and female in coitu. B, anterior end, 

 showing cv. gl. cervical glands ; ph. pharynx. C, mouth with spines ; D, posterior end 

 of male, with bursa. (After Leuckart.) 



intestinal blood-vessels of their host. Many free-living forms have 

 a sharp stylet for piercing the tissues of the plants on which they 

 feed, and a suctorial apparatus for absorbing the juices. The 

 posterior end of the oesophagus is often dilated to form a globular 



