NEMATODA. 



345 



radial muscles converge in the form of conical bundles. Accord- 

 ing 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. 279). Its walls are formed of cells and are non-muscular, 

 except behind, where they have a special investment of muscular 

 fibres which render the terminal portion contractile. Muscular 

 fibres passing from the body wall to the wall of the rectum are also 

 frequently present. In certain Nematodes the anus may be want- 

 ing (Mermis) ; and in Gfordius even the alimentary 

 canal undergoes degeneration. 



Beneath the stiff cuticle, which is often trans- 

 versely ringed, and is composed of several layers, 

 lies a soft granular nucleated sub-cuticular layer 

 (hypodermis), which is to be regarded as the matrix 

 of the former. Beneath this lies the highly deve- 

 loped muscular layer, in which band-shaped or fusi- 

 form longitudinal muscles predominate. The surface 

 of the body may present markings, as for instance 

 polyhedric spaces and longitudinal ribs, also pro- 

 cesses in the form of tubercles, spines,* and hairs. 

 Ecdyses, i.e., shedding the cuticular layer, seem 

 only to occur in the young forms. The muscles 

 are each composed of a single cell, in which two 

 parts are distinguishable, a clear, sometimes a 

 granular protoplasmic portion (medullary sub- 

 stance), which projects into the body cavity and 

 is often prolonged into processes ; and an external 

 fibrillated layer (fig. 280). The Nematodes may 

 be distinguished as Meromyaria or Polymyaria, 

 according to the arrangement of their muscular system. In the 

 Meromyaria the number of muscle cells (which are arranged 

 according to definite laws) in the cross section is small (eight), 

 while in the Polymyaria their number is considerable. In the latter 

 the muscle cells are often connected together by transverse processes 

 of the medullary substance, which unite on the so-called median 

 lines to form a longitudinal cord. 



* There may also be prominences of various kind?, and even in some cases a 

 complete covering of spines (Cheiracantkus Dies = Gnathostoma Ow., Ch. 

 hispidum Fedsch.) 



FIG. 280. Muscle- 

 cell of ANematode. 



