Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0101clau Year: 1884 XEMATODA. 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 (tig. 279). Its walls are formed of cells and are non-muscular, except behind, where they have a special investment of muscular fibres which rend
Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0101clau Year: 1884 XEMATODA. 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 (tig. 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 Gordius 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, , 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
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