ANATOMY OF THE NEMATODES 363 



INTESTINAL CANAL. The oral aperture, which is situated at the 

 tip of the anterior extremity, is frequently surrounded by thick lips, 

 or small bristles, or papillae ; it leads to a more or less strongly 

 developed buccal cavity, which is lined by a continuation of the body 

 cuticle, and which in some species is provided with " teeth," repre- 

 senting differentiated portions of the cuticle. 



THE CESOPHAGUS (fig. 262), which arises from the base of the oral 

 cavity, is as a rule a short, bottle-shaped tube with triradiate lumen ; 

 its wall is chiefly composed of radiating muscular fibres, which give 

 it the appearance of being transversely striped when viewed from the 

 surface. There exist also in its wall three large gland cells (ceso- 

 phageal glands) and nerves arising from the lateral lines and running 

 forward. The radial fibres cause a dilatation of the lumen, and 

 exercise an effect antagonistic to the elasticity of the cuticle lining 

 the inner surface. The latter has its own particular layer, which is 

 not in direct connection with that of the oral cavity. Special dilator 

 muscles, arising from the dermo-muscular tube and situated at the 

 commencement of the oesophagus, are only known in a few species. 

 The posterior end of the oesophagus presents a bulb-like dilatation, 

 and is frequently provided with small chitinous movable valves. In 

 a few forms, which belong to the Trichotrackelidce (Trichocephalus, 

 Trichinella), the oesophagus is a very long cuticular tube, beset on its 

 dorsal surface with a series of large nucleated cells. In others (Cucul- 

 lanus, Ascaris, etc.), a tube, the so-called glandular stomach, lined 

 only by epithelial cells, follows behind the muscular oesophagus. 

 This glandular stomach is, from its structure, easily distinguished 

 from the mid-gut, or chyle intestine, which is likewise cellular. The 

 so-called mid-gut is a tube lined by flat, cubical, or cylindrical cells 

 (fig. 260) surrounded by " isolation tissue " ; its transverse section is 

 circular or flattened dorso-ventrally ; the lumen may run in a straight 

 line, or it runs a sinuous course through the alternating prominences 

 of the then flat epithelial cells. 



The ectodermal hind gut s, as a rule, very short. At the anal 

 opening the cuticle and the subcuticular layers are reflected inwards, 

 forming the lining of the hind gut. In large species the subcuticular 

 tissue forms large cells on which anteriorly lie in addition large 

 " glandular cells." 1 n the male the ejaculatory duct opens at this 

 point. Around the end part of the gut, either on the chyle intestine 

 or at the beginning of the end gut, there exists a sphincter muscle 

 arising from a muscle cell which acts antagonistically to the two 

 diaphragm-like dilator muscle cells which stretch from the gut to the 



1 In Ankylostomes according to Looss these cells have no glandular function, but are 

 ligaments. 



