338 ORGANS OF DrGESTION. 



class, and in the higher forms of articulata. The distoma 

 hepaticum is like a more highly organized segment of a tcenia, 

 in which we perceive a broad funnel-shaped oesophagus lead- 

 ing to two wide ramified alimentary canals occupying the 

 middle part of the body, while the ovaries here occupy the 

 sides, and two parallel ventral nervous filaments unite below 

 the oesophagus and ramify as they extend around that wide 

 passage. In the echinorhynchus there is a minute pore in the 

 centre of the armed head, which leads to a single alimentary 

 canal extending along the middle of the trunk and dividing, 

 before it terminates, as in the other parenchymatous worms. 



In all the nematoid and more perfect forms of entozoa the 

 alimentary canal passes simple through the body, presenting 

 a distinct oral and anal aperture which are generally at the 

 opposite ends of the trunk, as in the higher articulata. The 

 ascaris, like the other nematoid worms, has a single oral 

 aperture at the anterior extremity of the body ; the three 

 marginal lobes of the mouth are provided with minute teeth 

 and moved by distinct muscles, so that the mouth somewhat 

 resembles that of the leech in its masticating apparatus. 

 The oesophagus forms a wide elongated muscular sac, like 

 that seen in the halithea and some other annelides ; it is con- 

 tracted at its lower part, and opens into a straight and wide 

 intestinal canal with thin parietes, and where the limits of 

 the stomach are seldom indicated by an inferior constriction. 

 The digestive canal passes straight through the middle of the 

 trunk, surrounded by the tubular windings of the testicle or 

 ovaries, to the posterior extremity where it opens by a small 

 traverse aperture on the inferior surface. In the strongytus 

 armatus (Fig 1 16. D.) the hemispherical disk of the head is 

 surrounded by dense, sharp, vertical teeth (D. a.), and the 

 short oesophagus (D. c.) opens into a wide intestine (D. d.) 

 without a distinct gastric portion and continued straight 

 through the trunk to the anus (D. e.) at the opposite end 

 of the body. The two long convoluted ovaries (D. h. h.) 

 wind round the alimentary canal in its whole course through 

 the trunk in the female, and unite to form a single vaginal 

 orifice (D. g.) below the middle of the body, the single 

 tubular testicle winds round the intestine in the same man- 

 ner in the male, and opens by a long projecting hollow 

 styliform organ of intromission at the posterior end of the 



