^108. 



THE HELMINTHES. 



113 



this canal is simple, straight, and ends posteriorly in an anus.'^ In many 

 Trematodes, the intestinal tubes have in all their course simple or ramified 

 caeca, and in some, these caeca are so fully developed that the intestinal 

 canal appears to fill the whole body.'* The intestinal walls here are very 

 thin, but this does not prevent peristaltic and anti-peristaltic movements, by 

 which their contents move backwards and forwards, and are often rejected 

 through the mouth/^^ 



§ 108. 



In the Nematodes, and Gordiacei, the intestinal canal passes straight from 

 the mouth which is at the anterior extremity, through the cavity of the 

 body to the anus, which, in the first, opens front of the caudal extremity.^* 

 In very many Nematodes, the mouth has nodosities and swellings, but it is 

 seldom that its cavity has horny, tooth-like processes.*-' 



From the mouth extends a long and very muscular oesophagus, which is 

 usually dilated claviforra at its lower extremity. When the oesophagus iB 

 very long, it has one or more constrictions.*''' It is nearly always composed 

 of three longitudinal muscles which are united by longitudinal seams. The 

 triangular cavity circumscribed by these muscles is lined by a very firm 

 epithelium, which is sometimes horny, and in some species so thickly set in 

 the clavate dilatation that it resembles a masticatory apparatus.'*' The 

 intestine consists of a straight tube, with thin walls and without dilata- 



Gasterostomum ; and the species above men- 

 tioned I have discovered in the intestinal canal of 

 Perca Jluviatilis, and Lucioperca. 



7 See Miram, Owen, and Diesins, loc. cit. The 

 opening at the posterior extremity of many Trema^ 

 todes, and by many Helminthologists taken for an 

 anus, belongs to a special secretory organ, which 

 will be mentioned hereafter. 



S In many species allied to Monostomum tri^o 

 nocephalum, the two intestinal tubes have simple 

 caeca upon both sides of their entire length. In 

 Octobothrium lanceo/atum, the structure is the 

 same ; see Mayer, Beitr. p. 21, Taf III. fig. 3. 

 These lateral caeca are more or less ramified in Oc- 

 tobothrium palmatum , sa^ttatum, Merlan^i, 

 Poli/stomum appendiculatum, and Tristomum 

 elongatum {Leuckart, Zool. Bruchstucke, Hft. 3, 

 p. 26, 54, Taf. I. fig. 4, c. b. Taf. H. fig. 5, d. ; 

 Nnrdmann, Microgr. Beitr. Hft. 1, p. 79, 81, Taf. 

 VII. fig. 2, Taf. v. fig. 6 ; and Baer, Nov. Act. 

 Aciid. Leop. XIII. pt. 1, p. 665, Taf. XXXn. fig. 

 2). V^\l\i Distomum hepaticum, these ramiflca- 

 tioa? are very fully developed ; see Mehlis, Observ. 

 de Distomate, fig. 1, 2, 7, 8. In the very remark- 

 able genus Diplozoon, the digestive canal consists 

 of a single tube which traverses the whole body 

 upon the median Une, and sends ofi' laterally 

 ramified caeca, while at the point of junction of 

 the two bodies of the animal it dOates into a stom- 

 achal cavity ; see Nordmann, loc. cit. Hft. 1, 

 p. 67, Taf. V. fig. 2. The blackish ramifications 

 of Poli/stomum inte^errimum, and which have 

 been regarded by Baer (Nov. Act. Acad. Leop. 

 loc. cit. p. 6S2, Taf. XXXn. fig. 7, 8) and other 

 authors as a digestive canal, belong to the subcu- 

 taneous pigmentary net-work already mentioned. 



9 The digestive canal of Trematodes is usually 

 partly filled with blood which they have absorbed, 

 and partly with brown or yellowish chyme ; it is 

 therefore evidsnt how, from the thinness of its 

 walls, it would, when empty, entirely escape the 

 observation. 



1 Among the Nematodes, and Gordiacei, there 



10* 



are, moreover, species which have very rudiment- 

 ary digestive organs. In Sphaerularia bombi, 

 there is neither mouth nor anus, and in the plac* 

 of the intestinal canal there is a row of long sacs 

 clinging together, and aroimd which the genital or- 

 gans are coiled (fViei:mann's Arch. 1838, I. p. 

 305). In Filaria rigida, living in the intestines 

 of Aphodius JimetaTius, I have found no digest- 

 ive canal whatever (MiiUer^s Arch. 1836, p. 33). 

 In the various species of Mermis, there is a dis- 

 tinct mouth, CESophagus and intestine, but this last 

 ends in a caecum. I have been unable as yet to 

 positively determine a mouth with Gordius aqua- 

 ticus ; the anus is certainly wanting, and it might 

 be questioned if the two tubes which traverse the 

 bijdy should be regarded as an intestine ; see 

 Wiesmann''s Arch."l843, H. p. 305. 



2 With Strongylus armatus, hypostomus, den- 

 tatus, and tetracanthus, the entrance of the mouth 

 is provided with a circle of horny teeth, which are 

 moved by special muscles ; see Mehlis, Isis. 1831. 

 p. 78, Taf. n. fig. 5, 6. With Spiroptera stron- 

 gylina, I have seen the entire internal surface of 

 the mouth provided with a spiral, horny swelling. 

 In Cucullanus, there is a very complicated appa- 

 ratus for opening and closing the mouth, composed 

 of soUd, horny pieces. 



3 With Anguillula fluviatilis, Oxyuris vermi- 

 cularis, Ascaris aciiminuta, brevicaudata, dac- 

 tyluris, oxyura, and vesicularis, the cesophagns 

 has this enlargement. But it is divided into two 

 portions by a prominent constriction with Cucul- 

 lanus elegans, Physaloptera alata, Spiroptera 

 anthuris, europtera, obvelata, and crassicau- 

 da. In Trickocephalus, it is very long, and has 

 behind very many constrictions, which are succes- 

 sive at short intervals ; see Mayer, Beitr. &c. Taf. 

 I. 11. With Trichosoma falcomtm, it is equally 

 long and divided into many sections, which give it 

 an articulated aspect. 



4 By many Helminthologists this tube has been 

 called msophagut, and its dilatation stomachua. 



