$ 108. THE HELMINTHES. 118 
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 esophagus, which is 
usually dilated claviform at its lower extremity. When the cesophagus is 
very long, it has one or more constrictions. 
of three longitudinal muscles which are united by longitudinal seams. 
It is nearly always composed 
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 fluviatilis, and Lucioperca. 
7 See Miram, Owen, and Diesing, 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. 
8 In many sp allied to Mon trigo 
nocephalum, the two intestinal tubes have simple 
caeca upon both sides of their entire length. In 
Octobothrium lanceolatum, the structure is the 
same; see Mayer, Beitr. p. 21, Taf. ITI. fig. 3. 
These lateral caeca are more or less ramified in Oc- 
tobothrium palmatum, sagittatum, Merlangi, 
Polystomunt appendiculatum, and Tristomum 
elongatum (Leuckart, Zool. Bruchstiicke, Hft. 3, 
p. 26, 64, Taf. I. fig. 4, c. b. Taf. U1. fig. 5, d. 5 
Nordmann, Microgr. Beitr. Hft. 1, p. 79, 81, Taf. 
VII. fig. 2, Taf. V. fig. 6; and Baer, Nov. Act. 
Acad. Leop. XIII. pt. 1, p. 665, Taf. XXXII. fig. 
2). With Distomum hepaticum, these ramifica- 
tions are very fully developed ; see Mehdis, 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 line, and sends off laterally 
ramified caeca, while at the point of junction of 
the two bodies of the animal it dilates into a stom- 
achal cavity; see Nordmann, loc. cit. Tift. 1, 
p. 67, Taf. V. fig. 2. The blackish ramifications 
of Polystomum integerrimum, and which have 
been regarded by Baer (Nov. Act. Acad. Leop. 
loc. cit. p. 682, Taf. XXXII. fig. 7, 8) and other 
authors as a digestive canal, belong to the subcu- 
taneous pigmentary net-Wwork already mentioned. 
9 The digestive canal of Trematudes is usually 
partly filled with blood which they have absorbed, 
and partly with brown or yellowish chyme ; it is 
therefore evident 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 place 
of the intestinal canal there is a row of long sacs. 
clinging together, and around which the genital or- 
gans are coiled (Wiegmann’s Arch. 1838, I. p. 
305). In Filaria rigida, living in the intestines 
of Aphodius fimetarius, I have found no digest~ 
ive canal whatever (Miiller’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 acaecum. 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 
body should be regarded as an intestine; see 
Wiegmann’s Arch. 1848, II. 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 Mehiis, Isis. 1831, 
p. 78, Taf. II. 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 svlid, horny pieces. 
3 With Anguillula fluviatilis, Oxyuris vermi- 
cularis, Ascaris inata, brevicaudata, dac- 
tyluris, oxyura, and vesicularis, the cesophagus 
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 Trichocephalus, it is very long, and has 
behind very many constrictions, which are succes- 
slve at short intervals ; see Mayer, Beitr. &c. Taf. 
I. Ul. With Trichosoma falconum, it is equally 
long and divided into many sections, which give it 
an articulated aspect. 
4 By many Helminthologists this tube has beem 
called esophagus, and its dilatation stomachus- 
