136 



THE TURBELLARIA. 



§125. 



CHAPTER V. 



DIGESTIVE APPARATUS. 



§ 125. 



With the two orders of Turbellaria, this apparatus is formed upon very 

 different types. But in both orders, the location of the mouth varies so mucli, 

 that it serves as the basis of genera, according as it is at the anterior extrem- 

 ity, or a i/Ue behind it, — or, at the middle of the belly, or a little behind 

 that also. The walls of the intestinal canal are always intimately blended 

 with the parenchyma of the body. 



With the llhabdocoeli, the mouth leads to a muscular oesophagus, which 

 is either an annular sphincter, or a longer or shorter tube, but which, in no 

 case, can be everted from the mouth. The intestinal canal is a simple cae- 

 cum extending from the oesophagus to the posterior extremity ; but with 

 those species which have the mouth situated more or less posteriorly, it 

 stretches forward as a coecum to the anterior portion of the body."* With 

 the Dendrocoeli the mouth opens into a large throat, containing a protrac- 

 tile and very movable deglutitory organ [Pharynx). 



This organ, which can be protruded entirely out of the throat while the 

 animal is eating, is either a tube composed of longitudinal and transverse 

 muscles, or a collection of lobular and ramified tentacles circularly ar- 

 ranged about the mouth. 



Its base is prolonged into the proper intestine, whose dendritic ramifi- 

 cations extend over the whole body.® 



Scarcely a trace of salivary or hepatic organs have here been found 

 with these animals. ^"* 



ages on the anterior part of the body of Planaria 

 tentaculata, and Eurylepta cornuta, and upon 

 the neck of Planocera. With the last, they sup- 

 port a part of the eye dots. 



1 The mouth and cylindrical oesophagus of Gy- 

 ratrix hertnaphroditus, and Cortex tru,ncata,ave 

 at the cephalic extremity {Ehrenberg, Abhandl. 

 d. Bcrl. Akad. 1835, p. 178, Taf. I. fig. 2, 3). But 

 the mouth and annular oesophagus of Derosto- 

 vium is situated just back of this extremity, into 

 which, however, the coecal intestine extends. The 

 oesophagus is also annular with Mesostomum, 

 aiid Typhloplana. In the first, the mouth is at the 

 middle of the ventral surface ; and in the last, a 

 little behind this point, while the intestine projects 

 coecally far into the anterior extremity (flrsted, 

 loc. cit. Taf. n. fig. 26, 31, and Focke, loc. cit. 

 Taf. XVII.). 



- The genus Planaria has become famous for its 

 movable organ of deglutition, which, being sepa- 

 rated from the body, still continues for a while to 

 swallow all presented to its mouth (Baer, loc. cit. p. 



* [ § 125, note 2.] With Pha^ocata (Planaria) 

 gracilis, Leidy (Proceed. Acad. Nat. Sc. Phil. III. 

 1848, p. 248) found, instead of a single sucker, 

 twenty-three, In the fuU-grown animal. These are 

 all protruded when the animal feeds, but when 

 not in use, are closely packed together within the 

 animal. They all connect separately with portions 

 of the dendritic alimentary cavity. — Eu. 



716, Tab. XXXin. fig. 8-11, and Dugis, loc. cit. 

 XV. p. 152, PI. IV. fig. 18, 19). 



The large and plicated oesophagus of Planaria 

 tremellaris, constitutes the transition to the ten- 

 tacular form of the deglutitory organs (Dugis, loc. 

 cit. XV. PI. IV. fig. 20, 21). Fully ramified ten- 

 tacles are found with Planocera sargassicola, 

 pellucida, and Leptoplana lichenoides. When 

 collected in the throat, they present exactly the as- 

 pect of a ramified intestine (Mertens, loc. cit. Taf. 

 I. fig. 2, 3, 6, Taf. II. fig. 3, 4, and the Isis, 18.36, 

 Taf. IX. fig. 3, b. 3, c). The ramified intestine of 

 many Dendrocogli has been figured by Baer, Du- 

 gis, and Mertens, in their works already cited.* 



3 Focke (loc. cit. p. 196, Taf. XVII. fig. 11, c. 

 f.) is inclined to regard as salivary and hepatic or- 

 gans, two large lateral vessels, and a glandular or- 

 gan which he has discovered near the oesophagus 

 and intestine of Mesostomum Ehrenbergii ; but 

 he himself admits that this view is not yet well 

 founded.! 



t [ § 125, note 3.] mil (Mailer's Arch. 1848, 

 p. 508) has shown that the brownish layer covering 

 the whole extent of the intestine of Planaria is 

 composed of hepatic glands (Dendrocoelum lac- 

 teum, Planaria torva, and nigra). — Ed. 



