136 



THE TURBELLARIA. 



§125. 



CHAPTER V. 



DIGESTIVE APPARATUS. 



§125. 



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

 diiferent types. But in both orders, the location of the mouth varies so much, 

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

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

 that also. '^'' ■■-ills of the intestinal canal are always intimately blended 

 with the ])a. . iP the body. 



With the llhabc, il, 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 -""ecum to the anterior portion of the body.^' With 

 the Dendrocoeli the muuth 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 

 ientaculata, and Eurylcpta cornuta, and upon 

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

 port a part of the eye dots. 



1 The mciutlL ;iiiil cylindrical oesophagus of Gy- 

 ratrix henniiji/iroilitiia, and Vortex truncata,a.ve 

 at the ceplialic extremity {Ehrenberg, Abhandl. 

 <1. Berl. Aliad. 1835, p. 178, Taf. I. fig. 2, 3). But 

 the mouth and annular oesophagus of Derosto- 

 mum is situated just back of this extremity, into 

 which, however, the coecal intestine extends. The 

 «esophagus is also annular with Mesostomvm, 

 and 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 

 <;oecally far into the anterior extremity (Orsted, 

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

 'laf. 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 (ßaer, loc. cit. p. 



* [ § 125, note 2.] With Phagocata {Planaria) 

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

 1848, p. 248) foimd, insteiwl of a single sucker, 

 twenty-three,ln the full-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. — Ed. 



716, Tab. XXXIII. fig. 8-11, and Duges, loc. cit. 

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



The large and plicated oesophag\is of Planaria 

 tremeltaris, constitutes the transition to the ten- 

 tacular form of the deglutitory organs (Dugis, loc. 

 cit. XV. PI. IV. fig. 20, 21). Fully ramift.'d ten- 

 tacles are found with Planocera sargas.sicola, 

 pefliirida, 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, 1836, 

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

 many DendrocoCli has been figured by Baer, Du- 

 gis, and Hertens, 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 lesophagus 

 and intestine of Mesostomum Ehrenbergii ; hut 

 he himself admits that this view is not yet well 

 founded.! 



t [ § 125, note 3.] Will (Müller'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 (Dendrococlum lac- 

 teuin, Planaria torva, and nij^ra). — Ed. 



