134 THE TURBELLARIA. § 122. 



of the arms of Polyps/'^ These bodies contain six or eight, or even more, 

 staff-like, colorless corpuscles,, which are parallelly arranged side by side, 

 or curved a little spirally. With their further development, the envelope 

 disappears, and they then remain free under the skin, but sometimes pro- 

 jecting through it.*^' 



CHAPTER II, 



MUSCULAR SYSTEM AND LOCOMOTIVE ORGANS. 



§ 122. 



Although their parenchyma is extremely contractile, yet the Turbellaria 

 have only a very feebly -developed muscular system. 



In many small species of the Rhabdocoeli, the parenchymal muscles 

 may be made out ; and in the larger Planariae, when the muscles are visi- 

 ble, their fibres appear unstriated. 



The small Rhabdocoeli swim by means of their ciliated epithelium, like 

 many Infusoria, their bodies revolving on its longitudinal axis ; while the 

 flattened Dendrocoeli crawl along like the Gasteropoda.*^* Many larger 

 species of the first order,*^^ appear to float from place to place by means of 

 their epithelium, thus really neither creeping nor swimming. 



1 With Microstomum lineare, Orsted, these hi/strix, are probably of the same nature, as may 

 prehensile organs so closely resemble those of also be said of the delicate short bristles found 

 Hydra that they need not be described. According everywhere under the skin of Derostomum len- 

 to Orsted they are urn-shaped glands in the centre cops, Duges. 



of which are parabolic bodies which are constantly QuntrefageSi in his monograph on marine 



in motion (loc. cit. p. 73, Taf. II. fig. 18). But Planariae (Ann. d. Sc. Nat. IV. 1845, p. 146, PI. 



had he pressed these organs between two plates of VIII. fig. 9, 10), also mentions various formations 



glass, he would have seen the protruding filament, which, partly as spines, partly as nettling or- 



together with its double hooks. gans, are found in the skin of certain Dendrocoeli. 



2 I have seen these corpuscles protruding through 1 Tlie mode of locomotion by which these animals 

 the lateral border of the body of Planaria lac tea. move over solid bodies, or upon the surface of the 

 In the dorsal papiUae of Thysanozoon Diesingii, water, has not yet been satisfactorily explained. 

 a part of these corpuscles are contained in cells ; The ciliated epithelium cannot here be the principal 

 but the others are free and often protrude through agent. According to Schulze, loc. cit. p. 32, the 

 the skin. With Mesostomum Ehrenbergii, and staff-like corpuscles projecting from the back of 

 Tostratum, they are arranged in rows in the these animals, and which he terms bristles, are used 

 anterior half of the body, forming striae, which as oars. 



quickly catch the attention. Orsted has taken According to Mertens (Mim. de I'Acad. de St. 



these corpuscles for as many muscular cokunns Petersbourg, 6^"", s^r. II. 1833, p. 5), Planaria 



(loc. cit. p. TO, Taf. II. fig. 26, 37). The spines lichenoides moves by means of the protruded 



which, according to him (loc. cit. p. 72, Taf. II. fig. lobes of its pharyngx. 



29, 34) cover the entire surface of Macrostomum 2 For example, Mesostomum. 



