134 



THE TURBELLARIA. 



<^12^, 



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

 staiF-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 nuiscles 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 MicTostomum lineare, Örstrd, these 

 prehensile organs so closely resemble those of 

 Hydra that they need not be described. According 

 to Örsled they are urn-shaped glands in the centre 

 of which are parabolic bodies which are constantly 

 in motion (loc. cit. p. 73^ Taf. II. fig. 18). But 

 liad he pressed these organs between two iilates of 

 glass, he would have seen the protruding filament, 

 together with its double hooks. 



'■i 1 have seen these corpuscles protruding through 

 the lateral border of the body of Planaria lactea. 

 In the dorsal papillae of Thysanozoon Diesingii., 

 a part of tliese corpuscles are contained in cells ; 

 but the others are free and often protrude through 

 the skin. With Mesostonium Ehrenbergii, and 

 rostratum, they are arranged in rows in the 

 anterior half of the body, forming striae, which 

 quickly catch the attention. Ör.ited has taken 

 these corpuscles for as many muscular columns 

 (loc. cit. p. 70, Taf. II. fig. 26, 37). The spines 

 which, according to him (loc. cit. p. 72, Taf. II. fig. 

 29, 3-1) cover the eutii-e surface of Macrosto?num 



hystrix, are probably of the same nature, as may 

 also be said of the delicate short bristles found 

 everywhere under the skin of Derostomum leu- 

 cops, Dug:es. 



Quatrefages, in his monograph on marine 

 Planariae (Ann. d. Sc. Nat. IV. 1845, p. 146, PI. 

 VIII. fig. 9, 10), also mentions various formations 

 wliich, partly as spines, partly as nettling or- 

 gans, are found in the skin of certain Dendrocoeli. 



1 The mode of locomotion by which these animals 

 move over solid bodies, or upon the surface of the 

 water, has not yet been satisfactorily explained. 

 The ciliated epithelium cannot here be the principal 

 agent. According to Schulze, loc. cit. p. 32, the 

 staff-like corpuscles projecting from the back of 

 these animals, and which he terms bristles, are used 

 as oars. 



According to Mertens (Mira, de I'Acad. de St. 

 Petersbourg, 6^""^, sir. II. 1833, p. 5), Planaria 

 lichenoides moves by means of the protruded 

 lobes of its pharyngx. 



2 Tor example, Mesostomum. 



