134 
of the arms of Polyps. 
THE TURBELLABIA. 
§ 122. 
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 Rhabdocoéli, the parenchymal muscles 
may be made out; and in the larger Planariae, when the muscles are visi- 
ble, their fibres appear unstriated. 
The small Rhabdocoéli swim by means of their ciliated epithelium, like 
many Infusoria, their bodies revolving on its longitudinal axis; while the 
flattened Dendrocoéli 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 
prehensile organs so closely resemble those of 
Hydra that they need not be described. According 
to Orsted 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 
had he pressed these organs between two plates of 
glass, he would have seen the protruding filament, 
together with its double hooks. 
2 Ihave seen these corpuscles protruding through 
the lateral border of the body of Planaria lactea. 
In the dorsal papillae of Thysanozoon Diesingii, 
® part of these corpuscles are contained in cells ; 
but the others are free and often protrude through 
the skin. With Mesostomum Ehrenbergii, and 
rostratum, they are arranged in’ rows in the 
anterior half of the body, forming striae, which 
quickly catch the attention. Orsted has taken 
these corpuscles for as many muscular columns 
(oc. cit. p. 70, Taf. II. fig. 26,37). The spines 
which, according to him (loc. cit. p. 72, Taf. II. fig. 
29, 34) cover the entire surface of Macrostomum 
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, Duges. : 
Quatrefages, in his monograph on marine 
Planariae (Ann. d. 8c. Nat. IV. 1845, p. 146, Pl. 
VIII. fig. 9, 10), also ions various formati 
which, partly as spines, partly as nettling or- 
gans, are found in the skin of certain Dendrocoéli. 
1 The mode of locomotion by which these animals 
move over solid bodies, or upun the surface of the 
water, has not yet been satisfactorily explained. 
The ciliated epithelium cannot here be the principal 
agent. According to Schudze, 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 (Mém. de I’Acad. de St. 
Petersbourg, 6eme, sér, II. 1833, p. 5), Planaria 
lichenoides moves-by means of the protruded 
lobes of its pharyngx. 
2 For example, Mesostomum. 
