FUNCTION OF THE TENTACLES. 73 



flattened, tubular filaments, furnished with strong mus- 

 cular parietes. Each of these hollow band-like ten- 

 tacles may be rolled longitudinally into a cylindrical 

 form, so as to enclose a semicircular space, if they only 

 imperfectly meet. This inimitable mechanism enables 

 each filament to take up and firmly grasp, at any point 

 of its length, a molecule of sand, or, if placed in a 

 linear series, a row of molecules. But so perfect is 

 the disposition of the muscular fibres at the extreme 

 end of each filament, that it is gifted with the twofold 

 power of acting on the sucking and on the muscular 

 principle. In addition to the two important uses 

 already assigned to these tentacles, they constitute also 

 the real agents of locomotion. They are first out- 

 stretched by the forcible ejection into them of the 

 peritoneal fluid, they are then fixed like so many 

 slender cables to a distant surface ; and then, shorten- 

 ing in their lengths, they haid forward the helpless 

 carcass of the worm." * The carcass of the worm is 

 by no means so helpless as here described. It is true 

 that the tentacles are employed to drag the animal 

 along. You observe how that one is crawling up the 

 sides of the glass, and now hangs suspended to the 

 floating weed : but you may also observe him wrig- 

 gling about his body with great activity, and by these 

 contractions he is enabled to make progress, even when 

 deprived of his tentacles. 



There is a more serious objection, however, to 

 be made to the passage I have just abridged. Dr 



* Williams : Report, p. 194. 



