Chsetopterus Variopedatiis. 505 



vertically imbedded tube does not pennit a constant current of water 

 to pass over the worm. Its pair of long slender tentacles is extended 

 from the orifice of the tube. It scrapes the surface of the diatoms 

 of the aquarium and those which are dislodged are swept up the 

 ciliary grooves to the mouth, which I have never seen above the 

 orifice of the tube. The tentacles further aid in the removal of the 

 faeces to the exterior by means of a reversal of their ciliary vibra- 

 tion. 



The perfection of the palettes, correlated with the U-shaped tube, 

 more than compensates for the shorter tentacles, which, in Chaetop- 

 terus are more primitive than in Spiochaetopterus. 



The Removal of Excreta. — The cylindrical faecal masses are dis- 

 charged into the horizontal portion of the glass U-tube where the 

 animals lie while feeding. The masses are discharged at intervals 

 of several minutes, but are not swept out of the tube as rapidly as 

 they are discharged from the intestine. They remain till a fairly 

 constant number has been discharged, then the palettes vibrate more 

 strongly and expel them to the exterior. ^Vllen the small specimens 

 upon which I have made the observation were well fed they expelled 

 from ten to twenty masses at intervals of four minutes. 



The faeces are expelled with considerable force by the current of 

 water which traverses the tube. Laffuie's statement that "the faecal 

 matters owe their density chiefly to the amount of sand in them" 

 is true only in part, as has been stated earlier. The sand grains are 

 usually rejected and expelled from the tube. My obseiwations as 

 described above refute his statement (page 310) : "The interior 

 of this tube is never soiled by the faecal matters, which, if it 

 had occurred, would accumulate in the steepest part and would 

 finally obstruct it completely." "That supports the supposition that, 

 at the moment of expulsion of the faecal matters to the exterior, the 

 inferior region of the animal which is occupied by the anus, ought 

 to be situated near the orifice of the tube, in such a manner that 

 these matters fall to the exterior." 



The Fortn and Size of the Tubes. — The parchment-like tubes usua- 

 ally have the form of a broad U, which is thick-walled and wrinkled 

 in old tubes, but thin and flabby in those recently formed. The 



