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expanded the first pair of setigerous segments and split the tube longitudi- 

 nally at its outer side, then withdrew quickly into the deeper portion of the 

 tube. Fifteen or twenty seconds later the worm reappeared at the level of 

 the sand, extended the rent a little higher and withdrew. This action was 

 repeated five times in extending the rent, seven millimeters, to the end of 

 the tube. The rent was produced by means of the expansion of the mus- 

 cular setigerous region and not by the sharp lance-shaped setae as one 

 might suppose. The rent occurred in a position opposite the ventral sur- 

 face of the body. When the tube was split to its extremity the worm 

 thrust one side of the anterior region through the cleft and removed the 

 sand about it by means of its setigerous notopodia. They pressed a portion 

 of the sand aside but some was removed backwards into the tube and later 

 discharged at the other end. 



When the tube was split to its end the worm spread the basal portion 

 of the rent by a slight expansion of the ventral side of its lower lip and 

 the foremost i)ortion of the anterior region. The worm remained in this 

 position for fifteen or twenty seconds then withdrew into its tube for a 

 half minute, alter which it took a position a little nearer to the orifice of 

 the tube. The performance was repeated till the edges were reunited by a 

 wedge-shaped insertion of parchment that widened to three millimeters 

 just below the level of the sand. I could not determine which region of 

 the body was most active in the secretion of the mucus, which becomes 

 parchment-like, but I observed that it was shaped by the lower lip of the 

 buccal funnel, and that the parchment film had advanced a little higher 

 each time the animal applied its ventral lip to the cleft. The splitting of 

 the tube and the closure of the rent were completed in thirty-five minutes. 



The splittings occur indifferently on any portion of the circumference 

 of the tube, but they are found chiefiy on the upper side of the horizontal 

 portion. When they are extensive it is indicated by the abundance of sand 

 discharged at long intervals from one arm of the tube. I have found some 

 large tubes that had strips of thin parchment two centimeters wide and 

 as long as the horizontal portion of the tube. 



The new portion of the wall is thin and membranous at first and, while 

 it becomes thicker with age, can be observed, long after its formation, as a 

 strip somewhat thinner than the remaining portions of the wall. Its 

 inner surface is smooth, like the inner wall of the other portion, and its 

 outer surface is similarly covered with sand. The wide, horizontal portion 

 of nearly e^-ery tube bears one or more of these strips inserted between the 



