131 



and diatoms on the bottom conlorni to the U-habit, though iu a horizontal 

 plane, with one side of the tube cemented to the floor of the vessel. 



The linear extensions of the tubes are formed at such intervals as the 

 rapid gi-owth of the worm requires. 'I he length of the tubes, and the 

 dates on which the enlargements were completed by two worms which 

 I reared from larvae taken in the tow-net are as follows:* 



Early in September of 1905 I collected three worms whose tubes 

 averaged fifty-one millimeters between the orifices and five whose recently 

 discarded intermediate arms were sixty millimeters from the ends with 

 which they formed the smaller U-shaped tubes. The horizontal extensions 

 increased their length to fifteen centimeters iu the smallest and twenty-two 

 and one-half in the longest specimen. Many thick-walled tubes are found 

 with scars of intermediate arms which indicate that they were increased 

 from about this size to about forty centimeters. The longest tubes show 

 that they were increased, by a linear extension of ten centimeters, to fifty 

 centimeters. 



The tubes also undergo an enlargement in diameter as the animal grows 

 in thickness. This splitting and enlargement of one of its arms I observed 

 in specimen No. 4 during one night in September of 1905. The worm pushed 

 the rim of the buccal funnel nearly to the margin of the orifice, and slowly 

 moved the ends of the tentacles over the rim of the tube. (In order to 

 enter this narrow portion of the tube from below the edges of the buccal 

 funnel and anterior region of the body was curved dorsalwards and con- 

 siderably contracted till they become conical in form.) The animal re- 

 mained iu this position in the tube about five seconds then slowly with- 

 drew into the deeper portion. This was repeated in thirty seconds but this 

 time it withdrew only to the level of the sand. Here the worm suddenly 



*Both worms enlarged their tubes to 76 and 71 millimeters, respectively, between 

 September i2th. when they were brousht to the Biological Laboratory of the Johns Hop- 

 kins University, and my return, October 4. 1905. The worm in No. 4 had extended its 

 tube to the glass wall of the aquai-ium on May 8-9, 1906. The U-shaped tube now meas- 

 ured 85 millimeters between the orifices. 



