50G- Howard Edwin Enders. 



horizontal portion of the U is wider than the conical vertical arms 

 that protrude a few' centimeters above the substratum. The simple 

 U-form is often modified in tubes that occur in shoals of sand and 

 shells. The arms may here be so constructed that they turn abruptly 

 aside from large shells that may be in their way. Tubes are fre- 

 quently found with three arms protruding above the sand. These 

 are tubes that have been enlarged by the extension of the horizontal 

 portion and the formation of a new arm (Fig. 2). A septum at the 

 base of the intermediate arm separates its cavity from that of the 

 horizontal j)ortion. I have found intermediate arms with little or 

 no sand, some completely filled, while many have begun to macerate. 

 Every large tube bears the shreds of one or more of these macerated 

 intermediate arms, or the crescentic scars that mark their former 

 luiion with the newly formed extension. The annulations near the 

 orifices and the longitudinal strips of thinner, sand-covered, parch- 

 ment alternating with thicker portions of the tubes will be taken up 

 and described in the chapter dealing with the formation of the 

 tubes. 



There is great diversity in the size of the tubes. A very young 

 worm formed a characteristic U-shaped tube three millimeters in 

 diameter at its widest portions, and one and three-fourth milli- 

 meters at its orifices. The distance between the orifices measured 

 fourteen and one-half millimeters, and the length of the arms 

 (measured from the low^er side of the horizontal portion as the base) 

 was sixteen millimeters. During their breeding season I have col- 

 lected specimens which ranged in length (between the orifices) 

 from six to fifty centimeters, and with arms six to twenty-tw'O 

 centimeters long (vertically). 



Size of Specimens Taken from the Tube. — The size of tubes, Avhile 

 it increases considerably with the age of the individuals, can be 

 regarded only as a general index of the size of the annelid which it 

 encloses. .One individual which was less than two centimeters 

 long, consisted of fifteen seginents in the posterior region. It occu- 

 pied a tube that measured three centimeters between its orifices. 

 Another specimen, which had eighteen sexual segments, was found 

 in a flabby tube that was three and one-half centimeters long; this 



