TUBE-MASONS. 317 



the closing of the opening is generally prevented by 

 a corresponding growth of the tube. In several 

 specimens examined the extremity of the tube had 

 grown in a direction at right angles to the upper 

 surface of the coral, and projects a full half inch 

 above that plane. The coral, however, has formed 

 along the sides of this projection, and has covered it 

 to the very apex. The result is the formation of 

 variations in the regular growth of the coral, which 

 may be likened to coral gall, such as is formed by 

 certain crustaceans. The greater part of the worm- 

 tube lies in sight, on the under side of the coral, 

 while its terminal opening is almost wholly con- 

 cealed, being surrounded by the live coral com- 

 munity, through which there is, however, a small 

 opening into the tube cavity, inhabited by the 

 worm." l The modifications of the growing coral 

 structure always commence in the vicinity of the 

 opening of the worm-tube. As the growth of the 

 coral proceeds, that portion which lies on the edge of 

 the saucer-like disk surrounds the obstruction, and, 

 when this takes place, the end of the worm-tube 

 grows upward, and seems to rise out of the midst of 

 the growing coral. 



Other kinds of coral, belonging to other genera, 



1 "Annelid Messmates with a Coral," by I. W. Fewkes, in 

 American Naturalist^ vol. xvii. 1883, p. 595. 



