MARINE BIOLOGICAL STATION AT PORT ERIN. 23 



more favourable for observation. The proximal end of the 

 tube, however, had been imperceptibly worked by the worm 

 beneath the small gravel which covers the bottom of the tank. 

 A number of tiny pebbles had been cemented to the tube, 

 and the tube itself cemented at a number of points to the 

 bottom of the tank. On discovering this the Curator decided 

 not to disturb the worm further. The distal, open end of the 

 tube was now supported on the stone, in order to keep it out 

 of the reach of neighbouring anemones, and still closer watch 

 was kept upon the behaviour of the worm. Shortly afterwards 

 it became evident that the worm was moving its tube bodily 

 in the direction of its proximal end. A dark ring around the 

 tube afforded a fixed point, by noting the position of which 

 in relation to certain recognisable pebbles which lay near it 

 the Curator was able to ascertain that the rate of movement 

 was about 1 millimetre per 24 hours. At this rate the tube 

 was moved at least 2 centimetres. Later on a slight elevation of 

 the surface of the gravel was noticed beyond the point where 

 the proximal end of the tube was known to be originally. 

 Careful removal of the gravel by means of a large camel-hair 

 pencil revealed an interesting state of affairs. The worm had 

 made a considerable extension of its tube, consisting of the 

 chitin with which the tube of Sabella is normally lined, and 

 instead of mud the surrounding pebbles had been used to 

 cover it. The tube was now carefully removed, and in doing 

 this the Curator noticed that the extension was attached at 

 many points by chitinous threads to the bottom of the tank. 

 Measurements of the tube showed that its total length was 

 55*5 centimetres, 29*5 centimetres of which consisted of the 

 original mud-invested tube, and 26 centimetres of the chitinous 

 extension of the proximal end. Beginning at the point where 

 the former condition merged into the latter, the pebbles were 

 removed from 5 centimetres of the extension, a short length 

 of glass tubing- was slipped over the exposed portion and the 



