24 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



tube placed in a well lighted part of the tank. For some days 

 after this the posterior end of the worm could be seen moving 

 slowly up and down the extension, and, ere long, several new 

 pebbles were added to the extremity. Movement of the whole 

 tube in the direction of the proximal end was again noticed, 

 and this is still (October 18th) going on, though the daily rate 

 of movement is slower. At the same time the worm has been 

 adding to the open end of the tube, 8 millimetres of normal 

 construction having been added in 21 days. It is worthy of 

 note that since its removal to its present position the worm 

 has not been seen expanded in the daytime, so that the addition 

 to the open end of the tube must be carried on during the 

 night. A little heap of excreta which lies immediately below 

 the aperture of the tube tends to confirm this supposition. 



"Before leaving the subject of tube-building Polychaetes, 

 it may be mentioned that Serpula vermicular is, Potamilla 

 reniformis and P. torelli have appeared spontaneously and 

 are now well established in several of the table tanks in the 

 Aquarium. The latter species of Potamilla has not been 

 previously recorded from the L.M.B.C. District. 



<k Early in May a large number of specimens of the brittle- 

 star Ophiocoma nigra were found in a crab-pot which had 

 just been brought in from the fishing grounds. Fifty of the 

 largest were selected and placed in one of the table tanks, 

 where they are still in vigorous health. The rapidity with 

 which this brittle-star detects the presence of food is remark- 

 able. A small bit of fish or mussel dropped into the tank 

 attracts the attention of half the number of specimens in a 

 few seconds, as shown by an almost simultaneous move towards 

 it from different points. On one occasion the following experi- 

 ment was made. At 10.15 a.m. a small piece of mussel was 

 suspended by means of a thread about f inch below the surface 

 of the water. Its presence was detected by a number of the 

 brittle-stars in 15 seconds. At 10.20 a.m. some of them had 



