HABITS OF THE OtftJPHlDJE. 313 



It is possible that in making the attachments small 

 grains of sand may be affixed on either side of the mem- 

 branous tube, thus forming the first side-walls, though 

 perhaps these may be filled in a little later. (Such 

 advanced walls exist in several of my specimens). This 

 done, the worm will make practical use of its shelter by 

 turning the tube over, so that the little shell shall over- 

 hang the mouth of the tube. So protected, the worm will 

 travel along until it finds another suitable flat fragment, 

 which in its turn is firmly attached to the membranous 

 tube (and side walls) on the opposite side to the first, and 

 in such a position as to extend in advance. The wall-build- 

 ing and tube-turning processes are then repeated, and this 

 worm searches around for a third shell. The edge of this, 

 when found, is brought into contact with the front edge 

 of the first shell (now once more on the sea-bottom), and 

 it is. so cemented and affixed to the tube, which thus grows, 

 the process being repeated to any extent, the internal 

 lining and protective valves being also formed accordingly. 

 Though the foregoing is to some extent an imaginary 

 sketch, it is partially confirmed b}^ observation of the pro- 

 cess adopted by the worm when its tube becomes incon- 

 veniently long and heavy. In such an event a portion 

 will be detached. A specimen from Plymouth, the tube 

 of which was about 3 inches long, and consisted chiefly of 

 fiat pieces of stone, while in my aquarium found this too 

 great a load to pull about, and one evening, when I was 

 watching, separated a portion an inch long 1 . The stones 

 were loosened from each other by the jaws, or some other 

 means, invisible, owing to the operation taking place inside 

 the tube. The result, was, of course, a fracture, leaving 

 the tube terminated by a flat stone, upon which were left 

 the two little sandy side walls ; the end of the inner tube 

 was cut, and for the moment unprotected. 



