SEA-WORMS. 189 



comb of gills displayed by the Sahellce and Serpulce, only puts 

 forth a truncated head adorned by a great number of long 

 thread-like tentacles. These tentacles, wandering far and 

 wide, adhere to little specks of sand and bits of shell, which 

 they bring together and cement in a circular wall, so as to 

 form their tube. This gravelly dwelling is not made, hke 

 some tubes, by the mere fortuitous rolling together of par- 

 ticles in the glairy secretion surrounding the body of the 

 animal ; but regularly and systematically laid on, fragment 

 by fragment, to the edge of the structure. At the larger 

 end of the tube may be observed a number of very thin 

 branching tubes, formed of more minute grains of sand. 

 These are sheaths, ^Yith which the working tentacula have 

 temporarily clothed themselves, and from which they have 

 withdrawn. 



Specimens in captivity were observed by Mr. Gosse to 

 abandon their tubes and crawl about the glass jar by means 

 of their tentacles, which adhered to its sides. They also 

 creep, body downwards, on the surface of the water in the 

 same manner that Water Snails do. Individuals may be seen 

 at the present time (or might have been a week or two since) 

 working away in the construction of then- brittle habita- 

 tions, both at Mr. Lloyd^s estabHshment and at the Park 

 Gardens. 



