344 FUNCTIONS AND INSTINCTS. 



face, looking like a little worm creeping upon 

 them ; 1 and forming convolutions ; I have a 

 specimen on a valve of the cock's-crest oyster, 2 

 which is bound down by a process issuing ap- 

 parently from the disk of the oyster-shell itself, 

 how produced and thrown over the Serpula it 

 seems not easy to conjecture. Different species 

 of these worm-shells are often found, embracing 

 each other with their convolutions, on the same 

 shell ; wherever the sea is or has been, they 

 abound either in a recent or fossil state ; they 

 are found on rocks, and sea- weed as well as on 

 marine shells, and those of lobsters. The Serpu- 

 lidans, in general, imitate the spiral structure 

 of the Trachelipod and other Molluscans, as is 

 particularly evident in Siliquaria and Vermetus, if 

 indeed the last genus is not itself a Molluscan, 

 as Lamarck makes it. 



Other species of this Order are taught to estab- 

 lish themselves in fissures of rocks, which serve 

 them instead of a shell to protect the membranous 

 tubes into which they retract their petaliform 

 tentacles, which together represent a beautiful 

 radiated blossom, or the nectarium of a passion- 



1 S. Triguetra. 



2 Ostrea Crista-galli. Since the above was written, in the 

 collection of the late Peter Collinson, I have seen two specimens 

 of this oyster, which had produced from the back of their shell 

 a double series of processes, with which, as with so many fingers, 

 they had taken firm hold of a piece of stick. 



