POLYCHiETA OF THE L.M.B.C. DISTRICT. 145 



In one case, an individual had seized upon a shore blown 

 beech leaf, constructing on its surface a mucus tunnel in 

 which it lay hid — very similar in appearance to the cocoons 

 of many insects. A species of pycnogonid is frequently 

 found parasitic (?) clinging to the outside of these mucus 

 tubes. 



Nereis (Nereilepas) fucata, (Savigny). 



Hab : 4, 8, 10, 11, S, M, Mp. 



The Nereis hilineata of Carrington. It is frequently 

 met with in dead Fnsus and whelk shells. Also in 

 about 90^/o of such shells w4iich have been taken 

 possession of by Hermit-crabs {Pag urns). If a shell 

 containing one of these strangely assorted couples be 

 watched in an aquarium, the forepart of the worm's body 

 will be seen to emerge slowly from the interior depths 

 and sway gently from side to side, above the back of the 

 crab, surveying keenly the environment. The fellow- 

 lodgers together dwell in amity, though what the mutual 

 relationship existing between the tw^o is I have never seen 

 explained. My own opinion — seeing how often the w^orms 

 occupy otherwise uninhabited shells — is that Nereis fucata 

 is the first tenant and that it tolerates the intrusion of the 

 Hermit-crab chiefly because it can easily steal morsels of 

 the plentiful supply of food w^iich the latter can generally 

 manage to procure. Besides the Pagurus furnishes means 

 of locomotion unattended with danger, and his presence in 

 the mouth of the shell prevents other intruders who might 

 be unwelcome from getting entrance. The Hermit-crab 

 on the other hand, I believe, derives no benefit from the 

 partnership and takes no notice of the worm as long ex- 

 perience has taught him that he cannot dislodge the 

 latter, who occupies the coign of vantage, possesses 

 superior agility and a pair of stout mandibles. Indeed 

 the worm can easily turn the Hermit out if so disposed, 



