560 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



them. There is no doubt M. T. Thompson is right in 

 thinking that the diatoms and foraminifera which are 

 found in the alimentary canal come from this source. 



Commensals. 

 Although E. bernhardus does not exhibit such apt 

 illustrations of commensalism as some of its allies, it 

 usually contrives to entertain some stranger in its abode. 

 To the human observer, however, it has seemed less 

 happy in its bargains than they. The Polychaet worm 

 Nereis (Nereilepas) fucata is found in many shells. 

 J. Hornell* states that 90 per cent, of the shells which 

 have been taken possession of by hermit crabs contain 

 the worm, but my records — made from the examination 

 of a large amount of material — show that in not 30 per 

 cent, were these animals found associated. The 

 frequency of this case of commensalism on the South 

 Coast is evinced by Gosse's observation that the fisher- 

 men of Weymouth are accustomed to break open the 

 hermit crab's shells for the sake of the worm inside. 



The Nereis usually remains out of sight in the back 

 whorls of the shell, but it appears at meal times, 

 thrusting its head out between the crab's foot- jaws to 

 appropriate the very morsel on which its host is engaged. 

 In several young crabs' shells (Littorina and Natica) I 

 found young N. fucata, about half an inch in length. 

 It would seem, therefore, that the worm changes house 

 with its host as both grow up. It is difficult to suggest 

 any advantage that the hermit crab can gain from the 

 presence of this guest. 



E. bernhardus is also found associated, but not in 

 the L.M.B.C. district, with the sea-anemone Sagartia 

 parasitica. It carries the coelenterate turretwise on top 

 * Fauna of Liverpool Bay, Rep. III. L.M.B.C. 1892, p. 126. 



