HYDRACTINIA ECHINATA. 43 



upon small creatures such as Infusoria, which 

 may be attracted thereto. The possible 

 benefit derived by the crab may be found in 

 the protection afforded against enemies (Fish, 

 etc.), by reason of the poison darts of the 

 polypites, but the polypites reap the main 

 advantage, since they are, almost without 

 exception, found associated with the crab, 

 whereas the latter is more often found 

 not accompanied by them. 



This is a particularly interesting species, 

 and the horny skeleton should be examined 

 with a microscope, in connection with that 

 of Coppinia arcta, Antennularia ramosa, and 

 several other species. 



H. echinata is common along our shores 

 in warm weather, but the crab with its 

 commensal retires to deeper water when the 

 temperature is low. 



When thickly covered with gonophores, 

 the whole colony is a pink colour, and very 

 noticeable. 



