38 A NATURAL HISTORY OF THE SFA.S 



attached to a crab, deriving nourishment by sending 

 an endlessly ramifying series of roots into every portion 

 of the more active crustacean's interior. A crab so visited 

 is usually doomed, but before succumbing to its repulsive 

 parasite undergoes various modifications, the male crabs 

 taking on certain female characteristics. 



The Isopods — claw-footed crustaceans — are typified in 

 the common Wood Louse, and in the maritime zone present 

 a galaxy of varied forms. They have no carapace and the 

 eyes are set flat and not raised on stalks. 



The Gribble Limnoria, though of minute proportions, 

 does immense damage to all wooden structures exposed 

 to salt water, eating away the wood until it is of the con- 

 sistency of a sponge. Many ships, piers, and harbour 

 structures have thus been completely undermined much as 

 terrestrial woodwork often succumbs to the death-watch 

 beetle. 



The Isopods also include the common Sea-Slater 

 (Ligia) — a useful scavenger — and many large and handsome 

 fish parasites, including the strange degenerate creature 

 Bopjrus. In the latter crustacean the female takes up 

 residence in the gill chamber of the common prawn, causing 

 a blister-like protrusion of the carapace and earning for 

 its host the fishermen's somewhat ribald appellation of 

 " Face-ache " Prawn. 



The Amphipods are well known to all by the Common 

 Fresh- water Shrimp and the still more abundant Sandhopper 

 or " Beach Flea." The latter literally swarms on most 

 shores, and unlike the Fresh-water Shrimp always keeps 



