CRUSTACEA OF THE SEASHORE 97 



sea-weeds, when placed in an aquarium among 

 sponges, picked off the weeds from their bodies and 

 limbs, and planted fragments of sponge in their 

 place. Not only does this habit afford the Crabs 

 protective concealment, but it may also in some 

 cases serve as a source of food-supply. The late 

 Dr. David Robertson, of Cumbrae, one of the most 

 observant of marine naturalists, saw the Crab Steno- 

 rhynchus (or Macropodia) longirostris picking food- 

 particles from among the vegetation on its body, and 

 conveying them to its mouth. 



Many Crustacea of different orders seek conceal- 

 ment and protection by burying themselves in sand. 

 A pool left by the tide on a sandy beach may at first 

 sight appear empty of all life, but if it be watched 

 for a little while a greyish, shadowy form may often 

 be seen to dart across it, to settle on the bottom 

 with a little puff of sand, and to disappear. Even a 

 close scrutiny of the spot will hardly discover any- 

 thing, but with a hand-net one may succeed in 

 scooping up, before it can dart away again, a 

 specimen of the Common Shrimp (Crangon vulgaris 

 — see Fig. 78, p. 244), whose translucent body is 

 finely mottled with greyish-brown so as to match 

 exactly the sand among which it rests. 



If a spadeful of sand from between tide- marks be 



stirred up in a bucket of sea-water and allowed to 



settle for a few seconds, and the water then poured 



off through a fine muslin net, a wonderful assemblage 



7 



