CRUSTACEA OF THE SEASHORE 95 



These also preserve some traces of the original 

 twisting of the abdomen, and have swimmerets only 

 on one side. 



Some Crustacea construct habitations for them- 

 selves. On turning over a flat stone between tide- 

 marks, one often finds a little mass of bits of weed 

 and rubbish attached to it, and if this be torn open 

 a greenish-brown, shrimp-like animal, about three- 

 quarters of an inch long, is seen slithering away on 

 its side. This is an Amphipod {A mphithoe rubricata) 

 which builds the shelter for itself, sticking the frag- 

 ments together with threads of a cementing material 

 produced by glands on the surface of its body and 

 legs. Other Amphipods construct more neatly 

 finished tubular dwellings of mud, or even of small 

 stones, which are attached to sea-weeds and the like ; 

 and some make portable shelters of the same kind, 

 which they carry about with them like the caddis- 

 worms of fresh-water streams. 



Some of the true Crabs also employ portabje 

 shields for purposes of defence or of concealment. 

 The species of Dorippe which are found in tropical 

 seas have the last two pairs of legs short, elevated 

 on the back so that they cannot be used for walking, 

 and ending in a kind of grasping claw. By means 

 of these claws the Crab holds over its back some 

 object, generally one valve of a molluscan shell, 

 sometimes even a mangrove-leaf, to supplement the 

 protection afforded by its carapace. The *' Sponge 



