CARNIVOROUS CRUSTACEA AND KING-CRABS 141 



on the sand till an attempt is made to seize them, and then off 

 they dart. In running they carry their bodies high, doubling and 

 dodging with such speed and cunning that it is a difficult matter 

 to lay hold of them. When the tide comes up they are enclosed 

 in their flooded burrows, and as soon as the waves retreat they 

 are busily employed in clearing them, shovelling out the wet sand 

 and heaping it at some little distance off. The American species, 

 Ocypode arenaria (Catesby) is described by Professor S. I. Smith 

 as having precisely similar habits. According to his observation, 

 it lives largely upon the amphipods of the genus Talorchestia, 

 known as 'beach-fleas', which inhabit the same localities. 'It 

 will lie in wait ', he says, ' and suddenly spring upon them, very 

 much as a cat catches mice. It also feeds upon dead fishes and 

 other animals that are thrown on the shore by the waves." It 

 may be finally noted that some Crabs are inhabitants of fresh 

 water. 



MANTIS SHRIMPS (Stomatopoda). In such a typical member 

 of this group as the common Mantis Shrimp (Squilla mantis) 

 (see vol. i, p. 411), found to some extent in British seas, the 

 structure is clearly adapted to a predaceous life. The feelers 

 and stalked eyes are well developed, and there are powerful 

 seizing organs. These are not, however, the same pair of special- 

 ized appendages as in a lobster, but correspond to the second 

 pair of foot-jaws in that animal (vol. i, p. 406). But here, instead 

 of three pairs of jaws and three pairs of foot-jaws, we find two 

 extra pairs of the latter. The seizing organs do not end in 

 pincers, but, as in several cases already described, have a blade- 

 like end-joint which can be bent back on the rest of the limb. 

 Mantis Shrimps excavate deep burrows in the zone below low- 

 tide mark, and lie in wait for prey at the mouths of these. 



HIGHER CRUSTACEA SESSILE-EYED FORMS 



(EDRIOPHTHALMATA or ARTHROSTRACA) 



The Sessile-eyed Crustacea (Edriophthalmata) derive their 

 name from the fact that the eyes project directly from the head 

 instead of being situated on stalks as in the forms so far con- 

 sidered. The large majority of them are to be found in shallow 

 water and on the shore, and are by no means restricted to salt 

 water. Many of them play an important part in scavenging 



