CRUSTACEA OF THE LAND 189 



gill chambers are adapted to serve as lungs for 

 breathing air, and some species may even be drowned 

 by keeping them in water. The marsh-dwelling 

 or fresh-water Crabs of the genus Sesarma (see 

 Plate XXIII.) and allied genera are also apparently 

 to some extent air-breathers, and one species, Aratus 

 pisonii, is stated by Fritz Miiller to climb mangrove 

 bushes and to feed on their leaves. Some Crayfishes, 

 like the Engceus of Tasmania (see Plate XX.), already 

 mentioned, are practically land animals. Finally, 

 some Amphipoda, closely allied to the Sand-hoppers 

 of British coasts, live in damp places on land, 

 although they do not show any conspicuous modi- 

 fications of structure to adapt them to this mode of 

 life. Of one of these Amphipoda, Talitrus sylvaticu.s, 

 Mr. G. Smith writes : " This species of land-hopper 

 is widely distributed in the highlands of Tasmania, 

 being found under logs and leaves in the forests on 

 Mount Wellington, and in very great abundance in 

 the beech -forests on the mountains of the west 

 coast." 



It will thus be seen that it is impossible to draw 

 any sharp distinction between aquatic and terrestrial 

 Crustacea, and it is chiefly from motives of con- 

 venience that we have left to be dealt with in this 

 chapter three groups of land-dwelling Crustacea 

 the Land Crabs of the family Gecarcinidse, the 

 Land Hermits (Coenobitidse), and the Land Isopods, 

 or Woodlice (Oniscoidea). 



