140 THE FOOD OF ANIMALS 



fathoms, i.e. over 2^ miles from the surface. Some, again, 

 maintain themselves among floating sea-weed, as, for example, 

 the little Gulf-weed Crab {Planes minutus), which is stated to 

 have been pointed out by Columbus to his discontented mariners 

 as a proof of the nearness of land, a good instance of the occa- 

 sional usefulness of fallacious argument. It is also interesting to 

 note that many marine forms have reacquired the power of swim- 

 ming, though not in the old lobster- like fashion, for here pro- 

 gression through the water is brought about by the flattening 

 of the hindmost pair of legs into oars, an arrangement which 

 reminds us of those found in some aquatic insects. This, how- 

 ever, by no means exhausts the possibilities. A number of 

 species, among which must be reckoned the common Shore- 

 Crab (Carcinus mcenas) pick up a living between tide -marks, 

 and there are all gradations between these and thorough-going 

 land-crabs, most of which, however, feed more or less on vege- 

 table matter, and therefore do not fall to be considered under the 



present section. The Swift Land-Crabs 

 {Ocypodidce) (fig. 404) may be instanced 

 as a carnivorous section of the last-named 

 group, living on sandy shores. Stebbing 

 (in A History of Crustacea) speaks of 

 them as follows: — "As the name swift - 

 ^'"- ('o:^,trr'educ"=f "' offoot implies, these Crustacea are espe- 



cially noted for their rapidity of move- 

 ment. They are just the opposite of some of the strong-armed, 

 thick-shelled, slow-moving Cancridcs, i.e. the group of which the 

 common Edible Crab {Cancer pagurus) is a good type. On 

 wind-swept stretches of sandy beach, and coloured like the sand, 

 they sometimes seem rather to be borne on the wings of the wind 

 than to run. Also, with their compressed lancet-like fingers they 

 are extremely dexterous in digging into the sand. They burrow 

 holes an ell deep, generally perpendicular, and from these they 

 wander afar, when the tide is out, in search of food. Krauss 

 observed in South Africa the species Ocypode ceratophthalmus 

 (Pallas) and others, and he says that while they are busy hunt- 

 ing, every now and then they look carefully round, raising their 

 stalked eyes upright, and standing upon tiptoe. At the slightest 

 movement towards them they run with uncommon rapidity to the 

 nearest hole, or, if the danger is too close, press themselves flat 



