LAND CRUSTACEANS. 95 



genus, is used, in 0. macrocera at least, to warn out intruders. They differ somewhat in 

 construction with the age of the inhabitant. The full-grown crab, of the sage-green and 

 yellow coloration, makes a hole two or three feet deep with a spiral inclination of about 

 one and a half turns either to the right or to the left indifferently. The burrow grows 

 smaller from above downwards and, in the largest examples, has at the top a sort of 

 vaulted chamber excavated in the sloping beach and leading downwards on one side into 

 the spiral. In this chamber the crab may sometimes be seen sitting. The younger 

 individuals, of a paler, whitish tint and with undeveloped horns on the eyestalks', make 

 tubular holes at right angles to the surface of the sand and usually curving to one side or 

 the other at the bottom — the beginning, perhaps, of the spiral of older individuals. There 

 is often a small second opening to these burrows, which thus become roughly U-shaped. 

 When an attempt is made to dig out the crab, it escapes by the smaller opening if one be 

 present. If not, it makes a bolt to get out past the intruder. The larger individuals 

 usually prefer to retire to the bottom of the hole and fight it out. 



In digging its burrow, the crab brings up armfuls of sand between the chelae and 

 the body, and throws it away at some little distance from the opening, thus making a 

 low mound, and of course burying any object that may have been there. This process 

 being repeated twice a day by a large number of crabs, a very considerable amount of 

 sand is thus turned over-, and the burrowing of these creatures must tend in the long 

 run to the same end as that of earthworms — namely to the gradual sinking of any object 

 originally lying on the surface to the level of the bottom of the burrows. That this really 

 happens is shown by the fact that, in digging through the sand, one comes across objects that 

 must have originally lain on the surface, and are now sunk to varying depths. This is the 

 case not only with coral stones but with leaves, sticks, etc., often fresh and of recent burying 

 at a considerable depth. In this connection it must, of course, be borne in miml that the 

 food of the crabs consists largely of leaves and seaweed, which they are in the habit of 

 carrying with them into their burrows^. They do not, however, do this with sticks, and a 

 large mass of mammalian dung, found intact at a depth of about a foot in the sand, points 

 to the same conclusion as the sticks. The larger holes reach a layer of coral pebbles inter- 

 spersed in places with twigs, but in one locality Mr Stanley Gardiner found a mass of decaying 

 vegetable matter containing earthworms. This probably consisted largely of material carried 

 by the crabs to the bottom of their burrows for food. 



It is possible that, in addition to their vegetable food, these crabs may be in the 

 habit of catching and eating sandhoppers in the same way as G. arenaria (Catesby)^ I 

 have not been able to see them do this, but some small individuals, shut up in a bottle 

 with some sandhoppers and a little sand, caused the Amphipods to disappear in the course 



' These horns, from which the species takes its name, are, 10 ozs. Positions selected quite at random, at too great a 



of course, well known to be of very variable length in the distance to allow me to see whether they contained any holes 



adult. or not." 



- I am indebted to Mr Stanley Gardiner tor the following ' One or two leaves or pieces of seaweed may often be 

 figures, which he very kindly obtained for me after my found in the burrows, but I have never come across any- 

 leaving the Island. " Observations in 14 places between thing like a lining of these materials. The destruction of 

 Lighthouse and west end of island. Lagoon shore. In the burrows by the tide would probably prevent this, 

 areas of 5 sq. yds., greatest number 28 holes; least 2; aver- '' S. I. Smith, cited by Stebbing, "Crustacea," p. 86, 

 age 14 — 15; sand thrown out twice in 25 hrs. Weight of London, 1893. 

 sand from 12 large holes 19 lbs. 3 ozs. ; average weight 9 — 



