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burrow. The loads of Bind are dumped at the mouth of the hole, the 

 first legs being stretched forward while the sticky mass is pushed from 

 them with the second legs. Where the burrow opens above high tide mark 

 the dirt often accumulates and forms a tower, like that shown in Plate I, 

 which may sometimes be nearly one meter in height. 



The opening of a burrow is iisually closed when it is not being used. 

 On July 4, the writer while sitting within two feet of the ThaJassina 

 tower shown in Plate I saw its owner "close up" for the day. This 

 individual had apparently been digging actively during the night, for 

 a lot of fresh mud had been thro'ivn over the side of the mound. Soon 

 after 10.00 o'clock in the morning he pushed a mass of mud out to 

 within about 12 millimeters of the open mouth; before 10.43 he had 

 brought two similar loads, the first of which was deposited beside the 

 earlier one. As he carried up the last load the whole mass of fresh mud 

 was pushed up from below so that the top of the tower assumed a more 

 or less rounded contour. When a ThaJassina opens a burrow that 

 has been plugged he does not always choose the same place and may 

 leave the old exit as a blind passage ; this is particularly true of burrows 

 in the softer grounds that are covered by the tide (text fig. 2). On the 

 other hand, holes dug in the hard clay of grassy meadows (text fig. 1) 

 often go nearly straight down until they are below water level. Every 

 burrow explored by the writer was of sufficient depth to have standing 

 water in its deeper portions so that it was impossible to follow it on 

 account of the rapidity with which water seeped in. 



