m 



NOTE: A. Diagram of the reconstructed sequence of new burrow building 

 (burrows nos. 2 and 3) by a single wornn, with collapse of original burrow (No. 

 1). "A", anterior, "P", posterior; direction of movement. B. Diagram of the 

 vertical burrow network developed by a single worm and its persistence over 

 time(18°C). 



309 



