112 HABITS OF WORMS. Chap. II 



unusual thickness. In this case the worms, 

 judging from the castings, had pushed the 

 cinders away on all sides and had not 

 swallowed any of them. In another place, 

 burrows similarly lined, passed through a 

 layer of coarse coal-cinders, 3| inches in 

 thickness. We thus see that the burrows are 

 not mere excavations, but may rather be 

 compared with tunnels lined with cement. 



The mouths of the burrow are in addition 

 often lined with leaves ; and this is an instinct 

 distinct from that of plugging them up, and 

 does not appear to have been hitherto noticed. 

 Many leaves of tlie Scotch-fir or pine {Pinus 

 sylvestris) were given to woi'ms kept in con- 

 finement in two pots ; and when after several 

 weeks the earth was carefully broken up, the 

 upper parts of three oblique burrows were 

 found surrounded for lengths of 7, 4, and 

 3^ inches with pine-leaves, together with 

 fragments of other leaves which had been 

 given the worms as food. Glass beads and 

 bits of tile, which had been sti'ewed on the 

 surface of the soil, were stuck into the inter- 

 stices between the pine-leaves ; and these 

 interstices were likewise plastered with the 



