Chap. III. BROUGHT UP BY WORMS. 167 



rolled with a heavy agricultural roller fifty-two 

 days before, and this would certainly have 

 flattened every single casting on the land. 

 The weather had been very dry for two or 

 three weeks before the day of collection, so 

 that not one casting appeared fresh or had 

 been recently ejected. We may therefore 

 assume that those which were weighed had 

 been ejected within, we will say, forty days 

 from the time when the field was rolled, — 

 that is, twelve days short of the whole inter- 

 vening period. I had examined the' same 

 part of the field shortly before it was rolled, 

 and it then abounded with fresh castings. 

 Worms do not work in dry weather during 

 the summer, or in winter during severe frosts. 

 If we assume that they work for only half 

 the year — though this is too low an estimate 

 — then the worms in this field would eject 

 during the year, 8*387 pounds per square yard; 

 or 18*12 tons per acre, assuming the whole 

 surface to be equally productive in castings. 



In the foregoing cases some of the 

 necessary data had to be estimated, but in 

 the two following cases the results are much 

 more trustworthy. A lady, on whose ac- 

 curacy I can implicitly rely, offered to collect 



