Chap. VI. AIDED BY WOKMS. 267 



still be detected. On another occasion, after 

 rain which was never heavy, but which lasted 

 for 18 hours, all the castings on this same 

 gently inclined lawn had lost their vermiform 

 structure ; and they had flowed, so that fully 

 two-thirds of the ejected earth lay below the 

 mouths of the burrows. 



These observations led me to make others 

 with more care. Eight castings were found on 

 my lawn, where the grass-blades are fine and 

 close together, and three others on a field with 

 coarse grass. The inclination of the surface at 

 the eleven places where these castings were 

 collected varied between 4° 30' and 17° 30'; 

 the mean of the eleven inclinations being 

 9° 26'. The length of the castings in the 

 direction of the slope was first measured with 

 as much accuracy as their irregularities would 

 permit. It was found possible to make these 

 measurements within about ^ of an inch, but 

 one of the castings was too irregular to admit 

 of measurement. The average length in the 

 direction of the slope of the remaining ten 

 castings was 2*03 inches. The castings were 

 then divided with a knife into two parts along 

 a horizontal line passing through the mouth 



