Organs of Nutrition 137 



where they had l)e('ome scattered, each jiirouj) covered 

 only a few square yards of ground, and in that s|)ace 

 hiy thickly strewn. . . . The peculiai- featiu'e of tlie 

 stones was that they were almost all opaque, white (juarlz 

 ])ebhles. In one place I found a small group of small 

 pebl^les of diftcrent colour, more like the few l)rown water- 

 worn pebbles which may be picked up hereabouts. 'Jliese 

 lay with a set of l)ones much smaller than the veiy large 

 bones I found with most of the clusters of pel)bles. 



"I did not gather these brown pel)l)les, as 1 thought 

 it uncertain wdiether they were gizzard-stones or not, 

 though it is [)ossible that the species to which the smaller 

 stones belonged was not so careful in selecting white 

 stones. 



''A ghmce at the j^ebbles lying around in the sur- 

 rounding country showed that the quartz-j)ebl)les were 

 not collected here. . . . Mr. Murdock and 1 collected 

 three sets of ])ebl)les, and these 1 can ])i'()nounce coni- 

 j)lete, or nearly so. It is beyond cjuestion, too, tliat each 

 set belongs to a distinct bird. No. 1 weighs o lb. 9 oz.; 

 No. 2 weighs 4 \h.; while No. 3 weighs no less than 5 lb. 

 7oz.! Tins giant set contains individual stones weighing 

 over 2 oz.; indeed, I have picked out eight stones weigh- 

 ing almost exactly 1 pound." 



The gizzard of a l)ird is reflective of its diet, and is 

 very quickly affected by any change in the food. For 

 example, a ca])tive gull when fed exclusi\ely on fish 

 has but little muscular ])0wer in the gizzaixl, but a diet 

 of grain will ])roduce a change in that organ, giving it 

 grinding power sufficient to crush the kernels of corn. 



