Organs of Nutrition 137 



where they had become scattered, each group covered 

 only a few square yards of ground, and in that space 

 lay thickly strewn. . . . The peculiar feature of the 

 stones was that they were almost all opaque, white quartz 

 pebbles. In one place I found a small group of small 

 pebbles of different colour, more like the few brown water- 

 worn pebbles which may be picked up hereabouts. These 

 lay with a set of bones much smaller than the very large 

 bones I found with most of the clusters of pebbles. 



"I did not gather these brown pebbles, as I thought 

 it uncertain whether they were gizzard-stones or not, 

 though it is possible that the species to which the smaller 

 stones belonged was not so careful in selecting white 

 stones. 



"A glance at the pebbles lying around in the sur- 

 rounding country showed that the quartz-pebbles were 

 not collected here. . . . Mr. Murdock and I collected 

 three sets of pebbles, and these I can pronounce com- 

 plete, or nearly so. It is beyond question, too, that each 

 set belongs to a distinct bird. No. 1 weighs 3 Ib. 9 oz.; 

 No. 2 weighs 4 Ib.; while No. 3 weighs no less than 5 Ib. 

 7 oz. ! This 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 bird is reflective of its diet, and is 

 very quickly affected by any change in the food. For 

 example, a captive gull when fed exclusively on fish 

 has but little muscular power in the gizzard, but a diet 

 of grain will produce a change in that organ, giving it 

 grinding power sufficient to crush the kernels of corn. 



