i 36 The Bird 



in a chicken, is in shape like a double convex lens. The 

 cavity in the centre is lined with a tough yellow membrane, 

 sometimes almost as hard as bone. Two great tendons 

 spread over the outer surface on each side, and although 

 in life forever buried in the absolute darkness of the 

 bird's body, yet when brought into sunlight they shine 

 with an iridescence like the beam from a spectrum. 



It is hardly possible for the gizzard to grind up food 

 in the sense of having much lateral motion, like the move- 

 ment of the jaws in chewing, but it shuts together again 

 and again with great force. Gravel and sharp stones are 

 swallowed by many birds, and are of great importance 

 in helping to grind the food. The number and size of 

 these stones are sometimes almost beyond belief. I 

 have known a cassowary to swallow over a quart of rubble 

 in one day, and have given a quartz pebble twice as large 

 as a hen's egg to one of these birds and watched it slip 

 down the bird's throat as easily as a cube of carrot. This 

 particular bird preferred smooth white quartz pebbles, 

 and would search through a whole heap, picking out stones 

 of this character. The same preference was exhibited 

 by the gigantic extinct birds of New Zealand called moas. 



Mr. Frederick Chapman, writing of a portion of New 

 Zealand where the skeletons of moas were found in great 

 abundance, says: "When we came upon the ground 

 disturbed by the wind (the soil being shifting sand) 

 we soon found a number of distinct groups of gigantic 

 gizzard-stones. It was impossible to mistake them. In 

 several cases they lay with a few fragments of the heavier 

 bones. In all cases they were in distinct groups; even 



