156 REPTILES 



death for ten minutes, while with a little attention they can be 

 induced to remain inert for fully an hour. 



This section of the present volume may be brought to a close 

 by reference to a peculiar digestive adaptation artificially pro- 

 duced by certain reptiles. The fact that the marine plesiosaurs 

 of the Oolitic and Cretaceous were in the habit of swallowing 

 pebbles and retaining them in their stomachs for the apparent 

 purpose of assisting digestion, has long been familiar to palaeonto- 

 logists. Discoveries in America indicate that the great dinosaurs, 

 such as Brontosaurus and Diplodocus, had a similar habit. The 

 evidence rests on the discovery in two instances of small heaps of 

 polished quartzitic pebbles in association with the skeletons of 

 these reptiles. The pebbles are for the most part bright-coloured 

 jaspers, and bear a polish quite different from that of the ordin- 

 ary wind-polished or river-worn pebbles found elsewhere in the 

 same beds, so that they are unmistakable. In the one instance 

 about two dozen were found together, but in the second case the 

 number was smaller. Very curious is the fact that each heap 

 included a certain number of bright-coloured fossiliferous jaspers, 

 which are uncommon in the strata, and suggest that the dino- 

 saurs were in the habit of picking out stones of this particular 

 type for swallowing. A further suggestion is that the stomachs 

 of these pebble-swallowing reptiles were furnished with gizzards 

 like those of birds, as it is otherwise difficult to see how the 

 pebbles can have acted efficiently and been permanently retained 

 in the stomach. 



It may be added that the stomachs of South American 

 caimans, and probably those of other crodilians, frequently 

 contain balls of hair, derived from the animals upon which they 

 have fed. 



