March, 1914.] The Food of Rana Pipiens Shreber. 



259 



and covered with a sticky secretion which adheres firmly to the 

 food seized. So rapid is the protrusion of this weapon that a 

 careful watch is necessary in order to see the animal feed. 



The material contained in the stomachs examined can be 

 divided into two classes, animal and foreign. All the evidence 

 indicates that the presence of substances other than those of an 

 animal nature is merely incidental, and due to the mode and con- 

 ditions of feeding. 



Foreign Matter. Nothing can be more natural, since the 

 frog captures the greater part of its prey on the ground by means 

 of its tongue, than that a small amount of foreign substance 

 should be swept into the mouth along with the animals upon 

 which it feeds. In the stomachs examined, this foreign substance 



Collected Aug. 11, 191.3, between 2:00 p. m. and 3:.30 p. m. 



consisted of vegetable and animal matter. Very Httle vegetable 

 matter was found. In four stomachs, it consisted of bits of rotten 

 wood, in eight stomachs, seeds of Washingtonia claytoni Britton, 

 in two stomachs, pieces of Hnden leaves (TiHa americana L.), 

 and in two stomachs, a little spirogyra, the latter being found 

 in stomachs containing aquatic insects. The mineral matter, 

 which consisted of pebbles and sand, composed the greater part 

 of the foreign material. Four small pebbles were found in four 

 stomachs, and about fifteen per cent of the stomachs contained 

 sand, three being completely filled with the latter only. Almost 

 invariably, in the stomach containing sand, the frog had been 

 feeding or preying on animals found on the ground. As the frog 

 swalJpws its prey entire and the stomach does the whole process 

 of trituration, it is probably that the sand aids in grinding the 

 animals, especially insects like beetles with hard chitinous bodies. 



