40 FROGS. 



their prey until within range; still others occasionally stalk their 

 prey; and a fourth group, like the tree frogs, may at times leap into 

 mid-air for their game. 



The tongue is the main organ of prehension, but the forefeet are 

 often used in a ludicrous manner to help in forcing into the mouth a 

 difficult or cumbersome object. If one tries to force food or other 

 objects into the mouth of a captive frog, however, the same feet may 

 often be employed to prevent the operation. 



A general summary of the various food elements as thus far deter- 

 mined by previous authors follow^s. 



Vegetable matter. — What Kirkland '^ found true for the toad 

 obtains more or less for our species of true frogs. He held that — 



Vegetable material formed less than 1 per cent and from its character appears to 

 have been taken by accident and can not be properly considered as food. Since the 

 toad takes the greater part of its food from the gi'oimd by means of its large, fleshy 

 tongue, nothing can be more natm-al than that a small quantity of vegetable detritus 

 should be swept into the mouth along with the insects on which the animal feeds. 

 The most common vegetable substance found in the stomachs is grass, both dry and 

 fresh. Bits of rotten wood, broken acorn shells, seeds of the linden ( Tilea americana) 

 and maple {Acer saccharinum) and bits of apple parings have also been detected. 

 All these vegetable substances were usually associated with a large quantity of ants 

 and other terrestrial insects. 



Possibly the more aquatic frogs, like the bullfrog and green frog, 

 might take more vegetable matter than the more terrestrial leopard 

 frog or wood frog. The former have a feeding ground where the 

 algal carpet of the water's surface may be the alighting ground for 

 the prey, or where the wet, broken vegetation of the shore may be 

 the hiding ground of numerous insects. 



Mineral matter. — Of this habit Kirkland writes the following:" 



The mineral matter found in the stomach forms slightly more than 1 per cent of 

 the total contents and consists of gravel, sand, and, in a few cases, coal ashes. When 

 a large piece of gravel is swallowed it is regurgitated ; this I have proven by experi- 

 ments on toads in confinement. Otherwise the gravel passes through the alimentary 

 canal and may be found in the castings. Since the toad does not ^masticate its food, 

 but depends on the stomach for the whole process of trituration, it is probable that 

 the gravel when present assists in grinding the strongly chitinized bodies of beetles, 

 etc., yet in the majority of the toads examined there was no gravel present in the 

 alimentary canal, althoiigh many of the stomachs contained finely ground beetles. 

 A proper inference from the above is that gravel is not essential to digestion in the toad , 

 and the writer inclines to the opinion that, as in the case of the vegetable matter, 

 the presence of gravel in the stomachs is the result of accident rather than of design. 



Animal Matter. — No doubt, in the case of our four principal 

 commercial species this element constitutes from 97 to 98 per cent 

 of the food, as in the toad. 



MoUusks. — Mollusca are seldom eaten by the wood frog and pick- 

 erel frog and constitute about 1 per cent of the food of the toad and 

 about 3 per cent of that of the leopard frog. Mollusca no doubt 

 enter to an appreciable extent into the diet of the more aquatic 

 forms of anurans. Sm'face ^ found the green frog alone had eaten 

 mollusks to any extent, while Dyche" found 12 of his 30 bullfrogs 

 had eaten snails, one having 9 in its stomach. 



Worms. — These enter into the nocturnal toad's diet more than into 

 that of any other species and constitute 1 per cent of its diet. Worms 



a Kirkland, A. H.: Loc. eit., pp. 13-14. 



6 Surface, H. A.: Bi-Monthly Zoological Bulletin. Division of Zoology, Pennsylvania Department 

 of Agriculture. Vol. Ill, No3. 3 and 4. 1913. 



c Dyche, L. L.: i'onds, pond fish, and pond-fish culture, pp. 150-153. State Department of Fish and 

 Game, Kansas. Topeka, 1914. 



