638 JONATHAN EISSER 



EXPERIMENTS WITH TADPOLES 

 1. General 



Knauer ('75) emphasizes the fact that some of the larval 

 anurans are less phytophagous than is commonly supposed and 

 instances the fondness of toad tadpoles for animal food. Holmes 

 ('07) also states that decomposing insects, earthworms, etc., are 

 acceptable as food to frog tadpoles. That certain European 

 anurans feed indiscriminately like the earthworm is a well- 

 known fact. Whether vegetable material must not be in the 

 early stages of decomposition before becoming available as 

 food for tadpoles has not yet been determined. It is certain 

 that many unicellular and filamentous algae may be ingested 

 repeatedly before digestion is complete. 



Nagel ('94) denied the olfactory function to aquatic verte- 

 brates. His theoretical objections have been refuted for the 

 fishes by the work of Parker ('10; '11), Sheldon ('11), and Cope- 

 land ('12). The question still remains open as regards am- 

 phibians and its solution depends upon suitable material and 

 methods. This was reason sufficient to attempt an investigation 

 of the olfactory function in the tadpole of the toad. Preliminary 

 trials gave evidence at once that the tadpoles were responsive 

 to the presence of decaying animal matter in their inmiediate 

 vicinity. Tadpoles placed in a vessel containing filtered water 

 for a day or two, the feces being removed frequently, soon come 

 to be in a state of hunger. Water not filtered contained at all 

 times organic material enough to form a delicate film upon the 

 walls of the vessel. This film of partly decomposing organic 

 matter is a source of food for the tadpoles and must be removed. 

 For like reasons the feces must be taken away. 



In the preliminary trials particles of dead earthworms, dead 

 fish or bits of meat undergoing decomposition were placed in the 

 vessel containing the hungry tadpoles Such particles of food 

 were quickly found by the tadpoles. 



The feeding trials were performed on tadpoles of three suc- 

 cessive years. The first set was obtained at Woods Hole, 

 Massachusetts, on August 10, when the tadpoles were about to 



