318 ASA A. SCHAEFFER 



controlled as those naturally resident in an animal. When 

 it is remembered that peculiarities of movement of a food organ- 

 ism may be a factor in discrimination, thic consideration ac- 

 quires added significance. 



The Rana clamaia was fed with an irregular succession of 

 earthworms and mealworms {Tenebrio obscura and T. molitor) 

 for a few days to determine whether either of these organisms 

 is eaten with greater readiness than the other. After it was 

 found that if any such preference existed, it was in favor of 

 the earthworm, the earthworms that were fed henceforth were 

 nearly all treated with oil of cloves or with calcium chloride. 

 These chemicals markedly irritate the mucous membranes 

 of the frog. It was thought that the frog would in time come 

 to leave the chemically treated worms alone. The experiment 

 was not entirely perfect in its technique because the oil of cloves 

 and the calcium chloride caused the wonns to behave abnormally. 



These substances are very irritating to the worms, causing 

 violent movements, and if the substances act for a few minutes 

 the worm becomes paralyzed in the treated region; for this 

 reason only the posterior parts of the worms were treated. 

 However, since only confirmatory evidence was wanted — evi- 

 dence derived from a method of experimentation different in 

 nearly all respects from that employed in the first series of 

 experiments — only the general results need be regarded. These 

 proved to be satisfactory. The following is a summary of the 

 results obtained from feeding the medium sized green frog 

 with meal worms and an occasional chemically treated earth- 

 worm. 



First day. I painted the posterior part of an earthworm 

 with a little oil of cloves, and placed it into the cage. The worm 

 wriggled less than a normal worm. The frog snapped it up in 

 normal fashion. There was no indication that it experienced 

 any disagreeable sensations. 



Second day. 11.30 a. m. I painted several worms with oil 

 of cloves and placed them into the cage in clear view of the 

 frog. None were eaten or reacted to in any way for 5 minutes. 

 I then put a small meal worm into the cage. This was eaten 

 in 15 seconds. In a few minutes a chemically untreated earth- 

 worm was put into the cage. It was eaten in about 30 

 seconds. 



