LULU F. ALLABACH. 



What is the cause of the change of behavior in these experi- 

 ments ? Several possibilities suggest themselves : 



1. Jennings (1905) found that in Aiptasia similar effects were 

 produced, and in this case the result was evidently due mainly to 

 changes in the state of hunger. The very hungry Aiptasia took 

 meat and paper readily, but after feeding a -short time it refused 

 paper, and later it came to refuse meat also. The animal could 

 be caused to refuse paper more readily by feeding it meat alone 

 than by feeding paper alone or by feeding the two in alternation. 

 It was evident that the changed reaction toward paper was due 

 to loss of hunger. We must inquire whether this factor plays a 

 part in Metridium. 



2. Nagel (1892) referred the changes in reaction toward paper 

 to a process corresponding to what we call judgment in higher 

 animals ; he held that the animal discovers by experience that 

 the paper is unfit for food, and thereafter refuses to take it. Such 

 a process in so low an animal would of course be of great 

 interest, and the evidence for it needs to be examined carefully. 

 Nagel held that it was owing to the lack of close nervous inter- 

 relation of parts in these animals that the experience of one side 

 is not transmitted to the opposite side. 



3. Parker sums up the phenomena shown in these experiments 

 as follows : " The successive application of a very weak stimulus 

 is accompanied, not by the summation of the effects of stimula- 

 tion, but by a gradual decline in these effects, till finally the 

 response fails entirely" (Parker, 1896, p. 116). 



In my experiments I attempted to test these different possi- 

 bilities, and to work out in a systematic way the various factors 

 which modify reactions in Metridimn. 



The taking of food has been well described by Parker (1896). 

 It is important to note that ciliary action plays a large part in the 



