704 RAYMOND FKARF;. 



signiticiiiK-0 of such a condition is always realised. It implies 

 that the animal as an individual " does '^ nothing in the sense 

 that a man " does " things. It is moved about from place to 

 place by its locomotor organs ; it is put into certain definite 

 and invariable relations to its surroundings by its reflex 

 mechanisms. Considered as a whole, such an organism is a 

 sort of shell to hold a series of mechanisms, each of which is 

 independently caj^able of doing a certain thing, and in the 

 doing produces some effect on the shell as a whole. We may 

 perhaps get a clearer picture of what such a reflex existence 

 means by considering for a moment what Avould be the effect 

 if all a man's activities were composed of invariable reflexes, 

 to be set off by the appropriate stimuli. Under such circum- 

 stances, whenever a man saw or smelled food he would have 

 to go to it and eat it. Whenever anything touched him he 

 would have to move in a new direction very closely related 

 to the position of the object which touched him. Whenever 

 he touched water he would have to take a bath, or perhaps 

 drink till he could hold no more. During the day he would 

 have to move always in a definite direction with reference to 

 the sun, and so on ad infinitum. All he did Avould be 

 definitely fixed and, in a sense, predetermined b}^ the things 

 about him. 



It is apparent that the behaviour of Planaria is not thus 

 entirely and purely reflex, because there is a certain amount 

 of variation in it. As has been brought out in several places 

 in the body of the paper, and in paragraph 10 of these 

 conclusions, this variation in the behaviour is the result of 

 the physiological condition of the individual. To put this in 

 a more concrete form, we may say that a fatigued animal 

 or an animal in a state of great excitation docs not always 

 react to a certain stimulus by the same set of reflexes as that 

 by which a normal animal would react. Furtliermore, there 

 is a variation in the intensity of the negative reaction 

 dept'iideiit upon the intensity of the stinnilus producing it. 



Another point in which the reactions of Planaria dilTer 

 from what would obtain in the case of an oro-anism whose 



