258 BEHAVIOR OF THE LOWER ORGANISMS 



so that they responded to the dark screen alone by the reaction proper 

 to food. We shall analyze these phenomena more fully in our general 

 discussion of behavior (Chapter XVI). 



These processes, by which behavior becomes more or less enduringly 

 modified, are known to play a large part in the behavior of higher inver- 

 tebrates, such as ants and bees, and in the vertebrates. As investigation 

 progresses, we find analogous processes lower and lower in the animal 

 scale. It was only eight years ago that Bethe (1898) could deny their 

 occurrence even in ants and bees ; now they have been fully demonstrated 

 in these and much lower animals. The study of these matters has hardly 

 begun, and it is not too much to say that no experiments have been 

 carried through on the lowest invertebrates that would show this lasting 

 modifiability, even if it exists. We are therefore still in the dark as to 

 how far downward such modifiability extends; time may show it to be 

 a universal property of living things. 



The importance of this modifiability for the understanding of behavior 

 is obviously great. Where such modifiability exists, the definite " reflex" 

 is not to be considered a permanent, final element of behavior. On the 

 contrary, it is something developed, and it must differ in individuals 

 with different histories. Two specimens of Convoluta side by side might 

 show at the same moment, one "positive geotropism," the other "nega- 

 tive geotropism," depending on their past history. Whether a hermit 

 crab will pass beneath a dark screen, or will avoid it, is not determined 

 by the permanent properties of its colloidal substance; this can be pre- 

 dicted only by knowing the history of the individual. 



The process by which an organism acquires a definite reaction which 

 it before had not is, of course, nothing mystical, but an actual physio- 

 logical one, whose progress is open to investigation as is that of any other. 

 It needs to be studied and analyzed in the same objective way as the 

 circulation of the blood. The power of changing when acted upon by 

 outer agents, in such a way as to react differently thereafter, is one of the 

 most important properties of living matter, and it is misleading to ignore 

 this property and deal with animals as if their reactions were invariable. 

 How the modifications occur is one of the fundamental problems of 

 physiology. We must remember that even what we call memory, in- 

 telligence, and reasoning are composed objectively of certain physio- 

 logical processes. In other words, as Liebmann has emphasized, there 

 are objective material processes that follow the laws of intelligence, of 

 reasoning, of logic. This is a capital fact. In searching for the laws of 

 life processes we must remember that those just mentioned are as real as 

 any others, and their laws must be provided for in the physics and 

 chemistry of colloids if these are to give us the laws of life processes. 



