180 General Biology 



because many animals lay their eggs before they themselves have 

 developed the later characters, which the offspring possess. Conse- 

 quently, the young would have to inherit a habit that the parent was 

 going to form later. This is somewhat like saying that because a 

 mother is divorced, her daughter inherits a desire for divorce from her 

 mother, which, therefore, resulted in the daughter also obtaining a 

 divorce. 



While instincts are made up of reflexes, the reflex proper is said 

 to affect only one part of the organism, while instinct affects the entire 

 body. That is, we should say the winking of the eye, when danger 

 threatens, is reflex, while running away from the danger is instinctive. 



Instincts really consist of inner driving forces which make the ani- 

 mal possessing them restless until the instinctive act is performed. 

 However, we must remember here also that just as with the impulses 

 already mentioned, there may be conflicting instincts. In such cases the 

 stronger will come forth. Or both may be equally strong, so that no 

 action at all will take place. 



Recent psychology often speaks of tropisms. 1 As we have seen from 

 our study of former chapters, a tropism is a movement of some kind on 

 the part of a living organism. Those who wish to interpret all action 

 of living organisms in terms of physics and chemistry are fond of using 

 this term. Such men prefer to cast the term "instinct" to the four winds 

 of heaven and explain everything in physico-chemical terms. They 

 insist that a caterpillar climbs to the end of a twig on account of the 

 chemical change in its body that is caused by hunger, let us say. New 

 chemical molecules and adjustments are forming, and this makes one 

 part of the body lighter than another, so that the laws of physics enter 

 and the heavier part will be followed by the lighter in going downward, 

 or a chemical affinity of some nature will draw the chemical substance 

 of the animal toward it. After having eaten the tiny bud on the twig, 

 a new chemical change takes place and so the animal must, whether 

 it will or not, obey the next chemical and physical change and descend 

 from the twig. 



Dr. Vernon Kellogg, recently in this connection, called attention 

 to a scientific friend who explained to Dr. Kellogg that the reason he 

 took a corner seat in a restaurant was due to a primeval impulse which 

 made him want to have his body in close contact with the wall. But, 

 as Dr. Kellogg says, the reason he chose that particular seat was because 

 he had made an appointment to meet a friend there. 



As the principal test of an animal's mental ability is the rapidity with 

 which it learns, we must know what learning means. Learning means 

 the ability on the part of a living organism to vary its actions according 

 to some definite plan which will show that it has profited by past 

 experience. 



1 Tropisms really mean growth reactions and taxis mean movement, but most writers use tropism 

 to include taxis. 



