848 TEXTBOOK OF ZOOLOGY 



factor in learning, and in 1893 announced the famous Canon of Mor- 

 gan. This runs as follows : "In no case may we interpret an action 

 as the outcome of the exercise of a higher psychical faculty if it can 

 be interpreted as the outcome of the exercise of one which stands lower 

 in the psychological scale. ' ' This is merely the law of parsimony ap- 

 plied to animal psychology. While it does not rule out the use of 

 anthropomorphic analogy entirely, it did serve to introduce a measure 

 of restraint into such speculation. This canon was very influential 

 among those, who, while objecting to the extreme view of Loeb, were 

 ready to reject the absurd anthropomorphism of the anecdotalists. 



Two observation methods are used in the study of animal behavior : 

 (1) The genetic method, wherein observations are made upon an ani- 

 mal's behavior as it naturally occurs from the beginning to the end of 

 the life of the animal; (2) The training method, wherein the observa- 

 tions are made upon an animal's behavior during training and after 

 it has been trained in certain habits of action or habits of discrimina- 

 tion among stimuli of different sorts. Every act in an animal's be- 

 havior is a response to one or more stimuli, produced by conditions 

 internal or external to the organism. In the whole phylogenetic series, 

 the internal stimulus is frequently, if not usually, due to the metabolic 

 processes going on constantly within the protoplasm. The restlessness 

 of all organisms is to be ascribed to impulses generated by the meta- 

 bolic processes going on within that organism. An external stimulus 

 is any change in the environment which affects the organism generally, 

 or some special organ or part of it in particular, so that the animal's 

 behavior is modified to some extent at least. No organisms, as a rule, 

 live under conditions that are always the same, i.e., all organisms are 

 subject to the effects of stimuli, and their responses are termed reac- 

 tions. One-celled organisms react to all classes of stimuli that call 

 forth reactions in the many celled organisms. The nervous system and 

 sense organs constitute merely a more delicate, complex, and effective 

 mechanism for the reception of the stimuli to which even the undiffer- 

 entiated protoplasm of Amoeba responds. 



Such stimuli may be classed as chemical, electrical, thermal (heat), 

 mechanical, or photic (light). The reactions of animals to any and 

 aU stimuli are classed as tropisms, reflexes, instincts, and habits. The 

 first three of these are used to connote the many types of native be- 

 havior, whereas acquired activities are spoken of as habits. In so far 

 as these terms imply a sharp distinction between heredity and en- 



