REPORT OF COMMISSIONERS OF INLAND FISHERIES. 197 



to conform to the main requirements of Pfiiiger's law of polar stimu- 

 lation and contraction. 



II. The Mechanism of Reaction, 



We now come to a consideration of the mechanism of reaction on 

 the part of the lobster larvse; and we may express the point of our 

 inquiry in the following terms: By what means, or by what movements 

 of the larvae are the positive or negative orientations accomplished? 



In our effort to answer this question we shall for the present 

 attempt to avoid, so far as possible, all those considerations which 

 deal directly with the ultimate causes of orientation; in other w^ords, 

 we shall limit ourseh-es to the observation of the actual movement oi^ 

 the body, or of certain parts of the body, of individual larvse; and 

 attempt to show what relation exists between these movements and 

 the internal or external factors which appear to determine them. 

 Thus it is merely a matter of convenience that we divide these con- 

 ditions which may determine or modify the behavior of the larvse 

 into the internal and the external factors. Among the former we 

 may include the cumulative effect of all previously acting stimuli; 

 among the latter we may consider the conditions of environment 

 which act directly upon the organism to cause an immediate response. 

 It is the effect of the latter in producing certain kinds of movements 

 of the larvse as a whole, or of their parts, that w^e are now ready to 

 consider. First, however, we must establish some points regarding 

 the natural behavior of the larvse when the reaction to the external 

 stimuli is at the minimum. 



The Normal Behavior of the Larvoe. — Obviously enough we should not 

 be able to recognize certain forms of reaction in the lobster larvse, 

 did we not first have some knowledge regarding what we may call 

 the normal type of behavior. There will be recognized a certain 

 point of difficulty in establishing this basis. What do we mean by 

 natural or normal behavior? Whatever answ-er may be given to 

 this question where the higher animals or man are concerned, for our 



