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BIOLOGICAL LECTURES. 



behavior or the difficult question of the relation of instinct to 

 habit and intelligence. If the problem is not simplified, its 

 nature is better defined and its perspective is relieved of many 

 a myth that might otherwise obscure our vision. We see at 

 once that the behavior does not stand for a simple and pri- 

 mary adaptation of a preexisting mechanism to a special need. 

 As the necessity for food did not arise for the first time in 

 Necturus, the organization adapted to securing it must be traced 

 back to foundations evolved long in advance of the species. 

 The retrospect stretches back to the origin of the vertebrate 

 phylum, and, indeed, to the very beginning of genealogical 

 lines in protozoan forms. The point of special emphasis here 

 is that instincts are evolved, not improvised, and that their 

 genealogy may be as complex and far-reaching as the history 

 of their organic bases. 



f . Sensibility Sources of Error. 



Another important factor in animal behavior, namely, sensi- 

 bility, is very generally underestimated and often sadly mis- 

 understood. We are apt to gauge sensibility according to the 

 intensity of the overt response to stimulus, forgetting that 

 the animal has the power to inhibit such manifestations or 

 to moderate them in a way to mislead the observer. In the 

 struggle for existence a high premium has been placed on 

 this power, with the result that it is well-nigh a universal 

 attribute. The best proof of its high value to the possessor 

 is our own readiness to accept the disguise it affords as an 

 evidence of lack of sensibility. We are so prone to think that 

 the exercise of such power depends upon considerable intelli- 

 gence that we are incredulous of its existence in forms that 

 give only doubtful signs of intelligence. The power is pos- 

 sessed to a very marked degree by Clepsine, and it is only 

 when we become aware of this fact and take all necessary 

 precautions that we can get any reliable tests of the ani- 

 mal's keenness of sensibility. Necturus is even more difficult 

 to manage, for not until after we have won its confidence by 

 slow degrees can we expect free responses. 



