INSTINCT AND INTELLIGENCE 437 



they are fortunate enough to attach themselves to the bee they 

 succeed. Otherwise they perish. The female blister beetle is 

 very prolific and deposits many thousands of eggs. Hence it is 

 only necessary that a few of the thousands of larvae should 

 succeed. 



877. Actions like those of the Pronuba, Sphex or blister beetle 

 larva are called instinctive. They are not prompted by a kind 

 of intelligence. Nor are they in any sense akin to intelligence, 

 though among the higher animals it is often difficult to say 

 whether an act is prompted by instinct or intelligence. 



878. If a moth habitually rests on surfaces which it resembles it 

 does so instinctively, not because it has an intelligent compre- 

 hension that it is thereby protected. When a caterpillar spins 

 a cocoon it does so instinctively and not with the forethought of 

 providing protection. When a young bird builds a nest it is 

 impelled thereto by instinct, and the form and manner of build- 

 ing the nest are also determined by instinct. In the latter case 

 more or less evidence of intelligence may be discernible, but the 

 process as a whole is instinctive. 



879. An instinct is a kind of adaptation and subject to the laws 

 of heredity. Instinctive actions may, therefore, be developed 

 under natural selection, just like other adaptive characters of 

 an organism. 



880. Intelligence. Intelligence is found only among the most 

 highly organized animals because it is dependent upon an 

 efficient set of sense organs which yield accurate information 

 concerning the environment, a flexible response mechanism 

 which may react in multitudinous ways to the infinite 

 variation in the conditions of existence, and an organ of con- 

 trol, the brain. In practically all Birds and Mammals the first 

 two of these conditions ^intelligence are well met, and yet there 

 is a vast difference in intelligence within these classes. This is 

 due to the difference in brain structure. The brain of the lowest 

 Vertebrates is an inconceivably complex organ, and in the higher 



