INSTINCTS 209 



these and thousands of other examples might be given. The com- 

 plicated activities of the pronuha moth (see page 38) can be ex- 

 plained only by instinct, and the moth dies without ever seeing 

 her offspring. 



Instincts can best be explained, as many workers with insects 

 have shown, as a chain of reflex acts. For example, an insect's mak- 

 ing a nest, stinging the prey, laying eggs, etc. are a series of in- 

 stinctive acts, each one depending upon the one before. If we 

 interrupt the sequence, as by removing most of the food supply 

 from the nest, or by giving a fly paper soaked in meat juices, 

 instead of rotting flesh, in which to lay its eggs, the life cycle is 

 ended because the insect cannot modify its actions. As Professor 

 Hodge says, a housefly is about as intelligent as a shot rolling down 

 a board. Once the chain of instincts is set in motion by some out- 

 side stimulus, it continues until the life is perpetuated by egg- 

 laying ; thus instincts are, on the whole, beneficial to the race. 



Modification of InvStincts. — Although Fabre (fa'br') found that 

 a certain wasp which instinctively drags its grasshopper prey by 

 one antenna would not touch its prey if both antennae were cut 

 off, yet there are examples of instincts being modified for the 

 benefit of the animal. Some insect larvae, if they have consumed 

 all of the plant on which instinct teaches them to feed, will eat 

 other kinds of leaves and thus save their lives. Fish and frogs 

 can be taught to form new associations, for after many errors 

 they will learn to avoid obstacles placed between them and their 

 food. A dog may refrain from eating a lump of sugar placed on 

 his nose until a word is spoken, because he has formed new nerve 

 connections which considerably change his natural instincts and 

 appetites. 



How Habits are Formed. — Some of our earliest acts are in- 

 stinctive. Babies do not have to be taught to suck ; but as they 

 grow older they modify their instincts. They learn to take food 

 from a bottle and to wait for it. Later on they learn, by a series of 

 trials, to stand erect and then to walk. There is a difference be- 

 tween the instinct of sucking and the habits which are learned 

 later when a new stimulus is substituted for the old one and the 

 child takes other food than its mother's milk. A habit might be 

 called an acquired reflex act. 



