500 GENERAL CONSIDERATIONS 



cocoons of this particular species are similar; they bear the stamp of the 

 species just as clearly as does the adult insect. To one acquainted with 

 silkworm cocoons that of each species is characteristic of the species to 

 which it belongs. The caterpillar needs no teaching. The results are 

 perfectly adjusted to the needs of the case. This adaptation of particular 

 instincts to the particular conditions involved is so perfect that it has 

 been likened to the relationship between the key and the lock which it 

 fits. Yet it is clear that there can be no forethought or anticipation of 

 results on the part of the animal. To many who are not students of 

 animal behavior this perfect adjustment seems to prove the presence 

 of intelligence. 



Other striking instincts are concerned with the securing of food and 

 with mating, nest-building, and other reproductive activities, especially 

 of the arthropods. 



From what has been stated it is clear that instincts are inherited and 

 this inheritance seems to involve a certain structure in the nervous 

 system. This structure has sometimes been referred to as an action 

 pattern. It can be said that any particular animal inherits a certain 

 action pattern which, when it is brought into play under proper condi- 

 tions and by the appropriate stimulus, leads to results which are always 

 the same for any individual belonging to the same species as the animal in 

 question. Instincts as such are, therefore, not subject to modification 

 unless they are involved in the process of evolution, for they have evolved 

 in the same way as have the structural characteristics of the species and 

 the other functions which depend upon these structures. 



523. Habits. — Reference has been made to the development of habits 

 in the starfish (Sec. 229) and in the frog (Sec. 392). To a certain degree 

 a habit resembles an instinct and it is this resemblance which gave rise to 

 the former impression that instincts are inherited habits and has sug- 

 gested the idea that habits are lapsed instincts. The two, however, may 

 be sharply separated in certain ways: (1) Habits are individual and not 

 specific. (2) They are formed during the lifetime of the individual which 

 possesses them. (3) They are not transmissible to the next generation. 



A habit is acquired as a result of repeated action. This repetition 

 may have to occur only a moderate number of times or it may need a 

 considerable number. Nevertheless it is clearly the result of an action 

 repeated many times under the same conditions, which has had such an 

 effect upon the nervous system that, with the aid of memory, the action 

 is again repeated when similar conditions arise. A habit may be gradu- 

 ally developed and gradually modified. It has some of the characteristics 

 of an instinct in that it needs a certain stimulus to bring it out and that it 

 frequently fits very perfectly certain conditions. At times habits will 

 simulate instincts very closely but the two may be differentiated when 

 other individuals of the same species are brought into comparison. The 



