THE HIGHER ORGANISMS 169 



ciently clear cut to make it possible to say when one 

 ends and another begins. In such a series we observe, 

 in ascending order, tropisms, reflexes, instincts, associa- 

 tion of ideas, memory, intelligence, consciousness, self- 

 consciousness, and reason. 



Loeb and Jennings find it impossible to clearly separate 

 tropisms, reflexes, and instincts; T. H. Morgan seems to 

 regard tropisms and instincts as identical; Herbert 

 Spencer, who defines instincts as "compound reflex ac- 

 tion," sees no clear line of demarkation between instinct 

 and reflex action, and Parmelee believes that there is a 

 strict continuity between all these different forms of 

 behavior, and that the more complex are built up upon 

 the simpler. 



All of these manifestations of vital activity are col- 

 lectively known, as behavior, and behavior of whatever 

 kind is based upon structure. James says "instincts are 

 the correlatives of structure." 



As the structural development of every creature is the 

 result of its inheritance, so its behavior also results from 

 heredity. As we believe that structural modifications 

 were gradually developed, so we believe that behavior 

 was gradually developed to the point at which we find it. 

 If, however, through sudden mutation the structure of 

 an animal could suddenly change, it is conceivable that 

 its behavior might change correspondingly, an old in- 

 stinct being lost or a new instinct developing. 



This is born out by what we observe among animals in 

 whose life history distinct changes occur and require a 

 whole new series of instincts to determine behavior. 

 Thus instinct in a caterpillar determines that it hold 

 tenaciously to the twig whose leaves it eats, move from 

 twig to twig as the leaves are consumed, eat voraciously 

 until of full size, and then spin a cocoon of complicated 

 weaving, and of a pattern common to all its kind, in which 

 it imprisons itself to rest during the chrysalis stage and 

 from which it emerges an imago. The imago or moth 

 seems to know nothing of the instincts of its larval stage, 



