342 THE LIOLOGY OF THE FROG CHAP. 



CHAPTER XVIII 



INSTINCTS AND TROPISMS AS RELATED TO REFLEX 



ACTION 



WE have already treated of some of the reflex actions of 

 the frog and have shown that they exhibit a purposive char- 

 acter, often in a very striking degree. They are far from 

 being mere random responses to stimuli ; notwithstanding 

 the fact that they may take place independently of intelli- 

 gent control. It is generally recognized that there is a 

 close connection between reflex actions and instincts, it 

 being, in fact, very difficult to draw the line between them. 

 The behavior of an animal is usually called instinctive when 

 it takes place without previous instruction and with no con- 

 sciousness of the end to which it is directed. A digger wasp, 

 for instance, makes a nest of a particular type in the ground, 

 catches only certain species of insects, which it stings in the 

 ventral ganglia, so as to produce paralysis without causing 

 death, and, after depositing an egg upon it, buries its prey 

 in the nest as provision for its future offspring. The wasp 

 is utterly unconscious of the significance of its complex 

 behavior ; of the wriggling grub which it has labored so 

 industriously to provision it knows nothing and cares less ; 

 it is impelled by blind impulses to a particular line of activ- 

 ity, which, although of no service to the individual wasp, is 

 essential to the continuance of the race. It is guided neither 

 by previous experience nor by imitation, and has no basis 

 for drawing any conclusion regarding the utility of its con- 



