106 INSTINCT 



The clasping of the female frog by the male during the 

 breeding season affords a typical example of instinctive 

 behavior; nevertheless, it occurs hi entire independence of 

 the higher nerve centers. "The Abbe Spallanzani showed 

 that a male frog may have its head cut off during copulation 

 without ceasing to cling tenaciously to the female. Goltz 

 went still further and cut off the head of a male, then cut the 

 body through between the third and fourth vertebrae, and 

 removed the viscera from the body cavity; the section of the 

 frog that remained after these operations consisted of the 

 first three vertebrae, the pectoral girdle and the fore legs. 

 Yet when the skin of the inner surfaces of the fore legs was 

 rubbed with the finger this segment would show the same 

 clasping efforts as a normal male frog." 



Nearly all the characteristic responses of the frog will take 

 place in individuals deprived of the cerebral hemispheres 

 which are the part of the brain usually considered as the 

 seat of intelligence and volition. Such a frog, if given suffi- 

 cient time to recover from the shock of the operation, will 

 leap about and swim spontaneously, snap at insects which 

 come within range, bury itself in the mud on the approach 

 of winter, and in many other ways behave in a normal 

 ranine manner. 



Beginning with the anterior part of the brain and destroy- 

 ing successively the parts of the central nervous system 

 lying behind it, we cause, one after the other, the various 

 instinctive acts of the frog to disappear, until we have left 

 only the reflexes of the posterior part of the spinal cord. We 

 reduce the frog to a more and more simple type of reflex 

 mechanism, but we cannot say where the animal ceases to 

 be more than a reflex mechanism of a complicated kind. 

 The behavior of the frog is almost entirely made up of in- 

 stinctive and reflex acts, many of which have their seat 



