178 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



ful, for instance, the flying of the moth into the 

 flame. 



In many cases the greater complication of instinctive 

 actions compared with simple reflex actions is due to the 

 fact that in the instinctive actions we have to deal 

 with a chain of reflexes in which the first reflex be- 

 comes at the same time the cause which calls forth 

 the second reflex. The taking up of food by the 

 frog is a good illustration of this. The motion of the 

 fly causes an optical reflex which results in the snap- 

 ping motion. The contact of the fly with the mucous 

 membrane of the pharynx sets free a second reflex, the 

 swallowing reflex, which brings the fly into the ceso- 

 phugus. If it be true that the instincts belong to the 

 same class of processes as the reflexes, their relation to 

 the central nervous system should be the same. We 

 have seen that as far as reflexes are concerned, the 

 nervous system only acts as a protoplasmic conductor 

 between the periphery (sense organs) and the muscles. 

 I think it is possible to show that this is also true for 

 instincts. In order to prove this, we shall have to go 

 into an analysis of the instincts. We shall select for 

 our analysis such simple cases of instincts as depend 

 upon tropisms. 



2. We have seen that when certain Crustaceans, for 

 instance Palsemonetes, are subjected to the effect of a 

 galvanic current such changes of tension take place in 

 the muscles of the appendages that movement toward 

 the anode becomes easier, and toward the kathode 

 more difficult. The result is that if the current is 



