n6 Instinct and Intelligence 



lungs, and have developed specialised olfactory 

 sensory organs. To a large extent, however, 

 this class of animals has to depend on their 

 visual apparatus to enable them to gain their 

 supply of food and to warn them of approach- 

 ing danger. Their central nervous system has 

 evidently responded to this demand, for it has 

 become so far developed as to enable the 

 Amphibia to appreciate between differences in 

 colour. This is demonstrated by forcing a frog 

 to follow a certain track in a labyrinth in order 

 to obtain a supply of food. 1 At a point in the 

 labyrinth where a choice between the right and 

 wrong paths was necessary " a red card was 

 placed on one side and a white card on the 

 other side. When the frog had learned to take 

 the correct path towards the white, the cards 

 were exchanged without any other alteration 

 in the conditions, and the decided confusion of 

 the animals indicated that they had dis- 

 criminated between the red and white cards, 

 and had learnt to react with reference to this 

 discrimination." The small green tree-frog, 



1 Journal Com/). Neur. and Psych., Vol. XV., p. 279. 



2 The Animal Mind, by M. F. Washburn, p. 142. 



