216 The Outline of Science 



ticular emotions beyond the immediate circle of sex emotions 

 of joy and of fear, of jealousy and of contentment. Finally, we 

 judge, the animal perhaps the bird was first began to give 

 utterance to particular "words," indicative not merely of emo- 

 tions, but of particular things with an emotional halo, such as 

 "food," "enemy," "home." Long afterwards, words became in 

 man the medium of reasoned discourse. Sentences were made 

 and judgments expressed. But was not the beginning in the 

 croaking of Amphibia? 



Senses of Amphibians 



Frogs have good eyes, and the toad's eyes are "jewels." 

 There is evidence of precise vision in the neat way in which a frog 

 catches a fly, flicking out its tongue, which is fixed in front and 

 loose behind. There is also experimental proof that a frog dis- 

 criminates between red and blue, or between red and white, and 

 an interesting point is that while our skin is sensitive to heat rays 

 but not to light, the skin of the frog answers back to light rays 

 as well. Professor Yerkes experimented with a frog which had 

 to go through a simple labyrinth if it wished to reach a tank of 

 water. At the first alternative between two paths, a red card was 

 placed on the wrong side and a white one on the other. When 

 the frog had learned to take the correct path, marked by the white 

 card, Prof. Yerkes changed the cards. The confusion of the 

 frog showed how thoroughly it had learned its lesson. 



We know very little in regard to sense of smell or taste in 

 amphibians ; but the sense of hearing is well developed, more de- 

 veloped than might be inferred from the indifference that frogs 

 show to almost all sounds except the croaking of their kindred 

 and splashes in the water. 



The toad looks almost sagacious when it is climbing up a 

 bank, and some of the tree-frogs are very alert ; but there is very 

 little that we dare say about the amphibian mind. We have men- 

 tioned that frogs may learn the secret of a simple maze, and toads 



