3o6 Journal of Comparative Neurology and Psychology. 



fovea ' or other modified area of the retina. It seems the most 

 probable hypothesis that vision serves, as said before, for gen- 

 eral orientation, and for the organization of a situation in which 

 a stimulating odor forms one of the important elements. That 

 the one reinforces the other, and that both are utilized in ordi- 

 nary life processes is indicated by the comparison between re- 

 actions to a problem in ordinary daylight, and reactions to the 

 same problem in the dark where vision is practically useless. 

 The complete elimination of the food odor, and the employ- 

 ment of only a visual stimulus of food have thus far given nega- 

 tive results. 



//. Characteristics of the Developing Guinea Pig. 



A. Description of the Young Guinea Pig at Birth. 



As stated above, the guinea pig at birth is well covered 

 with hair, its eyes are open, it can hear, smell, touch and taste. 

 Movement is not coordinated, and slight muscular weakness is 

 apparent. Frequently when the little creature stops running 

 one hind leg is left sprawling behind the body. The head is 

 proportionally much larger than that of the adult. There is no 

 fear of an approaching object, such as the hand in front of the 

 eyes, nor of persons. But a shrill squeal like that of a rat causes 

 first an instantaneous jump, and then a twitching of the muscles. 

 This is a momentary reaction ; it may be followed by hiding 

 under the mother, but there seems to be no "panic." nor rapid- 

 ity of movement as if to escape. While this may be an initial 

 stage of fear, still the attitude of the little fellow is quite differ- 

 ent from that of the frightened adult. 



A carrot or other vegetable food produces no motor reac- 

 tion toward it, though before the first day is over the small 

 guinea pig will eat grass, bread and milk, and nibble at a carrot. 



Test I. Is the mother a specific stimulus for her young? 



Observation had indicated that carrot or other vegetable 

 food furnished no stimulus toward which the very young guinea 



' Preparations of the guinea pig's eye were kindly made and examined by 

 Dr. J. R. Slonaker, in this laboratory, and the above statement is made upon 

 his authority. 



I14] 



