598 KARL T. WAUGH 



A search through the sections of the eye failed to reveal struc- 

 tural signs of a fovea in any part of the eye. There was to be 

 found no point in which the inner layers of the retina are sacrificed 

 for the benefit of the rod layer, nor was there discovered a differ- 

 entiation of the rods in any particular region. 



V. SUMMARY 



We may now bring together for convenience of reference the 

 conclusions that have been drawn from the several researches: 



1. The mouse distinguishes differences in grays and in bright- 

 ness of lights with a considerable degree of accuracy. The dis- 

 crimination of the albino mouse is not so good as that of the mouse 

 with pigmented eyes. Illumination of the environment is influen- 

 tial in determining choice of light or dark objects. Black and white 

 are preferred to grays. 



2. Red and blue objects, which appear of the same intensity 

 to the human eye, are discriminated between by the black mice, 

 the percentage of error being less than in the case of the grays. 

 Red and yellow are preferred to blue and green. 



3. Albino mice do not show any discrimination between red 

 and white lights. With black mice a very bright red and a white 

 of low intensity are distinguished with greater difficulty than 

 colors which are to the human eye of equal brightness. Discrimi- 

 nation between green and blue light is not apparent. 



4. Perception of form is very poorly developed. The eye does 

 not seem to be suited to any distinct perception of outlines. 



5. The distanceof objects is perceived within a range of 15 cm. 



6. The mice fail to profit by estimating the depth of objects. 

 The black mice make more errors in this respect than the albinos. 



7. Our anatomical investigation shows mice to be lacking in 

 retinal cones, confirming what has been surmised by Allen and by 

 Morgan, and stated by Slonaker. We do not think it follows, as 

 Morgan would suggest, that the absence of cones in mice, bats, 

 hedgehogs and such nocturnal animals implies inability to distin- 

 guish colors. It is quite possible that the rods in the mouse are 



