CONSIDERATIONS ON SIGHT IN BIRDS LEWIS. 345 



that the retina is not stimulated by wave lengths as short as that of 

 the violet, while yet possessing the whole of the range of colors as 

 far as the violet. In man we know that the eye is blind beyond the 

 two limits of red and violet, but we are able to ascertain the presence 

 of ultra red and ultra violet rays that the retina does not register. 



There is still a great field for investigation into the function of 

 sight. So far the Avork done is mainly comparative, and must be 

 based on the lines found existent in the human subject, where the 

 subjective assistance is of great value. But of the conditions in birds 

 we can only theorize, while there may be present conditions outside 

 our comprehension of the powers of the eye. There is still much 

 to be learned concerning accommodation, monocular vision, color 

 vision, and the function of the pecten. 



