THE MAMMALIAN EYE 251 



Hypermetropic animals, and probably all animals are hyper- 

 metropic in the wild state, may well fail to discriminate form 

 at short range. The same criticism would apply in a lesser way 

 to discriminations of brightness and color, especially where the 

 differences are slight. 



Mr. Watson's rats 5 and Miss Allen's guinea pigs 6 failed to 

 discriminate food at sight and experiments with the dancing 

 mouse by Mr. Yerkes 7 for discrimination of form gave nega- 

 tive results, but Messers. Thorndike 8 and Kinnaman 9 ob- 

 tained discrimination of form from monkeys and Porter 10 

 and Rouse " from sparrows, cow-birds and pigeons. The mon- 

 key's eye anatomically is very similar to that of man and birds 

 possess a well defined fovea, sensitive area and a retina with 

 both rods and cones. A fovea is most likely essential to form 

 discrimination although in discussing the lack of such power, 

 as has been said, we may have to face the charge of providing 

 forms for discrimination which are entirely strange to the ani- 

 mal's life and habitual discriminations if it makes any. 



These studies seemed to confirm the general belief that the 

 vision of these animals was not of the strongest, still we were 

 not shown where the weakness lay. The following tabulation 

 is the result of a search for such anatomical, physiological 

 material and gives in this form, so far as found, the answer 

 sought. The facts are compiled chiefly from the work of Chie- 

 vitz, 12 Lindsay Johnson, 13 Slonaker, 14 and Harris. 13 



Dr. Johnson not only examined the eyes of the animals with 



5 Watson, J. B. Animal Education 1903, p. 58. 



6 Allen, Jessie. Association in the Guinea Pig. Jour, of Comp. Neur. and Psych., 

 1904, Vol. 14. 



7 Yerkes, R. M. Op. tit., p. 180. 



8 Thorndike, E. L. p Imitation in Monkeys. Amer. Jour, of Psych., 1902, Vol. 

 13, p. 98. Animal Intelligence, New York, 1911. 



9 Kinnaman, A. J. Mental Life of two Macacus Monkeys in Captivity. Amer. 

 Jour. Psych., 1902, Vol. 13, p. 98. 



10 Porter, J. P. The English Sparrow and Other Birds. Amer. Jour. Psych., 

 1906, Vol. 17, p. 264. 



11 Rouse, J. E. The Mental Life of the Domestic Pigeon. Harvard Psychological 

 Studies, 1906, Vol. 11, p. 581. 



12 Chievitz, J. H. Ueber das Vorkommen der Area Centralis Retinae. Arch, 

 f. Anat. u. Physiol, Anat. Abtlg., 1891, p. 311. 



13 Johnson, G. L. Contributions to the Comparative Anatomy of the Mammalian 

 Eye. Phil. Trans. Roy. Soc, 1901, Vol. 194 (B), pp. 1-82. 



14 Slonaker, J. P. A Comparative Study of the Area of Acute Vision. Jour, 

 of Morph., 1897, Vol. 13, pp. 445-494. 



15 Harris, W. H. Binocular and Stereoscopic Vision. Brain, 1904, Vol. 27, p. 106. 



