M. F. Plateau on the Vision of Fishes and Amphibia. 469 



genus under consideration ; and if it differs in two genera so 

 nearly allied as Tragulus and Moschus, which many modern 

 zoologists consider only species of one genus_, what right have 

 we to assume that it is similar in all the genera of Bovidce and 

 Cervidce, more especially as the placenta of very few species of 

 the large group of Antelopes and Deer is known. 



Dr. Sclater proposes to divide the Ruminantia unguligrada 

 with placenta polycotyledonaria into pedes didacUjli and pedes 

 tetradactyli; but this character will not separate ^w/i/ocflpnc?« 

 from Bovidce, unless he proposes to arrange several animals 

 which have been called Antelopes, and which have simple horns 

 with a permanent horny sheath, and which therefore do not agree 

 with his other characters of the group, in the iamily Antilocapridcs; 

 for the genera Nesotragus and Nanoti'agus, and one species of 

 the genus Calotragus are as destitute of false hoofs as the genus 

 Antilocapra. Dr. Sundevall considers the absence of this false 

 hoof of so little importance that he places two species in the 

 genus Calotragus, one having large and the other being en- 

 tirely without false hoofs. Dr. Sclater must have overlooked 

 this fact when he says, "two other points in which the Prong- 

 horn differs from all the other Bovidce," and proceeds, "in the 

 absence of the ' false hoofs,' as the stunted terminations of the 

 rudimental second and fifth digits of each foot are termed." 



LIX. — On the Vision of Fishes and Amphibia. 

 By Felix Plateau*. 



The eyes of animals have formed the subject of a great number 

 of investigations, which, however, have been almost always di- 

 rected to a purely anatomical end. In studying the physiology 

 of vision, observers have, so to speak, confined themselves to man, 

 and the question of the vision of animals, interesting as it is, 

 has only been lightly touched upon ; moreover physiologists 

 have generally proceeded by analogy, very rarely supported by 

 experiment. There are especially two groups of living creatures 

 which, differing so much in their habits from man, merited in- 

 vestigation from the point of view of their vision, namely the 

 Fishes and Amphibia; and it is these which I determined 

 specially to examine. 



In order to show to what kind of investigations and experi- 

 ments I have subjected the eye of these animals, let us conceive 

 for a moment an ideal typical eye of a fish. Its cornea will be 

 perfectly flat, its crystalline spherical, and the aqueous and 



* From the Mem. Coiir. et Mem. des Savants Etrang. de I' Acad. Ro3\ 

 de Bruxelles, tome xxxiii. Communicated by the Author. 



