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 Bovide and 
Cervide, 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 didactyli and pedes 
tetradactyli; but this character will not separate Antilocapride 
from Bovide, 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 family Antilocapride; 
for the genera Nesotragus and Nanotragus, 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 Bovide,” and proceeds, “in the 
absence of the ‘ false hoofs,’ as the stunted terminations of the 
ruaimental second and fifth digits of each foot are termed.” 
LIX.—On the Vision of Fishes and Amphibia. 
By Fruix Piatgau*. 
Tur 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, differmg 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 Mém. Cour. et Mém. des Savants Etrang. de l’Acad. Roy. 
de Bruxelles, tome xxxiii. Communicated by the Author. 
