678 



THE EYE IN EVOLUTION 



Lamprey 



Fig. 814. — The Experimental Measurement of the Visual Field. 

 A light is moved along the arc of a perimeter and the image is seen 

 trans- sclerally behind the globe. The dissected head of the animal (a bird) 

 is clamped centially. T. temporal, C, central fovea (Rochon-Duvigneaud). 



The binocular field of cyclostomes is small, but with an angle 

 of 160° between its optic axes the lamprey should have an effective 

 although minute binocular field some distance in front of its head. 



The binocular field of fishes is generally relatively small and is 

 represented both in the horizontal and vertical planes. In the usual 

 type of fish with laterally directed eyes and a cigar-shaped body the 

 binocular field is confined to a relatively narrow belt widest in front, 



Fig. 815. — The Binocular Visual Field of a Torpedo-shaped Fish 

 WITH Laterally Directed Eyes. 



