PHYLOGENY OF COLOR VISION 



an original chondrostean color-vision system, and may have passed it 

 on to the reptiles and, through them, to the birds on the one hand and 

 the mammals on the other (Fig. 156). If so, the modern amphibians 

 lack color vision because they have discarded it as something useless in 

 their mode of life. Since no living color-seeing forms bridge the gap 



[Higher P l acentals| 

 |Pnmates) lMC:z::;^ ' I 



[insec ti voresi 



COLOFf VISION: 



PresenI | 



Probably present — 

 Possibly present — [^ 



— D 



Absent - 



Fig. 156 — The probable phylogeny of color vision in vertebrates. 



between the turtles and the fishes, we probably have no right to suppose 

 that the sauropsidan and teleostean color-vision mechanisms represent 

 only one single invention of long duration and wide distribution — at 

 least, not until the holosteans are shown to discriminate hues. Unfortu- 

 nately, no diurnal chondrosteans are left on earth. 



