No. 3-] ACUTE VISION IN VERTEBRATES. 479 



less distinct. Vertical sections across this area show only a 

 slight increase in thickness, both on the nasal and temporal side 

 of the fovea (PL XXVIII, Figs. 32-34). 



Tame Duck (Anas boschas domesticus). 

 Surf Duck (Oidemia deglandi). 



Similar relations exist here as in the goose. The fovea is 

 quite shallow, and is surrounded by a distinct round area which 

 is situated on a band-like horizontal area (PI. XXVIII, Fig. 39). 



Ring-Neck Plover (^gialitis semipalmata). 



A very distinct band-like area is seen passing obliquely 

 through the retina. A dark line, resembling a trough-like 

 fovea, extends almost the full length through the center of this 

 area. Cross sections reveal, however, no trough-like fovea. 

 The single fovea nasalis, surrounded by a sharply bounded 

 round area, is observed located about the middle of the band- 

 like area. It is of medium depth and readily seen by the naked 

 eye (PL XXVII, Fig. 20, and PL XXIX, Fig. 47). 



Sparrow Hawk (Falco sparverius). 



• A fovea nasalis and a fovea temporalis, each surrounded by 

 a sharp round area connected by a short band-like area, are 

 easily observed. The fovea nasalis is very deep and sharp and 

 is situated about the center of the retina. The fovea tempo- 

 ralis, somewhat shallower, is situated near the ora serrata about 

 the same distance from the nerve entrance as the fovea nasalis, 

 but in a lower plane. The area temporalis is likewise smaller 

 than the area nasalis. The band-like area is not sharply 

 bounded, is of slight thickness, and extends only between the 

 two round areas. The fovea temporalis is similar in position 

 to that of the owl, and the fovea nasalis to that of the crow, 

 robin, etc. (PL XXVII, Fig. 19, and PL XXIX, Figs. 48, 49). 



Red-Tailed Buzzard (Buteo borealis). 



Almost the same conditions exist as found in the sparrow 

 hawk, excepting the two foveae are relatively nearer together 

 (PL XXVII, Fig. II, and PL XXIX, Figs. 50, 51). 



