No. 3-] ACUTE VISION IN VERTEBRATES. 475 



cernible. This I have called the area centralis. It is situated 

 near the center of the retina, but slightly above and toward 

 the temporal side. The nerve entrance is very noticeable and 

 of unusual shape. The nerve is flattened out fan-like just 

 before piercing the sclerotic, so that the papilla is narrow and 

 elongated. PI. XXVII, Fig. 14, represents the entrance of 

 nerve and the position of the area as nearly as I can ascertain 

 it in Sciurus niger. 



Bat ( Vesper tilio subulatus). 



I have not been able with the material at hand to demonstrate 

 an area. 



Sheep (Ovis avies). 



Chievitz (31, b) has described this area as not visible to the 

 naked eye, round, about 4 mm. in diameter, and located about 

 8 mm. toward the temporal side of the nerve entrance. I have 

 examined more than 20 eyes, and in every case find a white, 

 band-like region, about 1-2 mm. broad, extending horizontally 

 across the retina, gradually becoming invisible to the naked 

 eye just before reaching the ora serrata. It compares favorably 

 in every respect with the area centralis of the cow. It lies 

 above the nerve entrance, which is below the center and toward 

 the temporal side. PI. XXVII, Fig. 8, represents the position 

 and extent of the area and its relation to the blood-vessels and 

 nerve entrance in the left eye. 



Cow (Bos taurus domesticus). 



A horizontal band-like area 1-2 mm. broad is present, hav- 

 ing the same general relation to the nerve entrance and blood- 

 vessels as found in the sheep (PL XXVII, Fig. 6). 



Pig (Sus domesticus). 



A band-like area about i mm. broad passes horizontally across 

 the retina, and has the same relation to the blood-vessels and 

 nerve as that described for the sheep and cow. The nerve 

 entrance is nearer the center of the retina (PI. XXVII, 

 Fig. 9)- • 



