GENERAL REMARKS ON THE EYES OF FISHES. 63 



(Salmo, Coregonus, /), a single cone is found both at each angle and in the center 

 of the unit. The most complicated unit (Esox, g) is composed of 5 twins, 4 form- 

 ing the sides and i a diagonal, and of 4 single cones, i in each corner. These 

 patterns are all regular, but not mathematically so. 



In some families (Silurida- and Catostomidse) no regularity could be made out. 

 In general the number of rods is inversely proportional to the number of single cones. 



FIG. 23. i to 6 show Section of Eye of Bass 6 cm. long. The Eye measured 3.8 mm. in Diameter from 

 Cornea to Back, and 4.7 mm. from Anterior to Posterior Edges. 7, 8, and 9 show Sections of Eye of 

 Bass 33.5 cm. long. The Eye was 10 mm. in Diameter from Cornea to Back, and 13 mm. from 

 Anterior to Posterior Edges. All figures drawn to the same magnification. C, part turned toward 

 cornea; B, part pointing from cornea. 



In the black bass, the only species in which the pattern was examined over the 

 entire eye, the number of components in each unit of the mosaic is the same, but 

 the shape of the pattern varies regularly from a rectus at the anterior and posterior 

 faces of the eye, to a rhomb above and below. The elements of the unit and the 

 entire unit increase in size with the growth of the eye. New elements are not 

 added after the pattern has been established. 



