172 



THE TARPON 



The tarpon's cornea is thinner in the center, grows thicker 

 at the pupillary margin, and thins again as it joins the sclerotic 

 coat. 



Between this thickened point and the margin the iris is 

 closely applied to the cornea except at the pupillary margin 

 where it is free. The bony tissue continues for 20 m.m. back 

 when the sclera becomes a thick firm membrane. It changes 

 also in color from shiny black to ivory yellow. The globe 

 would be spheroidal were it not for an added hemisphere 

 occupying the inner side, the diameter of the greater sphere 

 being 40 m.m., that of the smaller, 20 m.m. 



The iris of the tarpon with the pupil normal size. In the low- 

 er inner portion will he seen a small circular opening in which 

 the outer membrane is lacking. At its margin a valve-like open- 

 ing is found. 



The iris is of a golden yellow hue and is closely applied to 

 the thickened margin of the cornea including a space 3 m.m. 

 in extent on the attached side, 1 m.m. on the pupillary margin 

 side being free. The broad iris surrounding the pupil has a 

 silvery sheen. 



