THE EYES OF RHINEURA FLORIDANA 



537 



beyond the eye, stain a different tint and readily become separated, 

 they are easily distinguishable. They probably represent the sclera 

 and choroid. If so the choroid is practically free from pigment ex- 

 cept possibly in rare instances where a few pigment granules were 

 detected in cells closely applied to the eye. There is no indication of 

 any differentiation into a cornea or capsule of any sort. The fibrous 

 sheaths are at the proximal end drawn out into a cone. A supposed 

 scleral cartilage has been found in one individual. Here a bar about 

 20 /x thick extends from over the center of the distal face of the eye 

 for 160 /J. around its posterior face. It stains and has the structure of 

 bone rather than of cartilage. 



No traces of any muscles have been found connected with the 

 eye. 



The eye is directed outward and forward. Its axis is horizontal and 

 makes an angle of about 60° with the sagittal plane of the body. It 

 does not occupy a definitely fixed position on its axis. In the eye of 

 one side the choroid fissure was found directed caudad, in the other 

 eye ventrad. It is irregularly pear-shaped, with its anterior face con- 

 vex, its posterior face flat or even concave. The eyes in three speci- 

 mens give the following measurements in microns : 



MEASUREMENTS IN MICRONS OF EYES OF RHINEURA. 



MINUTE ANATOMY OF THE EYE. 



All the structures vary greatly in different eyes so that the terms 

 "sometimes," "usually," frequently," etc., have to be used much 

 more than is desirable. This cannot be avoided unless each eye is 

 given a distinct description. 



(a) The Iris. — In the structure of the irideal region the eye of this 

 species is unique among the degenerate vertebrate eyes so far described. 

 In all other eyes, with the possible exception of Troglichthys., elements 

 of an iris are distinctly recognizable. In Rhineura the fold of double 

 epithelium between the pigmented and unpigmented part of the retina 

 whose margin is the margin of the pupil has been obliterated and the 

 pupillary edge forms the extreme outer edge of the blunt end of the 

 pear (PI. xxxiii, fig. i, /). The pigmented layer of the retina in 



