540 EIGENMANN 



3. The outer nuclear layer consists of about two series of elliptical 

 nuclei. They form a compact and distinct layer a few microns from 

 the outer limiting membrane (PL xxxii, fig. 5 ; PI. xxxiii, figs. 1,2; 

 PI. XXXIV, fig. 4). 



4. The outer reticular layer is represented by a series of distinct but 

 irregular gaps between the outer nuclei and the inner nuclei. Hori- 

 zontal cells are not present (PL xxxii, fig. 5 ; PL xxxiii, figs, i, 2, 3). 



6. The inner nuclei are smaller, rounded and less granular than the 

 outer nuclei. They do not form as compact a layer as the outer nuclei. 

 It is impossible to distinguish between bipolar and spongioblastic cells 

 (6 in the different figures) . 



8. As is usual with the inner reticular layers in degenerate eyes this 

 layer is well developed in the eyes of Rhineiira. It is frequently 

 crossed by Miillerian fibers (8 in the figures). 



9. The ganglionic layer is represented by a number of nuclei loosely 

 grouped about the vitreous slit. The individual nuclei are distinctly 

 larger than those of the inner nuclear layer and less oval than those of 

 the outer nuclear layer (9 in the figures) . 



10. A distinct optic fiber layer is not present and the optic nerve is 

 nowhere within the eye a compact strand of fibers. A loose flocculent 

 strand of fibers passes through the proximal part of the retina. Its 

 path through the pigmented layer is difficult to trace. Beyond the eye 

 the optic nerve can be followed in my preparations by means of the 

 fibrous sheaths and pigment cells associated with it (PL xxxiii, fig. 4) 

 rather than by the presence of any fibers with a distinctly nervous 

 structure. The optic nerve leaves the eye not at the proximal end or 

 the narrow end of the pear but anterior to the pigment mass in the 

 narrow part of the pear (PL xxxiii, fig. 2, n. op.'). 



CONCLUSIONS. 



1 . The eye of Rhineura has reached its present stage as the result 

 of a process of degeneration that probably began in the early Miocene. 



2. The dermis and epidermis pass over the eye without any modifi- 

 cations. The conjunctival pocket has vanished. 



3. Harder's gland is many times as large as the eye and pours its 

 secretion into the tear duct and thus into the nasal cavity. 



4. The eye muscles have disappeared. 



5. A cornea is not differentiated. 



6. The lens is absent in half the eyes examined and varies greatly 

 in those in which it is present. 



7. The vitreous body has practically disappeared. 



