lOG 



The Eye of Rhineura Floridana. 



C. H. ElGENMANN. 



[Abstract.] 



RhLaeui-a floridana is a legless, burrowing, amphisbaenian lizai'd, found 

 in Florida. My attention was called to it by Mr. W. S. Blatchley, and I 

 secured specimens through dealers and through Dr. "W. B. Fletcher, of In- 

 dianapolis, who kindly forwarded a number of living specimens to me. 



A study of the eye of this lizard has led to the following conclusions: 



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

 a process of degeneration that pi'obably began in the early miocene. 



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

 tion. 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 was found. 



7. The vitreous body has practically disappeared. 



8. The pigment epithelium is variously pigmented. It is of greater 

 extent than is sufficient to cover the retina and lias been variously in- 

 vaginated or puckered over the proximal and posterior faces of the eye. 



9. An uveal part of the iris is not found. 



10. The eye of Rhineura does not represent a phylogenetically primi- 

 tive stage; it is an end product of evolution as truly as the most highly 

 developed eye. 



11. The adult eye shows few indications that there has been a cessa- 

 tion of development at any definite ontogenic stage. It does not resemble 

 as a whole any ontogenic stage. 



12. An arrest in the ontogenic development has taken place in so far 

 as the number of cell multiplications concerned in forming the anlage of 

 the various parts of the eye have decreased in number, and in the lack of 

 union of the lips of the choroid fissm-e. 



13. It is possible that the absence of cones or rods is due to an arrest 

 in the histogenesis of the retina, but since these structures are normally 

 formed in the young of Typhlotriton and disappear with age, it is possible 



