THE EYES OF RHINEURA FLORIDANA 54I 



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

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

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



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



10. The eye of Rhineura does not represent a phylogenetically 

 primitive 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 ces- 

 sation of development at any definite ontogenic stage. It does not re- 

 semble 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 an- 

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

 the lack of union of the lips of the choroid fissure. 



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 that their absence in the adult eye of Rhineura is also due to 

 ontogenic degeneration. 



14. The irregularity in the structure and existence of the lens and 

 the great reduction of the vitreous body offer evidence in favor of the 

 idea of the ontogenically and phylogenically earlier disappearance of 

 the ontogenically and phylogenically newer structures. 



15. Horizontal nuclei found between the pigment epithelium and 

 the outer limiting membrane are probably derived from the proximal 

 layer of the optic cup. 



16. The different layers of the retina have reached a degree of dif- 

 ferentiation out of proportion to the great reduction of the dioptric 

 apparatus and general structure of the eye. 



ACKNOWLEDGMENTS. 



My attention was called to this lizard by Mr. W. S. Blatchley, State 



geologist of Indiana. Dr. W. B. Fletcher, of Indianapolis, kindly 



secured some specimens for me. To both of these gentlemen I wish 



to express my obligations. Other specimens were secured through 



dealers. 



BIBLIOGRAPHY. 



List of papers bearing on the eves of the Amphisba;nians. 

 Baur, George. 



1893 The Discovery of Miocene Amphisbaenians. Am. Nat., 1893, p. 998. 



1 The detailed considerations on which conclusions 10, 11, 12, 14 are based are 

 not presented in the body of this paper. They will, however, be granted no 

 doubt. 



