CONCLUSIONS. 59 



CONCLUSIONS AS TO THE EYES OF BLIND REPTILES. 



AMPHISB^ENA. 



(1) The eye muscles have entirely disappeared. 



(2) Only the uveal parts of the iris remain. 



(3) The lens has retained its shape and position, but its structure has been 

 greatly changed. No capsule is present. 



(4) Harder's gland is many times larger than the eye and pours its secretion 

 into the conjunctival cavity and thence into the mouth. 



(5) The sclera, scleral cartilages, cornea, vitreous body, and pigment epithe- 

 lium have undergone but little change unless it be in the reduction in size. 



(6) The cuticle passes over the eye unchanged. 



(7) The aqueous cavity is no longer present. 



(8) All the layers of the retina are still present. As shown in figure 6, the 

 great reductions in the depth of the layers, in comparison with those of Anolis, have 

 taken place in the nerve fiber, ganglion cell, inner reticular and inner nuclear layers. 



(9) If the eye has been reduced from an eye of the average size, all parts have 

 certainly undergone considerable change, and this change has been approximately 

 equal among the several parts. 



(10) The retina does not show such a profound change as either the iris, muscles, 

 or lens. However, it has been greatly changed, as it extends only 50.7 per cent of 

 the distance around the eye. 



(u) The eye of Amphisbccna shows that the more active parts of the eye are 

 the ones to degenerate first. They are the parts which have been most affected. 



RHINEURA. 



(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 modifications. 

 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. 



(8) The pigment epithelium is variously pigmented. It is of greater extent 

 than is sufficient to cover the retina and has been variously invaginated 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. 



(n) The adult eye shows few indications that there has been a cessation of 

 development at any definite ontogenetic stage. It does not resemble as a whole 

 any ontogenetic stage. 



