4O EIGENMANN AND DENNY. [VOL. II. 



the larva with a proportionally thicker ganglionic layer than in 

 the related epigaean forms. Marked ontogenic degenerations 

 take place during and shortly after the metamorphosis, a. The 

 outer reticular layer disappears, b. The rods and cones lose 

 their complexity of structure, such as differentiation into inner 

 and outer segments, and finally are lost altogether. 



EXPLANATION OF FIGURES. 



All drawings were made with the aid of the Abbe camera from sectioned 

 balsam preparations. The comparative measurements (p. 39) furnish the key 

 to the magnification : 



ps. palpabra superior. pi. palpabra inferior, 



i. pigment epithelium. 2. rods and cones. 



3. outer nuclear layer. 4. outer reticular layer. 



5. horizontal cell layer. 6. inner nuclear layer. 



7. spongioblastic layer. 8. inner reticular layer. 



9. ganglionic layer. 10. optic fibers. 



FIG. i. Diagrammatic representation of the eye drawn to scale. 



FIG. i, a. Vertical section through the cornea and lids of an adult. 



FIG. 2. Section of the retina, exclusive of pigment cells, of a larva 35 mm. 

 long. 



FIG. 2, a. Tangential section through the rods and cones about on a level 

 with the innermost extent of the pigment which is seen on the right, showing 

 the relative sizes and abundance of the rods and cones. 



FIG. 3. Section of the retina of a larva 48 mm. long. 



FIG. 4. Section of the retina of a larva 90 mm. long. 



FIG. 4, a. Tangential section showing the rods and cones at about the inner 

 limit of the pigment which is seen on the left. 



FIG. 5. Section of the retina of an adult 106 mm. long. 



FIG. 5, a. Tangential section at about the inner limit of the pigment. 



FIG. 6. The only cone found in the eyes of adults. 



FIG. 7, 8. Difference in the shape of the outermost series of cells in the 

 outer nuclear layer. 



FIG. 9. Section of the retina of an adult 97 mm. long. 



