THE EYES OF THE BLIND VERTEBRATES OF NORTH AMERICA. 203 



Fig. 10. Transverse section of the right eye of the fish from which Figure 9 was taken. A large scleral carti- 

 lage is present. The pigment epithelium forms an elongated vesicle. The rest of the retina is an 

 irregular mass within the vesicle. A spherical lens-like body is seen at the right. 



Fig. 11. Horizontal section of the left eye of a Troglichthys showing its position relative to the brain. 



Fig. 12. An enlarged view of the same eye as that represented in Figure 11 showing the large scleral cartilages and 

 the different layers of the eye. 



PLATE XIII. 



Figures 13 to 20 were made from a series of embryos taken successively from one mother. Figure 22 

 (Plate XIV) begins another series. Later embryos and larvae were taken from different mothers. 

 Fig. 13. Outline of the head of an embryo between 1.3 and 1.5 mm. long. 

 Fig. 14. Outline of the brain and optic thickening in a mounted embryo 1.6 mm. long, with four protovertebrse 



(2.30 P.M., May 5). 

 Fig. 15. Outline of the brain and optic thickening in a living embryo 1.92 mm. long, with ten protovertebrae 



(9 P.M., May 5). 

 Fig. 16. Outline of the brain and optic vesicle of a living embryo 2.4 mm. long, with ten protovertebrse (12 P.M.; 



May 5). 

 Fig. 17. Outline of the brain and optic vesicle of a living embryo between the sizes of those shown in Figures 



16 and 18 (5.30 A.M., May 6). 

 Fig. 18. Outline of the brain and optic vesicle of a living embryo 2.4 mm. long, with twelve or thirteen proto- 



vertebrae (8 A.M., May 6). 

 Fig. 19. Horizontal section through the left eye of an embryo about 2.44 mm. long, two sections ventrad of the 



one represented in Figure 20. 



Fig. 20. Horizontal section through the head of the same individual showing the optic vesicle (11 A.M., May 6). 

 Fig. 21. Outline of the brain and optic vesicle of an embryo 1.68 mm. long, with five protovertebrse from a living 



specimen. 



PLATE XIV. 



Figs. 22, 23. Horizontal sections through the optic stalk (Fig. 22) and the optic vesicle (Fig. 23) of an embryo of the 

 second series. This embryo was 2 mm. long and in about the same stage of development as those 2.8 

 mm. long of the first series. 



Fig. 24. Horizontal section of the head of an embryo 2.5 mm. long, the two sides at different levels. 



Fig. 25. Left eye of the same embryo as that from which Figure 24 was taken, showing the first indication of the 

 lens. 



Fig. 26. Transverse section through the dorsal part of the optic stalk of an embryo 2.7 mm. long. 



Fig. 27. Optic vesicle and the beginning of the lens in another specimen 2.7 mm. long. 



Fig. 28. Transverse section of the optic vesicle and beginning of the eye of a Cymatogaster * larva, 1.5 mm. long. 



Fig. 29. Transverse section of the eye of a Cymatogaster larva 3.2 mm. long. 



Fig. 30. Transverse section of the eye of a Cymatogaster larva 4.5 mm. long. 



Fig. 31. Horizontal section of an Amblyopsis embryo 4.4 mm. long. 



Fig. 32. Section of the right eye of a larva 4.4 mm long. The nuclei were all drawn without a change of focus. 



Fig. 33. Vertical section of the eye of another larva 4.4 mm. long. 



PLATE XV. 



Figs. 34, 35. Two vertical sections of an eye of an individual about 5 mm. long. Fig. 34 is taken through the lens, 

 vitreous cavity, and choroid fissure. Fig. 35 is the second section proximal to that from which Fig. 34 

 was drawn and passes through the innermost part of the vitreous body. The layers of the retina have 

 not yet begun to be differentiated. 



* Cymatogastre is a teleost with large and'well developed eyes. Figures 28, 29 and 30 (Cymatogastre) should 

 be compared with Figures 27, 32, and 33 (Amblyopsis). j 



