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THE EYES OF THE BLIND VERTEBRATES OF NORTH AMERICA. 



EXPLANATION OF PLATES XII-XV. 



Unless otherwise stated the figures are from specimens of Amblyopsis spelaeus. The anterior end of a horizontal 

 section or the dorsal part of a cross-section or sagittal section is invariably toward the top of the plate. All the 

 drawings were made with the aid of the Abb6 camera and usually the 2-mm. apochromatic and the No. 4 or the 

 No. 6 compensating eyepieces of Zeiss. Credit for the photographs is given under the head of acknowledgments. 



ABBREVIATIONS. 



ami. Amyloid bodies of the pigment nl. con. 



epithelium. nl. gn. 



bac. Rod. nl. Muel. 



bac. + con. Rods and cones. oc. 



chd. Choroid. pro. nl. 



con. Cones. pupl. 



cpl. sng. Blood-corpuscles. r. 



crt. sd. Scleral cartilage. sb'orb. 



d. Dorsal aspect of eye. sd. 



e'th. pig. Pigment epithelium. st. gn. 



fis. chd. Choroidal fissure. 



jv. olf. Olfactory pit. 



hyl. Hyaloid membrane. st. nl. ex. 



ir. Iris. st. nl. ex. +in. 



ir.' Outer layer of iris. st. nl. in. 



ir." Inner layer of iris. st. opt. 



1. Left side of eye. st. ret. ex. 



Ins. Lens. st. ret. in. 



mu. Eye-muscle. 



n. opt. Optic nerve. v. 



nl. Nucleus. vit. 



nl.' Elongated nuclei of the pars 



ciliaris. 



Cone nuclei. 



Nuclei of ganglionic cell. 



Mullerian nuclei. 



Eye. 



Process of the cone nucleus. 



Pupil. 



Right side. 



Suborbital. 



Sclera. 



Ganglionic layer. The nuclei of this layer 

 are conventionally marked with a large 

 dot. 



Outer nuclear layer. 



Outer to inner nuclear layer. 



Inner nuclear layer. 



Optic fibre layer. 



Outer reticular layer. 



Inner reticular layer. This layer is con- 

 ventionally marked by dashes. 



Ventral aspect. 



Vitreous body. 



PLATE XII. 



Fig. 1. Larva at the time of hatching when it has a length of about 5 mm. 



Fig. 2. An older larva in the process of metamorphosis. The yolk is partly absorbed and the yolk-bag has 

 changed shape. The caudal, the dorsal, and the anal fins are developing. The tactile organs show 

 as prominent warts on the anterior half of the body and on the head. 



Fig. 3. Cross-section of the eye of a fish 75 mm. long. The most highly developed eye found. 



Fig. 4. Dorsal face of a horizontal section of the left eye of a fish 25 mm. long. The optic nerve is directed 

 forward and inward. 



Fig. 5. Horizontal section of the right eye of a young fish 9.5 mm. long. Compare with Figure 47 (PI. XV.) 



Fig. 5o. The same eye as that shown in Fig. 3 less highly magnified This figure is inverted in reference to Fig. 3. 



Fig. 6. Cross-section of the left eye of a fish 100 mm. long, showing the large scleral cartilage; the rest of the 

 eye is an irregular vesicle immediately below the cartilage. 



Fig. 7. Cross-section of the right eye of a fish 105 mm. long, showing the large vesicle formed by the pigment 

 epithelium and the rest of the retina as a small nodule on its distal face. 



Fig. 8. Anterior face of a transverse section of the left eye of a fish 123 mm. long. The scleral cartilage is at 

 the extreme left. The pigment epithelium forms an elongated vesicle with an invagination oppo- 

 site the scleral cartilage. The rest of the retinal elements form an irregular mass in the centre. 



Fig. 9. Transverse section of the left eye of a fish 130 mm. long. No definite structures are distinguishable 

 aside from the scleral cartilage. 



