CAVE FISHES OF NORTH AMEKICA. 385 



Doctor Eigenmann has worked out the following key to the Ambij"- 

 opsida?, based on the structure of the e3'e:" 



a. Vitreous body and lens normal, the eye functional; no scleral cartilages; eye per- 

 manently connected with the brain by the optic nerve; eye muscles 

 normal; no optic fiber layer; minimum diameter of the eye 

 700 f.1 CJiohgaster. 



b. Eye in adult more than 1 mm. in longitudinal diameter; lens over 0.5 mm. in 

 diameter; retina very simple, its maximum thickness 83.5 jit in the 

 old; the outer and inner nuclear layers consisting of a single series 

 of cells each; the ganglion layer of isolated cells; maximum thick- 

 ness of the outer nuclear layer 5 jn, the inner layer 8 n .cornnins. 



bb. Eye in adult less than 1 mm. in longitudinal diameter; lens less than 0.4 mm.; 



outer nuclear layer composed of at least two layers of cells; the 



inner nuclear layer of at least three layers of cells, the former at least 



10 u thick, the latter at least 18 u. 



e. Pigment epithelium 65 mm. thick in the middle aged, 102 in the 



old papiUiferus. 



cc. Pigment 49 /.i thick in the middle aged, 74 in the old; 24 to 30 per cent 



thinner than in papilliforus; eye smaller agassizii. 



aa. The eye a vestige, not functional; vitreous Ijody and lens mere vestiges; the 

 eye collapsed, the inner faces of the retina in contact; maximum 

 diameter of the eye about 200 jit. 

 d. No scleral cartilages; no pigment in the pigment epithelium; a minute 

 vitreal cavity; hyaloid membrane with blood vessels; pujnl not 

 closed; outer nuclear, outer reticular, inner nuclear, inner reticular, 

 ganglionic, and pigment epithelium layers differentiated; cones 

 probably none; no eye muscles; maximum diameter of the eye 

 180 ji; eye probably connected with the brain throughout 



life Typhlichthys. 



dd. Scleral cartilages present; pigment in the pigment epithelium; vitreal 

 cavity obliterated; no hyaloid membrane; pupil closed; some of 

 the eye muscles developed; no outer reticular layer; jnner and 

 outer nuclear layers merged into one; eye in the adult not conxiected 

 with the brain. 

 e. Pigment epithelium well developed; cones well developed; gangl-'onic 

 cells forming a funnel-shaped mass through the center of the eye; 

 pigment epithelium over the front of the eye without pigment; 



maximum diameter of the eye about 200 ji Amblynpsis. 



ee. Pigment epithelium developed on the distal face of the eye, rarely 

 over the sides and back; no cones; nuclear layer mere vestiges; the 

 ganglionic layers restricted to the anterior face of the eye just 

 within the pigment epithelium; maximum diameter of the eye 

 about 85 jt TrogUchthys. 



CHOLOGASTER Agassiz. 



Chologuster Agassi'/j, Amer. Jour. Sci. and Arts, XVI, 1853, 135 {corniitus). 



The genus Chologaster is distinguished from the other genera of the 

 Amhlyopsldx by the presence of well-developed ej^es, which vary 

 greatly in the different species of the genus. All of the species pos- 



« Eigenmann, Eyes of the Blind Vertebrates of North America, Archiv fiir 

 Entwickelungsmechanik der Organismen, VIII, 1899, 607. 



F. C. 1904—25 



