ZOOLOGICAL SOCIETY BULLETIN 



RED HIND 



Note the pear sliaped pupil. The oute 



is pigmented above, transparent wl 



the cornea and pupil and becon 



less piffmenteci belo 



skin of the eyeball 

 re it passes over 

 s opaque and 



Tlie colored portion of the eye, the iris, is 

 usually yellow in color. However, one found 

 fish with the iris of different colors. In the 

 center appears the black part called the pupil, 

 usually round, as in man ; but, fish were found 

 whose pupils were pear-shaped, triangular, oval 

 and pointed at each end. The size of the pupil 

 does not appear to change very much on expos- 

 ure to a bright light or as rapidly as does the 

 pupil of most air-breathing animals. When the 

 light comes from behind the observer, the inte- 

 rior of the eyes of the fish show beautiful col- 

 ors ; shades of red, yellow, blue and green. 

 Many visitors at the Aquarium were entertained 

 for a long time by the wonderful variety and 

 kaleidoscopic changes of colors in the eyes of 

 the fish. Dr. C. H. Townsend has published 

 in one of the reports of the Zoological Society 

 a valuable and interesting paper on the changes 

 in the color of fish. 



Have Fish Good Eyesight? 



The men connected with the Aquarium have 

 told me some interesting stories of their won- 

 derful power of vision; and. one can believe 

 that fish do see well when tliey avoid obstruc- 

 tion in their ])aths while darting rapidly through 

 the water. 



The object of the study of fishes' eyes was to 

 find out the cause of near-sight and the need 

 of glasses acquired by school children. The 

 facts learned were of great practical value. One 

 theory of the cause of myopia or near-sight was 



that muscle inside the eye, called the ciliary 

 muscle, produced near sightedness. This theory 

 was not the truth in the case of fish, because 

 they have no ciliary muscle. Another theory 

 was that the near use of the eyes caused myopia 

 or near-sight. This theory did not apply to fish 

 because myopia or near-sight was not found in 

 fish like eels that habitually use their eye for 

 near objects. Near-sight or myopia was pro- 

 duced in fish by the action of two muscles out- 

 side of the eyeball, called the superior and in- 

 ferior oblique. They are so arranged about 

 the eyeball that they form a nearly complete 

 belt. \Mien these muscles contract, the belt is 

 tightened and consequently the eyeball is 

 squeezed out of its normal shape, just as one 

 would change the shape of a hollow rubber 

 ball by squeezing it when held in the hand. 

 The line or axis of vision becomes elongated. 

 The elongated eyeball like the photographic 

 camera with the bellows elongated is focussed 

 for near objects. 



With the aid of an instrument called the re- 

 tinoscope, which reflects the beam of an elec- 

 tric light into the pupils of the eyes of the fish, 

 it was determined positively that all the fish 

 examined while they were swimming in the 

 tanks, several hundred individuals of many spe- 

 cies, were neither near-sighted nor did they have 

 astigmatism. Their eyes were nearly normal 

 and were usually focussed accurately to see dis- 

 tant objects. The eyes of decapitated or dead 



Diauram — Red hind showing the transpal 

 ing: the front of the eye with a pro 

 the pear shaped pupil. 



