ZOOI.OGICAI. SOCIKTY BLI.LF.TIN 



YELLOW GRLNT 

 The pupii is nearly nniiui. 



FISHES' EYES. 



B;i W. H. Bates, -M.D. 

 (Photographs by Elwin R. Sanborn.) 



THE Aquarium is one of the show places 

 of New York. Here are gatliered sev- 

 eral thousand fishes so arranged that they 

 can be readily inspected while swimming in the 

 tanks. The crowds of people that visit the 

 place daily, testify to the fact that here is 

 something worth seeing. 



Some children were taken to the Aquarium 

 and were asked to tell what they saw of the 

 eyes of the fish. One boy eleven years old. said, 

 "the pike has an eyeball shaped like an egg 

 and their eyes seemed to be st;iring at you 

 when you looked at them." "The muskallunge 

 has eyes which go in and out; they are bright 

 with n yellow ring around them." The rainbow- 

 trout ajipearcd to him to have an eyeball sha]ied 

 something like a square, the eyes of the yellow 

 perch bulged at the top. He noted tin- tnr 

 quoise blue of the eye of the red hind. Hotii 

 he and his sister, aged seven, after two hours 

 did not want to leave. 



The eyes of the fish are in constant use ex- 

 ce]>t when they are aslee)). They move up. 

 down, to the right or left and rotate. In sonn; 

 fish these movements are quite marked. I'isli 

 liave large eyes relatively to man. The width 

 of the eyeball from side to side, is usually much 

 greater thaii its depth. A fish ten inches long 

 usuallv lias eyeballs about one-lialf of an inch 

 long, while a man seventy inches tall lias spher- 

 ical eyeballs about one inch long. One may 

 say that the eye of a fish is one-twentieth of 

 its length, while that of a man is occasionally 

 onlv one-sixtieth or one seventieth of his height. 



However, the black grouper has very large ej'es. 

 In one sjiecimen three feet long, the eyes were 

 nearly two inches wide. A nurse shark of abour 

 the same length had eyes less than one-quarter 

 of an inch wide. Eels four feet long had eyes 

 as small as those of the shark. 



My first impression of the fish seen in the 

 tanks of the New York Aquarium was that their 

 eyes seemed very open. Why? After investi- 

 gation it was found that most of them had no 

 eyelids. As tlieir eyes need protection, was 

 there anything else to save them from injurv? 

 .Most fish have their eyes protected by a slimy 

 material. The eyes of the red hind, yellow 

 grunt and others have a transparent skin over 

 the front part of their eyes, which is as thick 

 as the skin of the fish or as the eyelids of some 

 animals which live on the land. In the herring, 

 this transparent skin covers only a part of the 

 eye. Exposure to the air was soon followed by 

 a cloudiness of the transparent coat of the eye 

 so that in a few minutes, or less, the interior 

 of the eye could not be seen with an instrument 

 called the opthalmoscope. The puffer, or swell 

 fish, living in salt water, has eyelids which cover 

 the eyeball when closed. The lower eyelid is 

 much larger than the iijiper. being the reverse 

 of the condition found in man, whose upper lid 

 is larger than the lower. 



Mr. L. L. Mowbray, of the Aquarium staff, 

 suggested that the puffer needed eyelids for 

 the protection of its eyes because of its habit 

 of burrowing in the sand at the bottom of the 

 water. 



YKLLOW URIXT 



ileatal cvehall held by forcep.*, The 



covering the front of the eyeball has 



not been remnvcil. 



