THE TARPON 169 



THE EYE OF THE TARPON* 



The eyes of the deep sea fishes are of two quite different 

 types ; those with very large and well-protected eyes and those 

 in which the eyes are small, imperfectly developed or rudimen- 

 tary. The first go down to depths of one or two hundred 

 fathoms. The habitat of the second is in the abysmal deeps. 

 In the former the pupils are widely dilated, the lens is spheri- 

 cal and every structural arrangement is adapted to gather in 

 as many as possible of the light rays. Visible light is absorbed 

 by the water and it grows dimmer rapidly as it leaves the sur- 

 face until in the profounder depths, absolute darkness pre- 

 vails. Here many of the fishes are blind, others have electric or 

 phosphorescent organs which give some luminosity. Below two 

 hundred fathoms or thereabouts, the deep sea fishes that also 

 come to the surface cannot go, as the pressure of the water be- 

 comes enormous, being over a ton to the square inch for each 

 1,000 fathoms of depth. To sustain this pressure the entire 

 structure of the creature including that of the eyes has great 

 power of resistance. Below two hundred fathoms no animal 

 adapted to life in the upper levels could exist. 



The abysmal fishes are predacious. They do not resist the 

 great pressure in the profounder depths but are sponge-like in 

 form, the water passing through them. In their struggles with 

 other fishes, they are sometimes brought to the surface when 

 the gases expanding, tear the tissues to pieces. The eyes of 

 the pelagic fishes that swim in the deep waters have every 

 structural arrangement to adapt themselves to changing pres- 

 sure, soft fatty tissues in the orbit against which the eyes may 

 rest without being crushed and internal structures which allow 

 the passage of fluids from front to back. The eyeball is com- 

 pletely enveloped in the orbital tissues with the exception of 

 the cornea which is flat and clear. 



♦Dr. F. Park Lewis, of Buffalo, an eminent authority on the eye, has made a 

 scientific research into the eye of the tarpon, which I believe is the pioneer study 

 on this subject. I here set it forth with my thanks to the Doctor for his kindneas. 



