On the Structure of the Iris of the Eye of Fishes. 181 



tempting objects, even at the distance of fourteen feet or 

 nearer, no motion of the iris was perceptible ; nor was there 

 any change when the fish has been removed from the water 

 into bright sunshine. The living young of the picked dogfish 

 have also been taken from the body of the parent and exposed 

 to the glare of a bright sunshine without any sensible effect on 

 the iris ; and when several examples of different kinds of fishes 

 were examined, in order to ascertain whether some difference 

 in the extent of this organ might be discerned in one or other 

 of the several species, the result was that nothing further could 

 be detected than might be looked for in the difference of size 

 or other particulars of the same sort. But the result of our 

 inquiry was somewhat different when the inquiry was extended 

 to the species of the sharks and. rays. But first, in the flat 

 fishes, or Pleuronectidce, the line of vision is not directed 

 upward, as is often represented in the stuffed examples of 

 museums and in many engravings ; but the eyes are raised 

 above the surface, and directed laterally, so that vision is pro- 

 tected from the glare of too much light, and the upper portion 

 of the iris is so far bent downward as sometimes to serve the 

 purpose of a partial screen ; but still without the power of 

 motion or contraction ; while in the depressed section of car- 

 tilaginous fishes, or the rays and skates, this upper portion of 

 the iris not only receives a new shape, but it is endued with a 

 new property, which has an influence on the further modi- 

 fication of the eye itself, or the particular function of sight. 

 The curtain, or veil, which hangs down from the upper portion 

 of the iris is, in fact, a covering- to the superior border of the 

 pupil, for which it serves a use that has been particularly 

 pointed out in our History of the Fishes of the British 

 Islands ; but it is to a peculiar structure of this portion of the 

 eye in these fishes that I wish to direct particular attention. 

 On attentive examination of this portion of the iris of these 

 fishes, it is seen that on the anterior portion the surface is 

 smooth, and not, as in birds, striated and irregular ; but in its 

 substance the texture is loose, and viewed under a microscope 

 it appears to be composed of an exceedingly fine, but irregular 

 network, which is not composed solely of vessels, but is more 

 loose about the middle distance between the pupil, or inner 

 border of the iris, and its outer circumference ; and it becomes 

 more condensed as it approaches the pupil in one direction 

 and the circumference on the other. At what may be termed 

 the border of the pupil there is a condensed rim of the same 

 texture, so that the iris itself has a finely granular appear- 

 ance, and the condensation is directed along even the border 

 of the fringes of the dependent curtain ; which portion of the 

 iris, if we may judge from the difference of appearance it 



