XXXU THE EYE. 



In inost teleostean or bony fishes, and likewise in the sturgeon or 

 Acirpenser, a fibrous ligament attaches the sclerotic to the walls of the orbit. 

 As a rule the external muscles of the eyeball are similar to what exist among 

 the higher vertebrates, consisting of four straight and two oblique pairs. . 



Fishes eyes present a great variety as well as extent of outer coverings, 

 some portions of which are transparent while others are opaque. Skin, in 

 accordance with where it is situated, may have different offices to fulfil, for 

 which purpose it may be necessary to be either opaque or transparent, thick 

 or of a very thin structure, and that which covers the eyes of fishes may be' in a 

 single or double layer, either or both of which maybe extensively modified. 

 The skin which covers the eye is commonly thin in substance and transparent in 

 character, being modified in order to suit altered conditions as it passes across 

 and covers the front of the ball of the eye, and its glass window known as 

 the cornea, through which all rays of light must necessarily pass to obtain 

 access through the pupil to the retina. This skin is essentially a continuation 

 of that which covers the contiguous parts of the head being reflected from 

 off the walls of the orbit on to the front of the eye, where it is more or less 

 firmly adherent to the cornea. But as it is necessary for the ball of the eye 

 to be capable of being turned in various directions it is obvious that some 

 means must be found to prevent the skin arresting its movements, which it 

 would do were it to pass by the shortest cut from the bony orbital walls 

 to the front of the eye to be there adherent to its surface. This is provided 

 for by its being loose as it passes this gap on to the eye, and being so it does 

 not impede any movements of the globe. This loose or baggy portion which 

 surrounds the eye from the orbital edge to that of the transparent cornea is 

 the portion which after death appears white and opaque, for it is modified 

 skin that takes on this appearance, and often due to its being sodden. The 

 foregoing descriptions briefly refer to such forms as we commonly meet with, 

 and which possess but a single layer of skin across the front of the globe of 

 eye, but in this skin during life no sufficient amount of colouring matter 

 exists to occasion opacity, neither are scales present. 



In the next class of fishes to which I shall refer, there still exists but a 

 single layer of skin passing across the front of the globe of the eye, but 

 this is modified, as shown in the mackerel, 8comber scomber, wherein what 

 have been termed " adipose lids " are present on either side of the eye, and 

 covering a portion of its ball. If these adipose lids are examined it is found 

 that the one which covers the anterior portion of the eye is attached 

 inferiorly to or is a continuation of the skin on the front of the preorbital bone, 

 and is consequently situated anterior to or overlapping the base of the 

 posterior lid, which is attached to the posterior edge of the preorbital. The 

 use of this will be readily understood, because in this manner any current 

 of water would pass backwards over a smooth surface, which would not be 



