SKATES. 81 



I give a fiG^iii-e as taken from the eye of tlie Common Skate. 

 It will be seen to possess a fimbriated border, and is coloured 

 within and without, although all besides within the chamber is 

 black. This curtain may be influenced by the appetites or pas- 

 sions of the creature, although it is not subject to the influence 

 of the will. It is too near the lens to be brought into its focus, 

 but it is the nature of a fringe like this to hinder the defi- 

 nition or formation of a border to the picture painted on the 

 visual nerve; thus producing an efifect similar to that caused by 

 an instrument lately invented by photographers, and placed by 



them in front of the object-glass or lens of the camera, to give 

 Avhat they term a vignette appearance to their pictures. An object 

 looked at by the fish becomes by this structure better defined, 

 because its attention is not permitted to be limited by any 

 margin that would appear from a border shaped by a more 

 simple iris. 



All able anatomist might not encounter insuperable difiiculty 

 in pointing out in the principal bones of the pectoral fins of 

 this class of fishes, what bears an analogy to the arm and 

 hand of a human being, of which that portion answering to 

 the thumb is extended forward to find support in a protube- 

 rance at the side of the head. From these bones proceed a 

 multitude of flexible and jointed rays, which constitute the 

 expansion of the pectoral fin, and at the same time provide 

 for its ireedom of action. These rays divide and sub-divide 

 as they are spread out, and in the Common Thornback Ray 

 amount to eighty two in number, having in them twenty rows 

 of joints; but I have seen them ossified, and thus made like 

 the bones of the classes termed osseous fishes, in which instance 

 their minute structure appeared beautifully radiated. 



It is the character of this family to have the ventral fins 

 arranged on a level with and as a continuation of the pecto- 

 VOL. I. N 



