EYES AND SCALES OF FISHES. 385 



Since these observations were originally made by me on the 

 spicula of the eye, I have been led to extend my inquiries to 

 other parts of the fish ; and though I have not yet had time to 

 vary my observations as fully and widely as with more leisure 

 I would have done, I may state even now, that I have ascer- 

 tained beyond a doubt, that the brilliant colours of the surface 

 of this splendid tribe of animals are not owing, as Cuvier sup- 

 poses, to a mucous * substance, but to bodies in every respect 

 the same as the spicula of the choroid coat of the eye. The 

 scales of fishes are pellucid ; and their brilliant appearance is 

 owing to a thin film, which covers the underside of each scale, 

 and is itself entirely formed of spicula, as is easily proved by 

 scraping off a quantity of scales, and agitating them in water 

 with a stick or other body, so as to detach the films. The wa- 

 ter will then be found to contain thousands of moving spicula, 

 which, in the sunshine, may be discerned with the utmost ease 

 by the naked eye. The scales of the salmon answer best for 

 this purpose, as they are large and easily detached. 



* " Of all vertebral animals," says this illustrious physiologist, " fishes are 

 the most remarkable for the brilliant and metallic colours which their rete muco- 

 sum exhibits. We find in them gold, silver, and copper, tin, lead, and even all 

 the tints which these metals assume in different degrees of oxydation. But as 

 the description of these colours is the province of Natural History, properly so 

 called, we wish merely to point out in this place, that they are produced by the 

 mucous substance which adheres closely to the internal surface of the scales, and s 

 with which it is frequently renewed." Sect. xiy. 



