lIAntS, FEATHKKS, AND SCALES. 



23 



BOALE OP FIOCNDEE. 



a. J^atural size. 



from the Flounder, which, being coarsely lined, shows 

 the structure well ; or in these from the Green "Wrasse. 

 I will now apply to one of these a power of 600 di- 

 ameters, concentrating the 

 light thrown through the 

 scale from the mirror by 

 the achromatic condenser, 

 and examine the scale 

 anew. You now see two 

 distinct layers ; the upper 

 one which bears the con- 

 centric lines, and a lower 

 clear one which not only 

 fills the radiating bands, 

 but underlies the whole of the lined parts. The con- 

 centric lines of the upper layer do not now appear to be 

 edges of successive plates, but irregular canals running 

 through the solid substance. This, however, is illusory : 

 . for, by delicate focussing, we perceive that each portion 

 marked by these lines is really in a difierent plane from 

 the others, tliat the highest is at the centre of radiation 

 of the scale, and that each is successively lower till we 

 reach the margin. But now, if with very sharp scissors 

 we cut one of these scales longitudinally through the 

 centre, and examine the cut edge, we find that each of 

 these lines forms a distinct ridge. On the other hand, 

 the under layer of clear substance is quite smooth, and 

 always a little exceeds the margin of the concentrically 

 lined portion. The clear substance that fills the radiat- 

 ing slits agrees both in texture and level with this lower 

 layer, and is manifestly continuous with it. 



Hence, I think that, in these slit scales, the upper 

 layer is formed, as commonly believed, by successive 



