Prof. Reid on the Vogmaiais Islandicus. 471 



tiiiated together as those on the skin. I did not succeed in 

 making any accurate measurements of these, but some of them 

 were about 3^0^00^^ ^^ ^° vi^ch in breadth, the greater number 

 however, were narrower than this, and the longest about j^oth of 

 an inch in length. They dissolve in aqua potassse, and when sub- 

 jected to the action of diluted muriatic acid under the microscope 

 no bullae of gas were evolved, indicating that they are composed of 

 animal membrane. When detached they do not exhibit any me- 

 tallic lustre when examined by transmitted light, but do so when 

 examined by reflected light. Sir David Brewster had the kind- 

 ness to give me the following repox't upon the optical properties 

 of these fibres : — " Having had occasion to examine by the mi- 

 croscope the colouring matter of different fishes, I was surprised 

 to observe that the colouring matter of the Vaagmaer which you 

 were so good as to send me presented phsenomena different from 

 what I had seen before. When removed from the skin and se- 

 parated from the membrane with which it is connected, it was 

 resolved into a great number of short and minute prisms, whose 

 length was about six or eight times their breadth. These prisms 

 had regular axes of double refraction, and absolutely disappeared 

 under the polarizing microscope when the plane of primitive 

 polarization was either parallel or perpendicular to the axis of the 

 prism. The phsenomena which these prisms exhibited were quite 

 different from those shown by animal and vegetable fibres which 

 have a doubly refracting structure. I am disposed to think that 

 the prisms are analogous in their composition to shell. The 

 metallic lustre which the skin of the Vaagmaer displays is doubt- 

 less owing to a great number of surfaces from which the incident 

 ray is reflected, the rays transmitted through one prism being 

 reflected from the surfaces of those which lie beneath it." 



These fibres, which give the metallic lustre to the external sur- 

 face of the body and to the anterior surface of the iris *, appear 

 to me to be similar, but on a much larger scale, to the crystal- 

 looking spicula which impart the metallic lustre to the scales, to 

 the anterior surface of the iris, and to the membrane between the 

 choroid and sclerotic coats of the eyeball in some fishes. The 

 external surface of the small portion of each scale which is not 

 overlapped by its fellows is, in the haddock [Morrhua aglefinvs) 

 invested by a structu.re bearing a great affinity to the epidermic 

 layer of the Vaagmaer. This structure consists of a membrane 

 or thin layer having little spots of dark pigment cells placed at 

 short and nearly equal distances from each other, each spot pre- 

 senting in general a stellated arrangement. Imbedded and fixed 

 on the surface of this membrane are numerous small bodies, 



* In the Vaagmaer I observed no metallic-looking layer between the 

 sclerotic and choroid coat of the eyeball. 



