Prof. Reid on the Vogmarus Islandicus. 471 
tinated together as those on the skin. I did not succeed in 
making any accurate measurements of these, but some of them 
were about s,/,5th of an inch in breadth, the greater number 
however, were narrower than this, and the longest about ;3,th of 
an inch in length. They dissolve in aqua potasse, and when sub- 
jected to the action of diluted muriatic acid under the microscope 
no bulle 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 report 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 phenomena 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 phenomena 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- 
Jess 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 eglefinus) 
invested by a structure 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 J observed no metallic-looking layer between the 
sclerotic and choroid coat of the eyeball. 
