472 Prof. Reid on the Vogmarus Islandicus. 
several times longer than they are broad, and measuring in length 
from ;,5gth to 745th of an inch, which, when detached and 
mixed with water, give it a milky appearance. In the colouring 
layer on the anterior surface of the iris and in the metallic-looking 
layer between the choroid and sclerotic in the eyeball of the had- 
dock, the cod (Morrhua vulgaris), the flounder (Platessa flesus), 
and the common dab (Platessa limanda), these spicular-looking 
bodies are very numerous, are arranged in bundles, and are con- 
nected together by a substance having no definite structure. The 
colouring layer between the choroid and sclerotic has a fibrous 
appearance from the manner in which these bodies and their 
connecting substance are arranged. This layer in the iris is not 
so distinctly fibrous in its arrangement as that between the cho- 
roid and sclerotic. In the common dab they are, in the latter 
position, similar to those from the scale of the haddock. The 
spicular-looking bodies that give the metallic lustre to the silvery 
membrane lining the abdomen in some fishes, and also placed 
below the external integuments in others as in the haddock, 
are considerably smaller than those on the scales and in the eye- 
ball. These colour-giving fibres seem to be commonly acid 
as crystals. Ehrenberg states that the colouring matter of the 
peritoneal membrane of the fish consists of prismatic erystals ten 
times as long as they are thick, the longest. of which are about 
gth of a line in length, but this varies in different kinds of fish ; 
and similar crystals, but somewhat larger, are obtained from the 
silvery membrane of the sclerotic and of the anterior surface of 
the iris*. Henle + and Hannover}, in speaking of those in the 
metallic-looking layers of the eyeball in fishes, term them erystals. 
Mandl states that “the silvery matter disposed on the inferior 
surface of the scale upon a peculiar membrane consists of erystals ;” 
and he has given a representation of them in fig. 8. of pl. 10 of his 
memoir on the Appendices of the Skin §. | | 
* Poggendorff’s Annalen der Physik und Chemie, Band xxvii. 8. 468-9, 
1833. H. Rose analysed some of this colouring substance obtained from 
the pike furnished to him by Ehrenberg, and arrived at the conclusion that 
it was a peculiar organic substance (opus cit. pp. 470-1). 
+ Miiller’s Archiv fiir Anatomie, Physiologie, &c. Jahrgang, 1839, 
S. 387. 
t Miiller’s Archiv fiir 1840, p. 332. 
§ Mandl’s Anatomie Microscopique. Mémoire sur la Structure intime 
des Appendices tégumentaires, p. 89, 1840. Dr. Drummond (Transactions 
of the Royal Society of Edinburgh, vol. vii. p. 377, 1815), struck with the 
peculiar revolving movements which these spicula obtained from the scales 
and eyes, like so many other minute bodies when suspended in fluid, exhibit, 
was inclined to believe that they are endowed with ‘ animaleular life.” 
Reaumur (Mémoires de l’Académie Royale des Sciences, 1716, p. 229) has 
given a description of this silvery matter in the scales and the abdominal 
membrane of fishes, but he did not detect the form of these spicula, and he 
supposed that they were placed within tubes. 
