472 Prof. Reid on the Vogmarus Islandicus. 



several times longer than they are broad, and measuring in length 

 from xoVo*^^ *^ 7^0^^ ^^ ^^ ^^^^^ 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 metalHc-looking 

 layer between the choroid and sclerotic in the eyeball of the had- 

 dock, the cod [Morrhua vulgaris), the flounder (Platessaflesus), 

 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 regarded 

 as crystals. Ehrenberg states that the colouring matter of the 

 peritoneal membrane of the fish consists of prismatic crystals ten 

 times as long as they are thick, the longest of which are about 

 ^^g th of a line in length, but this varies in difierent 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 t and Hannover J, in speaking of those in the 

 metallic-looking layers of the eyeball in fishes, term them crystals. 

 Mandl states that " the silvery matter disposed on the inferior 

 surface of the scale upon a peculiar membrane consists of crystals/^ 

 and he has given a representation of them in fig. 8. of pi. 10 of his 

 memoir on the Appendices of the Skin§. 



* Poggendorff's Annalen der Physik und Chemie, Band xxvii. S. 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). 



t Mailer's Archiv fiir Anatomic, Physiologic, &c. Jahrgang, 1839, 

 S, 387. 



: Miiller's Archiv fur 1840, p. 332. 



§ MandFs Anatomic Microscopique. M^moire sur la Structure intime 

 des Appendices tegumentaires, 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 " animalcular life." 

 Reaumur (Memoires de 1' Academic 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 tube^. 



