146 DK. COBBOLD ON THE EYE OE THE COD-EISH. 



the densely laminated character of its substance have proved erro- 

 neous, and that the numerous layers which his beautiful prepara- 

 tions of the vitreous body showed were only due to the coagulating 

 agency of the strong chromic-acid solutions in which the eyeballs 

 had been kept immersed before the sections were made. At a meet- 

 ing of the Physiological Society of Edinburgh in 1851, 1 took occa- 

 sion, in Dr. Hannover's presence, to point out this circumstance, 

 and also adduced other evidences to show the erroneousness of his 

 conclusions. The well-known fact, that by puncturing the vitreous 

 mass in a fresh state we can draw off, as it were, the great bulk 

 of its fluid contents, is sufficient in itself to demonstrate that the 

 vitreous body is not made up of membranous laminae ; but, at the 

 same time, there can be no doubt, as my own investigations have 

 shown, that the inner layer of the hyaloid tunic sends off a few 

 prolongations into the substance of the vitreous mass. Probably 

 these extensions form the walls of enormously enlarged cells ; but 

 this is a point which I have not been able to determine. 



The principal points, however, to which I now wish to draw 

 attention are such as have reference to the occurrence of parasitic 

 formations within the cartilaginous matrix of the sclerotic coat, 

 to the structure and functions of the so-called choroid gland, and 

 more particularly to certain artificially produced phenomena in 

 connexion with the large and remarkable twin-cones of the retina. 

 The views which I shall here subscribe in regard to the nature of 

 the choroid gland are directly at variance with the commonly 

 received opinions, and offer, I think, an intelligible explanation in 

 regard to a singularly obscure subject. 



(1.) If the external fibrous and internal separable layers be de- 

 tached from the true cartilaginous matrix of the sclerotic of the Cod, 

 it will frequently be observed, in large eyes at least, that the latter 

 contains within it certain oval, rounded, and more or less stellate- 

 looking bodies of a dense, milk-white colour. Their size varies from 

 that of a pin's head to that of a pea ; and when submitted to high 

 magnifying powers, they an; found to contain a multitude of minute 

 cellules, which have an average individual measurement of about 

 the 3 Hi of an inch. All of them arc oval in shape, and contain 

 double nuclei, placed side by side; at one end of the cell-cavity, 

 which also contains a pale-yol low-coloured fluid surrounding the 

 nuclei. So tar as I am aware, these bodies have never been de- 

 . cribed by observers in this country; but they arc manifestly the 

 o-called psoroBpermia f which have been carefully investigated on 

 the continent by Muller, Dujardin, Greplin, and others. Tho 



