The Eye of the God-fish. 203 



designated them eye- stones, and I have represented a few 

 in the upper part of Fig. 3. When I added acetic acid there 

 was neither effervescence nor disintegration, although, on the 

 other hand, the application of strong caustic potass gradually 

 caused their dissolution. Between the marsupium and the 

 vascular layers of the choroid there exists a fibrous membrane 

 coated with yellow-brown pigment cells, the latter being 

 characteristic of the lamina fusca of authors. These coloured 

 cells, shown in Fig. 4, are somewhat irregular both in form and 

 size, and contrast strongly with the true black pigment cells, 

 which are much larger and particularly abundant at the ciliary 

 margin of the choroid. One of the latter and two sarcode 

 globules are represented in the lower part of Fig. 3, magnified 

 about two hundred diameters linear. 



The vascular choroid itself consists of two distinct layers, 

 the outer one constituting the true choroid, and the inner being 

 the so-called tunica, or membrana Ruyschiana, which is partly 

 separated from the former by the intervention of a non-vascular 

 fibrous membrane, containing neither nuclei nor granules. The 

 choroid proper consists of vessels united by connective tissue, the 

 latter element being particularly abundant in the neighbourhood 

 of the vascular trunks before they suddenly divide to form the 

 so-called choroid gland ; the inner layer, or membrana Ruys- 

 chiana, is comparatively thin, becoming intimately blended 

 with the former as it approaches the ciliary circle. To the 

 naked eye the choroid gland of the cod invariably displays the 

 figure of an irregularly horseshoe-shaped band, the incomplete 

 portion of the band occupying the anterior aspect of the eye- 

 ball in relation to the longitudinal axis of the fish. In some 

 instances the continuity of the band is interrupted at two or 

 more distinct places, but in this case the lineal arrangement of 

 the independent segments combines to produce the charac- 

 teristic form above described. 



If in another fresh eye of the cod fine injections of ver- 

 milion and artificially prepared ultramarine be severally thrown 

 into the vein emerging from the optic sheath and the artery 

 entering the sclerotic immediately behind the latter, both in- 

 jections, if not too violently forced from the syringe, will be 

 found to have filled the trunks of the choroidal arteries and 

 veins as far as the inner margin of the band ; and if, there- 

 after, the eyeball is laid open by a clean tranverse cut from 

 before backwards, the true choroid being also carefully isolated 

 from all the other membranes, the operator will probably be 

 rewarded for his trouble by the production of a preparation of 

 the posterior half of the choroid very similar to the one depicted 

 in the accompanying plate (Fig. 5). The illustration, however, 

 represents the parts enlarged to twice their natural diameter, 



