06 W. J. DAKIX, 



referred to ; it is continued around tlie optic vesicle (PI. 6, 

 fig. 1, Con.) forming the inner wall of this (the outer being 

 formed by the epithelium), and finally persists much diminished 

 in thickness as a thin, transparent, and practically structureless 

 layer undeilying the cornea and separating this from the lens 

 (PI. 6, fig. 1, (Jo. S.). This is the "pseudo-cornea " of Patten, 

 and the " iunere Pellucidaschicht" of liawitx. Nuclei are on 

 rare occasions to be seen in it, but generally it is free from 

 the connective-tissue fibi-ils and muscle-ribrilla3, which appear 

 in that part just outside the corneal area, under the pigment- 

 mantle (PI. 0, fig. 1, M.f.). This more hyaline character is 

 in all probability due to the fact that light rays have to pa^s 

 through this layer before entering the optic vesicle. 

 . The Lens. — The lens (PI. 0, fig. 1, L.) is one of the 

 structures that gave much trouble to the early investigators, 

 but has lately been considered, entirely understood, and 

 passed over somewhat lightly. Hesse made out some new 

 and highly interesting sti-uctures, which I have been able to 

 confirm. I find, however, that the shape of the lens-cells 

 has been quite misunderstood, and the cells are certainly of 

 a very peculiar nature. 



The early authors could not determine the correct shape 

 of the lens itself. Keferstein believed it to be spherical ; 

 Hensen was uncertain, but believed it to be bi-convex ([13], 

 p. 222); Hickson considered it, however, as elliptical ([18], 

 p. 447). 



The confusion was again due to artefacts. It may be taken 

 as definitely proved that the lens is bi-convex. 'i'he distal 

 surface is, however, almost flat, whilst the proximal is very 

 convex, and may appear dome-shaped. The actual degree 

 of convexity depends largely on the contraction which has 

 taken place in the eye during fixation, and the lens, dissected 

 free from its limiting elements in a living specimen, probably 

 alters in shape considerably, since it is not of very firm con- 

 sistency. The lens is suspended from the subcorneal connective 

 tissue (PI. 6, fig. 1, Co. 8.), against which its lesser convex 

 surface is fastened. In surface view this face is circular and 



