26 SCHULTZE, ON THE RETINA. 
whose apex is coloured with a diffuse yellow pigment. Both 
these elements, however, it would seem, according to Schultze, 
should be regarded as “ cones.” According to H. Miiller, 
the retina of the chameleon contains only elements of one 
kind, which must also be regarded as cones. In the cones of 
Anguis fragilis, which have been subjected to osmic acid, 
and, apparently, according to Miller, in the chameleon, a 
peculiar differentiation of the contents of the inner segment 
of the cones is observable, in the appearance of a conical, 
strongly refractive body, the base of which is directed out- 
wards, whilst the pointed proximal extremity looks towards 
the membrana limitans externa, though it does not actually 
reach it.* These bodies were supposed by Miiller to repre- 
sent cell-nuclei, but M. Schultze suggests that they are re- 
fracting lenses. 
Throughout the amphibia a great uniformity exists in the 
retinal elements. Amongst numerous colossal “rods” are 
lodged a few very minute “ cones,” each of which contains a 
minute-coloured or colourless spherule. 
M. Schultze confirms Henle’s discovery of the presence of 
one or more ¢ransverse lines in the outer granules, or rather 
on those of the outer granules which are connected with the 
“rods,” as they are not found on those belonging to the 
*cones.”” These markings appear to be absent in all other 
vertebrates. 
A very full account of the structure and relations of the 
black pigmentary layer is given, and reasons shown for its 
being regarded as an element, not of the choroid, but of the 
retina itself. It consists essentially of a layer of cells contain- 
ing black pigment, and which send down fine filamentary 
processes, like the pile of velvet, to fill up the spaces between 
the outer segments of the “ rods” and “ cones.” 
The paper then proceeds to give an account of the arrange- 
ment, &c., of the ‘‘ cones,” which alone constitute the perci- 
plent stratum in the macula lutea. It is shown that as the 
border of this spot is approached the number of “ rods,” in 
proportion to that of the “cones,” gradually and regularly 
diminishes, until at last the former cease altogether, whilst at 
the same time the “cones ” themselves become longer and 
slenderer up to the centre of the macula; the direction, also, 
of the cone-fibres becoming more and more oblique as they 
radiate, as it were, from the centre of the macula. As is now 
well known, the layer of “ cones” is continuous over the so- 
* This is probably the “albuminous substance which, in chromic-acid 
preparations, retires as an opaque granular mass towards the outer end of the 
body of the cones,” noticed by Mr. Hulke (‘ Proc. Roy. Soc.,’ xiii, p. 109). 
