PROCEEDINGS OF SOCIETIES. 287 
the choroid, and their sides are separated by pigmented processes, 
prolonged from the inner surface of the choroid between them to 
the line that marks the union of the shaft with the inner segment. 
The effect of this is that the shafts are completely insulated, and 
rays entering one shaft are prevented passing out of it into neigh- 
bouring shafts. 
5. The inner segment of the rods and cones, or body (the ap- 
pendage of some microscopists), has a generally flask-shaped form, 
longer and more tapering in the rods, shorter and stouter in the 
cones. It is much paler and less conspicuous than the shaft. It 
fits in an aperture in the membrana limitans externa. 
Its inner end always encloses, or is connected by an inter- 
mediate band with an outer granule which lies in or below the 
level of the membrana limitans externa. Its outer end, in cones 
only, contains a spherical bead nearly colourless in the frog and 
blindworm, brilliantly coloured in the turtle and water- and land- 
tortoises, and absent from the common snake and Spanish Gecko. 
In addition to this bead, where present, and the outer granule, 
the body contains an albuminous substance which in chromic acid 
preparations retires as an opaque granular mass towards the outer 
end of the body. The inner end of the body is prolonged inwards, 
in the form of a pale, delicate fibre, which was sometimes followed 
through the layer of inner granules into the granular layer. It 
does not appear to be structurally connected with the inner gra- 
nules. It is essentially distinct from Miiller’s radial fibres, and 
bears a considerable resemblance to the axis-cylinder of nerve. 
That it ever proceeds from the outer granule associated with the 
rod- or cone-body is doubtful, from the consideration («) that 
where the body is large, and the granule lies within at some 
distance from its contour, the fibre is seen to leave the inner end 
of the body distinct from the granule, and (/) that the fibre 
appears to proceed from the outer granule only where the body is 
small, as in the frog, and where the granule does not lie within 
the body, but is joined to this by a band. Ritter’s axial fibres are 
artificial products. 
6. The “outer granules” are large, circular, nucleated cells. 
Each cell is so intimately associated with a rod- or cone-body that 
it forms an integral part of it. 
7. The intergranular layer is a web of connective fibre. It 
contains nuclei. 
8. The inner granules are roundish, in chromic acid prepara- 
tions polygonal cells. They differ from the outer granules by 
their higher refraction, by the absence of a nucleus, and by 
receiving a deeper stain from carmine. They lie in areole of 
connective tissue derived from Miiller’s radial fibres, and from 
the intergranular and granular layer. They are more numerous 
than the outer granules, and consequently than the rods and 
cones. 
9. The granular layer is a very close fibrous web derived in part 
from Miiller’s radial fibres, and from other fibres proceeding from 
