320 
FREDA BAGE. 
(figs. 4, 6, 7, ell}). It is less definite in shape than the 
paraboloid, and in some preparations both the oil globule and 
paraboloid press in on each side causing the ellipsoid to 
become biconcave (fig. 5, ell}). 
In transverse section the ellipsoids are somewhat penta- 
gonal in shape, owing to the pressure of the cones agaiust 
one another. In one preparation (fig. 9, ell}), fixed with 
acetic bichromate and stained rather deeply with picro- 
indigo-carmine, the ellipsoids of the ordinary single cones 
are stained dark green in colour and show no vacuolation. 
The paraboloid (figs. 4, 5. 6, par. 1 ) is very definitely oval 
in shape and is bounded by a thick wall (figs. 5 and 6, w.p.), 
which stains distinctly. In the picro-nigrosine preparations 
(fig. 5) it is purple in colour. The contents of the paraboloid 
stain much less readily, though in all cases there appears to 
be a slight coagulation which can sometimes be resolved into a 
network of fibrils (figs. 5, 6 and 7 ,f.n.). A definite basal 
part of the cone (figs. 5 and 6, b.c.) is seen between the 
paraboloid and the external limiting membrane. It is some- 
what granular in appearance in the picro-nigrosine sections 
and simply forms the ground-work or supporting structure 
in which the paraboloid is embedded, this basal cytoplasm 
being continuous with that passing over the nucleus 
(fig. 7, c.n.) into the cone-cell fibril. When the cone is cut 
through its long axis it is seen that the paraboloid almost, or 
quite, touches the nucleus (fig. 7). 
The size of the ordinary single cones varies somewhat in 
different situations. Over the greater part of the retina they 
measure about 40 p in length. In the fovea centralis, where 
only cones of this type are present, they are, as already 
mentioned, very densely packed and somewhat longer and 
more slender, those of the macula lutea outside the central 
fovea being intermediate in size and form. 
(2) The Small Single Cones (fig. 8). 
Quite small cones (fig. 8, S.S.G.) are to be seen here and 
there among the ordinary single ones. These, in spite of 
