Cuap. II. FORMATION OF THE ORGANS. 589 
variable degrees of intensity. This color is situated totally within the large meso- 
blasts of the columnar cells which compose the stratum (see Pl. 21, fig. 33, A, 7, 
fic. 33a, a, 6, c). The combined strata of the retina (PI. 22, fig. 8, 4) with the mem- 
brana Jacobi (vy) have a uniform thickness throughout, except at the anterior bor- 
der, where they suddenly thin out and come to a sharp terminating edge, (7',) at a 
short distance behind the base of the iris. Opposite the entrance of the optic 
nerve, (/’,) the retina preserves the same uniformity as elsewhere, nor do there 
appear to be any nervous fibres prolonged through it from the optic nerve; but 
this point wants further special investigation. The optic nerve, (/',) as well as 
the whole retina, is hardly consistent enough to hold together, when separated 
from the surrounding envelopes. Just within the retina, there is a very thin, stri- 
ated layer, (7,) composed of wavy fibres, which apparently radiate from the optic 
nerve (/') in every direction, and extend to the anterior edge (?') of the- retina. 
In another place it will be shown in detail, that these fibres are not prolon- 
gations from the optic nerve, but belong to the inner layer of nervous cells, of 
which they are tail-like prolongations (see Pl. 21, fig. 33, 4). Next within the layer 
of wavy fibres (Pl. 22, fig. 8, 7) is the membrana hyaloidea, (/, /',) forming a closed 
sac, and linmg the whole internal surface of the retina and the back of the crys- 
talline lens (/). This membrane lies close against the retina over its whole extent, 
even to within a very short distance of the anterior edge of the membrana Jac- 
obi, (g',) where it folds backward and passes (/") close behind the crystalline 
lens, (4) where it may be traced as readily as at any other part. The soft, 
thick, and tender nature of this membrane readily distinguishes it from the exces- 
sively thin, tough, glassy, glittering, and elastic triple membrane which forms the 
capsule (m) of the crystalline lens. The three membranes composing the capsule 
(m) of the crystalline lens adhere very closely to each other, so that it is very 
difficult to separate them. At the spot where the membrana hyaloidea comes in 
contact with the crystalline lens, the membrane of the capsule sends off a layer 
forward and centrifugally, which joins the hyaloidea as far as its first bend, (/*,) 
and thence, turning suddenly upon itself, passes forward and centripetally before the 
edge (n') of the membrana pupillaris, (7,) by which it is closely overlapped, and 
to which it adheres very tenaciously, and terminates a little behind the free edge 
of the iris. This portion of the membrane of the capsule clings so closely to 
the hyaloidea, especially at the angle (/*) where it reverts to pass before the 
membrana pupillaris, that, were it not for the great difference in structure between 
the two, as we have pointed out above, it might easily be mistaken for a con- 
tinuation of the membrana hyaloidea, as it has been asserted to be, in the eye 
of Mammalia. 
The crystallme lens, (/,) when seen in profile through a line perpendicular to 
