Cuap. II. FORMATION OF THE ORGANS. 585 
increase in prominence, and its wall grows thick, (Pl. 12, fig. 6, /,) without any 
change in its shape, except that its base becomes narrowed, so as considerably 
to lessen the channel (Pl. 21, fig. 28, ¢) of communication with the optic lobe. 
The pedicel does not meet the hernia at its centre, but at its lower side (Pl. 21, 
28, c). At this stage the eyes may be described as_ pedicellated, asymmetrical, 
globular herniz projecting from the lower side of the optic lobes of the brain. 
The musculo-cutaneous layer (PI. 21, fig. 28, 2) follows closely the constrictions 
of the hernia, and in this manner, embracing it closely, forms a sheath about it. 
Presently the wall at the lower side of the hernia begins to be depressed, as if 
it were pushed obliquely inward by some external force, thus producing a double- 
walled cup, attached by its side to a pedicel. By degrees the depression grows 
deeper and deeper, and the outer wall (Pl. 24, fig. 8, 4%) approaches the mner one 
(i) till they meet. A thickening of the musculo-cutaneous layer constantly follows 
the sinking wall, and at the time the two walls meet it forms a spheroidal body, 
the crystalline lens, (fig. 8, %°,) moulded, as it were, in the cup of the eye. The 
depression at first extends for a short distance along the pedicel, but it is merely 
a narrow furrow, which has the appearance of being continuous with the channel 
(fig. 8, 7°) of the pedicel; however, it eventually disappears, as the inferior 
diverging borders of the cup approach each other. 
The passage way along the pedicel, the optic nerve of the eye, has by this 
time become quite small (PI. 24, fig. 7, 4°); and, in consequence of the bending 
of the pedicel in a downward direction, appears, further ward, totally below the 
eye, so as to allow a view into its cavity without looking through any portion of 
the cup. Soon the cup-shaped hernia, the retina of the eye, has approximated its 
interrupted inferior borders, till they are brought in contact, (Pl. 13, fig. 2 and 
3,) and thus the capsule of the crystalline lens is completed. The point of junc- 
tion of the borders just mentioned is not obliterated at once; but after a short 
time all trace of it seems to be gone. The borders of the sheath or orbit, 
formed by the musculo-cutaneous layer, have become contracted around the crys- 
talline lens so as to overlap it, except at the fold on the side of the eye, where 
the optic nerve joins the retina. The fold subsequently becomes very conspicu- 
ous as a white band running from the lens toward the posterior side of the eye, 
in the midst of black pigment (Pl. 24, fig. 11). Soon after this, the eyes become 
circular, and a layer of black pigment develops upon the exterior surface of 
the retina, (Pl. 24, fig. 9a,) and therefore on the inner face of the orbit, the 
future membrana choroidea. The pigment does not develop over the fold which 
runs from the crystalline lens to the optic nerve, and consequently a white, broad 
streak is left on the lower side of the eye (Pl. 14, fig. 5). In a little older 
phase, what we have hitherto called the crystalline lens turns out to be not only 
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