THE EYE OF PERIPATUS 165 
surface forms a dome-shaped protuberance on the skin. The 
whole of this bulge appears to be occupied by the lens. In 
sections which have not been depigmented (see left side of 
fig. 1) the eye appears to be made up of three regions—the 
lens, the region previously known as the retina (or rod region), 
and the so-called optic ganglion. Now it will clear matters 
up at once if we state that the rod layer does not consist 
of cells but only of parts of cells—i.e. the distal halves 
of cells whose nuclei le internally to the pigment. In 
other words, the so-called optic ganglion plus the 
rod layer together make up the retina. The units 
of these layers are not separated by a layer of pigment ; the 
pigment is actually enclosed within the cells (see fig. 2). 
The Cuticle overlying the eye (fig. 1, Cut.) differs 
from that of the ‘surrounding regions in being free from the 
small projections so characteristic elsewhere. Not only are 
the minute spines absent, but the dermal papillae which are 
present over the entire body wall are missing here. 
The Epidermis is continued over the eye to from the 
Cornea (fig. 1, Cor.). Most of the cells of the general 
epidermis are somewhat cubical or pyramidal in form, with 
large nuclei. The corneal cells are very different, beg quite 
flat. The nuclei are decidedly compressed and the protoplasm 
is reduced in amount. 
The Subcorneal layer of cells may be said to form 
a capsule which encloses the lens. It is seen as a well-marked 
layer where it covers the lens and extends down over the rod 
layer (fig. 1, Sub. Cor.). There is nothing of importance to 
add further regarding it except that in the development of the 
eye it formed the outer portion of a complete vesicle, the 
proximal cells of which have given rise to the retina (see 
fig. 5). 
The Lens is non-cellular and forms a homogeneous mass 
which stains readily with eosin. The face towards the retina 
appears almost flat in well-preserved sections, whilst the distal 
surface is highly convex, so that the entire structure is practi- 
cally a dome. In all the well-preserved sections the proximal 
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