MLEDONE. 551 
and possibly is the seat of formation of the blooa 
corpuscles. This, however, is doubtful, as its blood 
supply, from the arteries of the eye, is very limited. 
The skin which covers the eyelid, after being reflected 
over the pseudo-corneal membranes, is continued down 
the inner surface of the external muscular coat of the eye 
(fig. 78, Conjunct.). Just antericr to the cartilaginous 
capsule it is reflected on to the globe of the eye, and 
running up clothes the iris as far as the pupil. Here it 
is again reflected internally and runs down on the internal 
surface of the iris, and then over the ciliary body, and 
then is continued as the external layer of the true cornea. 
This outer layer of the two-layered cornea thus arises 
Fie. VI. Diagram showing relation 
of white body to eye and optic 
ganglion. x 1. 
from the infolded external skin of the head, while the 
internal layer is the external part of the wall of the optic 
vesicle, of which the internal part forms the retina. 
Hence the internal layer of the cornea and the retina are 
continuous. The two corneal membranes secrete the lens 
which thus is in two segments, an external smaller one 
and a larger internal. The external division is a 
seoment of a much larger sphere than is the internal, but 
the two themselves are of equal area where they adjoin 
the cornea. ‘They readily separate. The internal 
segment alone corresponds morphologically with the 
Gastropod lens. The rest of the ocular cavity is occupied 
by the vitreous body—a thick, perfectly clear and 
transparent fluid, contained in a thin membranous sac 
