370 H. M. BERNARD. 
cavity thus formed, blood-vessels and connective tissue conveying chromato- 
phores intrude, and help to supply the matter for the vitreous humour. The 
horny covering of the retina is supplied by specially long “ prickle-cells,” 
which form a kind of surface lens. 
Fic. 3.—Hypothetical stage following that shown in Fig. 2, the retina 
having bulged still further into the body, and the optic nerve (0. 2.) having 
sunk more towards the base of the invagination, the whole eye, including the 
surface lens, has been invaginated below the skin. In the stalk of the invagi- 
nation, composed of cutis, lymph-spaces commence to appear in the optic axis 
of the eye. ‘The intruding blood-vessels and connective tissue are shown 
entering the cavity of the eye with the optic nerve, and radiating strands 
towards the lens for the movements of the same are diagrammatically 
indicated. 
Fic. 4.—Shows the changes which would be required to complete the 
sensory and dioptric apparatus of the Vertebrate eye. The lymph-spaces are 
specialised into the aqueous chamber; the stalk of invagination persists as the 
ligamentum annulare (or pectinatum). The radial contraction of the tissue 
to form the iris gave rise to a fold—the rudiment of the ciliary processes. 
The lens has become isolated by the rolling round (as indicated by arrows) of 
the palisade layer of the distal portion of the eye. The portion of the 
palisade epithelium thus given up to the lens is represented as having been 
regenerated (dotted lines). 
