ATTEMPT TO DEDUCE VERTEBRATE EYES FROM THE SKIN. 355 
in the diagram. These are, however, now secondarily spe- 
cialised. 
It was an integral part of my theory, not only that the 
accumulation of pigment granules in the illuminated spots 
gave rise to the sensory visual areas in the epithelium by the 
irritation caused by their passage between the epithelial cells, 
but also that the excessive discharge of such granules supplied 
or helped to supply the refractive matter for a dioptric 
apparatus. This supposition entirely harmonises with this 
suggested deduction of the Vertebrate eye directly from the 
epidermis. 
When a certain area began to form a retina, i.e. in the 
earlier stages of the condition shown in Diagram II, the excess 
of pigment would pass out between the sensory cells, and 
would supply so much matter to the epidermis cells outside 
the retina; here it would be clarified, as the pigment is 
typically clarified in the epidermis, and added to the thickness 
of the refractive layers. As the sensory cells multiplied, and 
were further cuticularised as rods, and the relation. between 
them and the irritating chromatophores became more special- 
ised, the way to the exterior would be barred, and the necessary 
material would have to be brought in from the circumference 
of the retina. 
We have probably to look to the long cells depicted in the 
diagram for the bringing of the matter used in forming the 
harder refractive portions of the primitive lens. But, in 
addition, pigmented cells would almost certainly travel into 
the cavity of the eye along the connective-tissue strands 
which accompanied the nerve and blood-vessels. The rapid 
clarifying of this pigmented matter in the fluid contained in 
the space between the lens and the retina would give rise to a 
slimy mass, the rudiments of the vitreous body. The deriva- 
tives of this intrusive connective tissue would be found in the 
processus falciformis and pecten, which still convey pigment 
into those eyes that retain such structures. As the eye ad- 
vanced in specialisation, and this important channel for con- 
veying pigment into the eye to supply material for the vitreous 
