ATTEMPT TO DEDUCE VERTEBRATE EYES FROM THE SKIN. 369 
been greatly strengthened if it had been possible to incorpo- 
rate some of the more direct evidence in favour of the theory 
from which they start. This evidence is, however, cumulative ; 
and in endeavouring, first, to show that the chief types of eye 
are both morphologically and physiologically explicable by this 
theory, I merely begin with that portion of the evidence 
which came readiest to hand. 
In selecting eyes for analysis in subsequent contributions to 
this subject I shall not follow any systematic order; my 
primary object not being any comparative study of eyes, but 
merely the detailed working out of the observations which I 
have made, which seem to me to afford evidence of the truth 
of my theory of the origin of light sensations. 
EXPLANATION OF PLATE 22, 
Illustrating Mr. H. M. Bernard’s paper, “ An Attempt to 
deduce the Vertebrate Eyes from the Skin.” 
Fic. 1.—Diagrammatic representation of a pineal eye regarded as an 
invagination of a simple palisade epithelium. The pigmented contents of the 
chromatophores of the cutis find their way in the skin to the surface, where 
they form a layer of slime (yellow), and in the eye into the cavity of the 
invagination, where they form a slimy vitreous humour. 
Fic. 2.—Hypothetical early stage in the evolution of the Vertebrate eye 
proper. Externally the palisade layer of the skin has budded off layers of 
cells, which as “ prickle-cells”” absorb the pigment and other matter passing 
through the palisade cells, and, dying, become horny scales. The nerves of 
the skin (.) no longer end in the palisade layer, but among the prickle-cells. 
Hence, when the palisade cells become retinal cells stimulated by the passage 
of the pigmented granules, the nerves have to bend back. The retinal pali- 
sade cells early become cuticularised, apparently in order to oppose more 
effectively the outward streaming of the pigmented granules. The nerves 
are already grouped into a solid strand, and form a kind of handle to the 
spoon-shaped retina which is being bulged in by the accumulation of slimy 
maiter in the epidermal cleft which has arisen above the retina. Into the 
