78 THE ORIGIN OF VERTEBRATES 
is much larger than the left. This difference between right and left 
indicates a greater degeneration on the left side, and points distinctly 
to a close relationship between the nerve-masses known as ganglia 
habenule and the median eyes. In my opinion this ganglion is, in 
part, at all events, the optic ganglion of the median eye on each side. 
It is built up on the same type as the optic ganglia of invertebrate 
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Fic, 32.—Eym or Acinivus Larva, WITH Fic, 33.—PinEau Eyz or AMMOCG@TES, 
irs Opric GANGLION. WITH 1Ts Ganglion Habenule. 
On the right side the nerve end-cells On the left side the eye is drawn as it 
have been drawn free from pigment. appeared in the section. On the right 
side I have removed the pigment from 
the nerve end-cells, and drawn the eye 
as, in my opinion, it would appear if 
it were functional. 
simple eyes, with a cortex of small round cells and a medulla of fine 
nerve-fibres. Into this ganglion, on the right side, there passes a very 
well-defined nerve—the nerve of the dorsal eye. The eye itself with 
its nerve, pn., and its optic ganglion, g.h.r., is beautifully shown by 
means of a horizontal section through the head of Ammoccetes 
(Fig. 31). Originally, as described by Scott, the eye stood vertically 
