THE LEEOHES OF JAPAN. _ 403 
Comparing now the eye with one of its serial homologues, 
a segmental sense-organ, we find that the axial fibres occupy 
the same position with relation to the nerve and the large 
clear cells as the sensory cells of the segmental sense-organ. 
What is more natural than to regard the axial fibres as the 
sensory cells of the eye? I have sections in which the sensory 
cells of the segmental sense-organ could scarcely be distin- 
guished if placed side by side with the axial fibres. Nuclei 
are seen along the axis of the eye, which appear to occupy the 
enlarged ends of the axial cells. This is best seen in deeper 
cells, which appear to be continuous with the fibres of the 
optic nerve. In none of my sections have I been able to trace 
the axial fibres (or cells) up to the epidermal cap, but I do not 
think it certain that they do not reach the shorter central cells 
of the cap. If they are completely separated from the epi- 
dermis, this would not of course be any obstacle in the way of 
accepting the view I have presented. 
In the epidermal cap it is necessary to distinguish a central 
or apical area of relatively short and nearly perpendicular 
cells from a border ring of longer and strongly convergent 
cells. The cells of one area pass insensibly into those of the 
other, the length and degree of convergence increasing from 
the centre outward, so that they cannot be said to be sharply 
defined. The short, refractive, rod-like terminations of the 
central cells to which attention has already been called, enable 
one, however, to distinguish quite easily the two areas. Ina 
retracted state the cells of the outer area, or border ring, are 
strongly inclined towards a horizontal position; and when 
seen from the surface they appear to radiate from the central 
area precisely as they are represented in Leydig’s figures. 
The central area then corresponds to what Leydig mistook 
for a perforation of the epidermal cap, in which the axis-fibres 
terminated. 
From this point of view the eye appeared to be a sac-like 
invagination of the skin, in which the epidermis was repre- 
sented by an inner wall of large clear cells and the corium by 
a thin limiting membrane (“ sclerotica’’) and a thicker pig- 
