130 PATTEN. [Vor. IL. 
retina and corneagen. They were like the similarly placed 
cells described in eyes I. and III. (Pl. XIII, Fig. 85, 0, w), and 
I do not doubt they are of the same nature, z.e. cells that have 
been pushed between the retina, and the corneagen, forming the 
rudiments of a middle layer. They never form groups of in- 
verted sensory cells, as in eyes V. and VI., or a continuous layer 
of non-sensory ones, as in a part of eye VI. 
The retinas ot both eyes are asymmetrical, as in eyes I. and 
III., in that there are more upright rods on the dorsal side of 
the retina than on the ventral (Figs. 77, 78). 
Eye II. contains a greater number of horizontal rods than eye 
IV., and the median space in which they lie is considerably 
deeper. 
The outer retinophore are long and semi-circular, and nearly 
uniform in size throughout. The innermost ones are broad, scim- 
etar-shaped cells, arranged with great regularity in two rows that 
extend the whole length of the longitudinal axis of the retina. 
Their free ends, which are bent at right angles, are almost as 
broad as the remainder of the overlying retina. In the younger 
stages, the terminal edges of the large rods are concave, and a 
considerable space is left between the two rows (Fig. 76). In 
the later stages they are rigidly straight, and the space is 
filled with a layer of densely pigmented, vertical nerve fibres, 
like those in eyes I. and III. (Fig. 78). 
In all essential particulars, the finer structure and arrange- 
ment of the retinophore and their rods, and the distribution of 
nerve fibres, is the same as in eyes I. and III. 
After the corneagen has formed a continuous layer over 
the retina, the Jarge nucleus lies just below and between the 
inner edges of the two rows of giant retinophorae. It stains 
deeply on the periphery, and contains a few coarse, deeply 
stained granules. It is always oval, with its long axis parallel 
with the long axis of the retina, and is somewhat compressed, 
‘as though forceably flattened between the two rows of cells. 
It remains in this position, unaltered, through larval life. 
Eyes II. and IV. are somewhat canoe-shaped, the retinal 
furrow being at first nearly parallel with that of eyes I. and III, 
below which they lie in the earlier stages; but they finally 
change their position for one behind the deep end of eye I. 
During this change, they rotate on their optical axis through an 
