i12 PATTEN. [VoL. II. 
of the cells. At the outer ends of the cells, the fibres are 
straighter and slightly enlarged. The pigment stops at this 
place, but the fibres are continued onward, nearly parallel with 
one another, over the outer surface of the rods (Figs. 54 and 57). 
The inner ends of the retinophorz are continuous with coarse 
fibres composed of the inward prolongations cf the external 
and axial nerves. There are in rare cases smaller bundles 
which, on their way to the more peripheral portion of the ret- 
ina, pass over the inner third of some of the retinal cells at a 
sharp angle. Some of these fibres impinge upon a retinal cell 
near the primary nucleus and join the other external nerve 
fibres belonging to that cell. Such nerve fibres occasionally 
cling to isolated cells, and one might erroneously infer that 
they entered the cell opposite the nucleus. 
About the time the clear area begins to be invaginated a 
number of deeply stained granules appear on the periphery of 
each ocellar thickening. They increase in size from the surface 
of the ectoderm inwards, and each one is surrounded by a clear 
area (Pl. XI., Figs. 63-66, and Pl. XIII., Figs. 32, 33, ad. 2). 
I have found similar products in the optic ganglia and in the 
ventral nerve chord. The manner in which they absorb color- 
ing matter and their general appearance, together with the fact 
that they seem to be most abundant in tissues undergoing ret- 
rogressive changes, suggest that they may be degenerating 
nuclei. 
Eye VI. 
Eye VI. first appears in the posterior part of the third segment 
of the optic plate as a triangular depression, or clear area, the 
apex of which is directed dorsally and slightly forwards. On its 
ventral and posterior side, is a round dark area with a small clear 
spot in the centre. The depression soon becomes sickle-shaped, 
and finally circular, completely surrounding the dark area (Fig. 
5a). Ina little later stage (Fig. 6a) the furrows separating 
the eyes from each other have disappeared. The clear space is 
divided into two parts by a dark ridge, on the dorsal side of 
which is that part of the clear area that appeared first; it is 
now somewhat rhomboidal, contains a dark ridge composed of 
a double row of nuclei, and is divided into four pits, 1, 2, 3, 4. 
The ventral part of the eye is composed of an irregular clear 
