122 PATTEN. [Vom iat 
plane. Hence it happens that in vertical cross-sections of the 
eye, four or five rows of large nuclei are seen near the middle of 
the retina, although the outer ends of the cells to which these 
nuclei belong are arranged with the utmost precision in two 
rows. 
The giant cells have, in the early stages (Fig. 76), short rods 
extending the whole length of their distal ends. In the full- 
grown larva these rods are longer but narrower, the proto- 
plasm of the cells having pushed its way under the inner edge of 
the rod to form a deeply pigmented heel that excludes the rays 
of light from the underlying nerve fibres (PI. X., Fig. 56). 
The large nucleus, nc, conspicuous in surface views, remains 
throughout life unaltered, except that it is perhaps a little larger 
and flatter in the older stages. It lies a little inside the middle 
of the horizontal retina, between the deep edges of the two rows 
of large cells (Figs. 81 and 86). 
The vertical retina differs principally in size from the horizon- 
tal one. It is deeply buried in the pigment at the periphery of 
the corneagen, and might be easily overlooked. It arises, as 
already pointed out, from the short bent portion of the dark 
area (Figs. 14, 15, 16). There is a second: larce ‘nuclens 
that marks, in surface views, about the point where the hori- 
zontal and vertical retinas are continuous ; but when the eye is 
well invaginated, this nucleus has changed its position to 
about the middle of the vertical retina. In the next stage (Fig. 
80), the vertical retina is reduced in size at the angle of the 
bend, so that it has apparently lost its connection with the hori- 
zontal one. At its outer end the retinal cells are well developed, 
and form a projecting mass that shelves off abruptly toward the 
dorsal appendage (PI. XIII., Fig. 80). 
In the still later stages the furrow is relatively smaller and 
more uniform in size. At the bottom of the furrow is a double 
row of large, flat cells, bearing short, broad rods placed end to end 
against those on the opposite side (Fig. 84). Outside-of them 
is a single row of smaller, cylindrical ones, bent in the form of 
a semi-circle and bearing short terminal rods. These retinal 
cells are filled with coarse, black pigment granules, so that only 
a narrow slit is left through which the light can pass to the cir- 
cular space containing the large rods (Fig. 84). 
Longitudinal vertical sections of the eye expose the arrange 
