No. 383.] BASIS FOR A THEORY OF COLOR VISION. 841 
way similar to each other except as to size. A single retinal 
cell is shown in side view in Fig. 1— and a section of the retina 
in Fig. 6 ; this section is cut through ocellus II (Fig. 5) verti- 
cal to the plane of the paper and at right angles to the zigzag 
lines of pigment. On the right side of Fig. 5 these cells are 
shown, on a somewhat larger scale, in the three positions they 
occupy in the corresponding ocelli. An enlarged section nearly 
parallel with the surface of ocellus II (Fig. 5) is shown in Fig. 7. 
On the right of this figure the section plane is deeper, show- 
Fic. 4.— Diagram to show th g t of the rods in th lli of Acilius, and the way in which 
the aiats Esh a gelia resemble in h in th P di 5 ti 
ing the argentea and the ends of the rod cells. A compar- 
ison of these figures shows that the rods are arranged in zigzag 
rows, fenced off on either side by a band of pigment, and 
with a concave reflecting membrane beneath each row. The 
rods contain parallel fibrils (Fig. 7), and they are conical both 
in cross and in longitudinal section (Fig. 5,-I* and II*). The 
rods in the centre of the retina are very small, gradually in- 
creasing in size towards the periphery. We have here, there- 
fore, a most beautiful arrangement, one obviously adapted to 
bring the rods, and the rods only, into definite relations to the 
rays of light. 
