No. 1.] EYES OF ARTHROPODS. 143 
In the larvze, however, after some modes of treatment, they 
appear to be much smaller and stain more deeply. They then 
resemble the small dark cells which immediately surround the 
medulla of the brain and the ventral nerve cord. 
The optic ganglion of the late embryonic, or early larval, stages 
does not undergo any noteworthy change until toward the be- 
ginning of the pupal period. I never succeeded in finding or 
raising pupe, but feel confident that the oldest larvae obtained 
had about reached that stage. A view of the dorsal surface of 
part of the brain and optic ganglion at this period is shown 
in “Pl. LX, Fig; 40; and sections of itm shila, Pigs. 49 
and 53. 
In Fig. 40 we see beneath the crown of ganglion cells the 
faint outline of the medulla, and still further below, the con- 
tinuation of their distal ends into the optic nerves. The 
ganglion cells of the second segment, o. g.2, now form a semi- 
circular band that almost encloses the other two. They are 
recognized in sections by the clear protoplasm of their colum- 
nar cells (Figs. 49 and 50). 
The cells of the third segment are crowded toward the brain, 
where they form a narrow collar around the stalk of the optic 
ganglion. Above the middle of the stalk, the band lies at the 
bottom of a cavity, the roof of which is formed by over-arching 
ganglion cells (Fig. 50, o. g.8). Towards its anterior end it is 
wider and folded double (Fig. 49, 0. g.3). It is directly continu- 
ous on the one hand with the cells of the second segment, and 
on the other, with a broad layer of large scattering cells that 
fill up the space between it and the third segment (Figs. 40, 49 
and 50). 
Horizontal sections below the crown of nerve cells have a 
wedge-shaped outline in which the medullze have much the 
same arrangement as in Fig. 48. Fig. 51 represents such a 
section at the posterior edge of which is shown a part of the 
second ganglion segment. A section a little above this (Fig. 
52) shows part of the second and first segments, and finally a 
still more dorsal section (Fig. 53) shows the second and 
third. 
In Figs. 49 and 50 the optic ganglion is seen in two vertical 
sections, the first, near the anterior edge, the second, near the 
middle. By comparing these sections with the surface view 
