WILLIAMS: MIGRATION OF EYE IN PSEUDOPLEURONECTES, 37 
brain and eyes farther advanced, and Figure 11 (from an adult) shows 
it completed. 
In the essentially adult condition of Stage IV., as shown in a front view 
of the modelled brain and optic nerves (Figure /’), the left eye has passed 
so far to the right side that, taking into consideration the high degree of 
mobility of the eye its field of vision almost coincides with that of 
the right eye. The optic nerves curve still more in their passage 
from chiasma to eye, and the distance is proportionately greater. 
The right cerebral lobe (cb. dx.) is seen in the figure between the eyes, 
and the left cerebral lobe (cb. s.) is seen on the right, behind the left 
eye, and below the tectum. The left olfactory lobe is covered by the 
left“eye, but the right olfactory lobe — modelled as a continuation for- 
ward of the right cerebral lobe — is seen between the two eyes. The left 
optic lobe (tet. opt. s.) in both these instances (Figures / and /’) extends 
farther anteriorly than the right. This is seen in the dorsal view of - 
the brain (Fig. 8). This figure also shows why in making cross-sec- 
tions the left lobe of the cerebrum is cut before its olfactory lobe in 
ease one begins at the anterior end. 
The optic nerve —round in cross-section in the larvae — becomes 
thrown into folds in the adult (Plate 5, Fig. 24). This condition is also 
figured by Studnicka (’97) for one of the Pleuronectidz. The cross-sec- 
tion may show as many as six or seven folds closely pressed together, 
Small neuroglia nuclei are scattered throughout the length of the nerve. 
3. Tue CHIASMA AND TRACTS WITH RELATED GANGLIA. 
The optic crossing is complete as in all teleosts. There is no inter- 
lacing of fibres, as can be seen in Figure 19 (Plate 4), which is from a 
fish in Stage IV. This is an approximately transverse section, which, 
however, cut the left side of the fish somewhat farther caudad than it 
did the right side. The plane of the section also inclines a little back- 
ward and upward, so that it coincides with the plane of the anterior part 
of the left optic tract, which slants in Figure 19 backward and upward 
on its way to the tectum. The right tract is cut crosswise, nearly at 
right angles to its course. (This is by mistake lettered n. opt. s. in 
Figure 19. Of course, as it is posterior to the chiasma, it should have 
been labeled ¢trt. opt. dx. For the second section anterior to this the 
label x. opt. s. would be correct.) The median, dorsal portion of the 
tract (trt. opt. d.) passes upward through the nidulus corticalis (to be, 
described later) on its way to the median portion of the tectum. The 
