WILLIAMS: MIGRATION OF EYE IN PSEUDOPLEURONECTES. 43 
being directed outward. From this smaller end processes ran both an- 
teriad and posteriad, the most of them parallel to the surface; one, 
however, took an oblique direction, running forward and inward, and 
reached layer 3. Neumayer represents in this optic layer spindle- 
shaped cells, the upper ends of which fibrillate in layer 1, and the 
lower in layer 3. 
The third layer contains cells of many shapes. (a) Short spindle- 
shaped cells (Fig. 22,6) with one process directed outward and fibrillat- 
ing in layer 1, and one or more processes directed inward. Cells like 
these are described by Fusari, Neumayer, and Mirto, and the last two 
authors say that the neurites are directed inward and reach the fillet 
layer. Fusari also describes a type of cell which is spindle-shaped with 
processes extending downwards and fibrillating just above the fillet 
layer. A neurite of one of these cells is figured running through the 
corona radiata of Gottsche* into the torus semi-circularis. (6) Pyri- 
form cells (Fig. 22,¢) with all the processes directed inward and the 
ends of the fibrillations reaching into layer 4. (c) Rounded cells 
(Fig. 22, €) with rather long sparsely branched processes, the outward 
process having been followed in one case into the optic-fibre layer. 
(d) Cells (Fig. 22, 7) the reverse of those denominated € in this layer, 
with fibrillations having the opposite direction and reaching to, or even 
through, the optic layer into layer 1. (e) Lying near the boundary 
between this (3) and the next deeper (4) layer were found a few cells 
(Fig. 22, @) flattened in a direction perpendicular to the surface of the 
optic lobes. Each of these possessed a process running from either end 
parallel to the surface of the tectum and sometimes a third one passing 
out towards the surface. At or near this transitional region between 
layers 3 and 4 the fibres from most cells send off short branches parallel 
to the surface. 
I have separated layers 2 and 3 because in the anterior portion of the 
tectum some fibres from the optic tract take a direct course into layer 
3 without first bending outward into layer 2. In the posterior portion 
of the tectum, however, it is not possible to distinguish these two layers. 
Bundles of large processes from the nidulus corticalis (n7d. etx.) enter 
the anterior portions of these two layers and form a prominent fibrilla- 
tion, traceable for some distance backward. These coarse, wavy processes 
are much larger than the fine fibres, which I have shown (p. 40) to be 
the neurites which make up the horizontal commissure, and there may 
be two or three of them from one cell. These coarse processes can be 
1 This is the “Stabkranz,” the descending fillet fibres. 
