WILLIAMS : MIGRATION OF EYE IN PSEUDOPLEUEONEGTES. 43 



beiu» directed outward. From this smaller end processes ran both au- 

 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, 8) with one process directed outward and fibrillat- 

 iug in layer 1, and one or more processes directed inward. Cells lilie 

 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. (b) Pyri- 

 form cells (Fig. 22, e) with all the processes directed inward and the 

 ends of the fibrillations reaching into layer 4. (f) Eouuded 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, t]) the reverse of those denominated e 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, 0) 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 oft" 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 nidulua corticalis (nid. ctx.) 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. 



