46 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
the most noticeable portion of the tectum, especially in young animals, 
The nuclei are closely crowded together, with a definite arrangement 
due to the radially directed processes of the ependymal cells, which pass 
through all the layers from the ventricle tothe pia. Only one type of 
cell body (Fig. 22, p) is evident, that being the small and rounded 
form ; in Golgi preparations, it is slightly pear-shaped, and resembles 
much the ependymal cell. But since the cells of this layer have pro- 
cesses of a number of types, they cannot all be, as Fusari (’96) main- 
tained, ependymal cells. They may fibrillate in any or all of the layers 
outside the sixth. In Golgi preparations a very few spindle cells, like 
those in layers 4 and 5, appear. Some of the peripheral cells (Fig. 22, c) 
of this layer, as well as the very deep ones, may send to the surface a 
process which ends in branching fibrillations beneath the pia.. The 
fibres from other cells were found to break up in layers 3, 4, and 5. 
These fibres are often impregnated when none of their processes take the 
silver, or vice versa. The cells next to adjacent layers, whether the 
deeper or those nearer the periphery, are more likely to become impreg- 
nated than those in the middle of the layer. 
The innermost layer (7), less dense than any of the preceding, is 
composed of the bodies of the ependymal cells and the basal portions of 
their processes. A reticulate portion of this layer (next to layer 6) is 
not apparent in young specimens, and so I have not recognized it as 
a separate layer, but have included in layer 7 all that lies between the 
gray layer (6) and the ventricle. 
In the adult brain there are scattered through this loose layer a few 
large-bodied very irregular eells (Fig. 22, 7), each having a multitude 
of long beaded processes. I was unable to discover any neurite con- 
nected with these cells. 
In order to simplify the diagram (Fig. 22), I have omitted in all cases 
the free fibrillations. In most impregnations where there are any at all, 
there are so many that only a few can be traced to any definite 
medullated layer. Layer 3, however, certainly contains, among other 
fibrillations, free branches from the optic layer (2). In layers 3 and 4 
free fibrillations of fibres from cells in layer 5 are doubtful, because 
any one of the many cells in the granular layer (6) may have its fibre 
impregnated though itself remaining clear. 
Between the fillet layer (5) and the optic layer (2) there are two 
especially dense fibrillar regions corresponding in genezal to the two 
bundles of dividing processes which arise from the cells of the nidulus 
corticalis. 
