44 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
followed backward for some little distance along distinct paths in layers 
3 and 4, and the general appearance of the fibrillations farther back 
indicates that these processes, branching continually, pass backward 
through the tectum much farther than continuity can be directly traced. 
A dendrite may branch and follow the fibrillar paths in each of the two 
layers. 
A large system of fibres also enters the same general region of the 
tectum from the axial part of the mid-brain; some of these cross from 
the opposite side of the brain in the lower part of the posterior commis- 
sure. These fibres may constitute the most anterior portion of the com- 
missura mesencephali (Herrick’s sylvian commissure) or, as I think 
more likely, they may come from the motor regions, possibly Haller’s 
anterior connective. I have not succeeded in tracing these fibres to 
any cells. 7 
In layer 4 appear the cells which are most characteristic of the tectum 
(Fig. 22,.). They were impregnated in most of the Golgi preparations. 
They are spindle-shaped, being much elongated in a radial direction, 
and have fibrillations which extend outward as far as layer 2. Some- 
times there is an impregnated process which goes from the deeper end 
of the cell into layer 5, and sometimes there is not. Neumayer and 
Mirto each state that the neurites of these spindle cells are traceable to 
the fillet layer and the fibrillations to the optic layer. Mirto describes 
cells with the same processes but with much more slender bodies. The 
spindle-shaped bodies are shown by my hematoxylin preparations to 
be very abundant indeed in this layer, only a few taking the Golgi 
impregnation in a single specimen. In this layer (4) there were also 
found sparingly cells (Fig. 22, x) with rounded bodies and processes 
which fibrillate inwards and extend into the fillet layer (5). A very few 
pyriform cells lie near the deep surface of this layer (4) and send their 
processes outward (Fig. 22, A). Fusari shows irregular, large-bodied 
cells with many processes and neurites, when such are present, extending 
into layer 5. A bifurcate cell is figured by Mirto with its telodendrites 
in layer 3. My flounder impregnations produced neither of these types. 
I have spoken of layer 5 as the fillet layer because it is composed 
chiefly of fibres which pass backward and medianward, forming the so- 
called corona radiata of Gottsche, the lemniscus or fillet system. 
This layer is composed of cross and longitudinal fibres which, seen in 
tangential section, form a meshwork over the whole of the dorsal part 
of the tectum. In front of the optic ventricles bundles of fibres 
(Plate 5, Fig. 22, lmn.) can be followed from the axial part of the mid 
