WILLIAMS: MIGRATION OF EYE IN PSEUDOPLEURONECTES. Al 
Passing from.without inward, the tectal layers are as follows: 
(1) A thin outer layer, composed principally of nerve fibrillations 
with a few nerve cells. In this layer the ependymal fibrillations end. 
A corresponding layer is recognized by writers on the finer anatomy of 
the tectum in the bony fishes, from Stieda (’67) onwards, except by 
Fusari (’87, 96) and Van Gehuchten (95). Fusari (’87) described a 
layer of vascular connective tissue beneath the pia, and later (96) his 
first layer of the tectum was made to embrace this vascular layer and 
the optic-fibre layer. 
(2) The layer of the medullated optic fibres. This is the continua- 
tion of the optic tract and is recognized as a separate layer by all writers 
on the tectum. 
(3) <A layer of optic fibrillations. This is not made a distinct layer 
by Stieda ('67), but Mayser (’81) and nearly all writers since his time 
have emphasized its presence. — 
(4) A spindle-cell layer. 
(5) The fillet layer, composed of longitudinal fibres and cross com- 
missural fibres. Stieda considered the fibres, which here run in two 
directions, as two layers. OC. L. Herrick (’91-92) describes a layer of 
commissural fibres beneath the fillet connecting the two optic lobes. 
(6) The “gray” layer. 
(7) The reticulate and ependymal layer. Some authors consider 
that this is composed of two distinct layers. The reticulate portion 
is not described at all by Neumayer (’95), Van Gehuchten (’95) nor 
Edinger (96). 
Mirto (’96) based his division of the tectum into layers on the shapes 
of the cells which he was able to demonstrate by the Golgi method. 
Following Cajal’s work on the tectum of birds, he describes fourteen 
layers. 
The degeneration methods did not yield much of importance in my 
hands, although the flounder, owing to its habit of protruding the eyes, 
is a favorable fish on which to operate. The animals, even the very 
small metamorphosed fishes, stand the shock of the removal of the eye 
well and bleed very little from the operation. The specimens tried by 
the Marchi method were very brittle, and demonstrated but one point 
clearly, that the sixth (nerve-cell) layer was reduced. Fusari (’96), who 
used the Weigert-Pal staining method on a Cyprinoid, concluded that 
all the tractus fibres degenerated when the eye was removed. Krause 
(98), after the Marchi treatment of fish from which the eyes had been 
removed, found that about one-tenth of the tract — mostly distributed 
