105 
one would expect, seeing that it is connected with the 
general activity of the organism, and the Plaice is sluggish 
in habits. : 
The mid-brain is represented on the dorsal surface on 
each side by the tectum opticum (optic lobe). These are 
very large bodies almost spherical in shape, and charac- 
terised in dead and preserved specimens, and doubtless in 
life also, by a deep furrow, which extends backwards in a 
curve from the anterior margin of each lobe for about half 
its antero-posterior diameter. 
As is usual in Teleosts, the “tween-brain hardly 
appears at all on the dorsal surface of the brain, being 
excluded from it by the meeting of the two striata and 
optic lobes. However, a small portion of its membranous 
roof is visible, and from this there is seen emerging by 
the triangular space formed immediately in front of the 
median apposition of the two optic lobes, the extremely 
fine pineal tube. In sections it is seen to arise as an 
evagination of the roof of the third ventricle almost 
behind the ganglia habenule and in front of the posterior 
commissure. It then passes forwards over the pallium of 
the left striatum and swells into the large pineal gland 
lying on the pallium near the anterior extremity of the 
left striatum. By pressing apart the optic lobes there 
may be seen immediately in front of the exit of the pineal 
tube the ganglia habenule and the plaited choroid roof of 
the third ventricle. 
In a well-preserved brain the membranous pallium of 
the fore-brain is very obvious. It is a large oval sheet, 
with its long axis at right-angles to that of the brain, and 
almost equal to that of the optic lobes. It is a very thin 
membrane, and appears thicker than it really is on account 
of the coagulated cerebro-spinal fluid in the ventricle. 
The corpora striata are also visible through the pallium. 
