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DR. H. W. HUBRECHT. 
the ganglion cells of the brain. It there appears to terminate 
blindly (PI. XXIII, fig. 3.) In all other respects the structure 
of the brain and nervous system closely agrees with C. annu- 
lata, 
A further degree of complication is attained in Polia, 
where the brain no longer lies immediately under the epi- 
derm, but is separated from it by intervening muscular tissue. 
Exteriorly the ciliated transverse grooves, with numerous 
small transverse furrows perpendicular to it, have very much 
the appearance of the grooves in Carinella inexpectata. 
Sections show that here the ciliated duct traverses the 
muscular tissue as well, enters between the nerve-cells of the 
brain, at the same time making a double bend (PL XXIII, 
fig. 4), and finally terminates in what appears to be a 
more or less swollen enlargement. Another complication 
has taken place, in so far as the brain is no longer a simple 
enlargement of the lateral trunks, but is split up into lobes, 
two dorsal ones and two ventral ones. Moreover, the dorsal 
lobes are separated into a larger anterior and a smaller pos- 
terior portion, applied to the former as a sort of cap. That 
such a separation exists is rarely visible by transparency ; it 
can only be clearly made out in horizontal sections. Only 
into this third portion of the brain, in this posterior dorsal 
lobe, the ciliated canal communicating with the exterior 
penetrates. In its turn this posterior cerebral lobe is capped 
over postero-medially by a layer of larger cells with distinct 
nuclei, which in their appearance strongly resemble the cells 
belonging to the coating of the oesophagus, which cells lie 
in their immediate vicinity in the same section. The situa- 
tion of this layer of cells is indicated by a paler tint in 
PI. XXIII, fig. 4. Further down we shall mention the 
authoPs views respecting the morphological significance of 
this group of cells. 
In all the Schizonemertini the external appearance of 
the apparatus is considerably different, in so far as there is 
no more any transverse furrrow or small opening of the 
ciliated canal, but two deep longitudinal slits on each side 
of the head, situated between the mouth and the tip of the 
snout. These slits penetrate deeply into the muscular 
tissue of the head, and in the bottom of them the lobes of 
the ganglion stand out more or less freely, only protected 
by a very thin layer of tissue. Their internal surface is 
covered by numerous and long cilia, and in their postero- 
medial portion they are continued into the ciliated canal 
which here penetrates into the third (posterior) ganglionic 
lobe. The author regards the cephalic slits in this suborder 
