362 THE ORIGIN OF VERTEBRATES 
of the nerve-fibres turn towards the flat, uppermost side, where the 
sense-organ is situated. Between the nerve-fibres (n.) and the chi- 
tinous surface containing the special sense-tubes masses of cells (gi.) 
are seen, as in Fig. 146, apparently nerve.cells, which form a broad 
border between the nerve-tibres and the pigmented chitinogenous 
Fic. 147.—SEcTION PARALLEL TO 
THE SURFACE OF FLABELLUM, 
SHOWING THE Porous TERMI- 
NATIONS OF THE SENSE-ORGANS 
AND THE ARRANGEMENT OF THE 
CANALICULI ROUND THEM, 
oe 
ae ‘ ‘ 
bi‘n gl pec 
Fic. 146.—SEcTION THROUGH FLABELLUM. 
ch., chitinous layers; s.0., sense-organs; sp., 
spike-organ; p., pigment layer; gl., ganglion 
cell layer; 62. and 2., blood-spaces and nerves. 
layer (p.). On the opposite side, nothing of the sort intervenes 
between the pigmented layer and the blood-spaces and nerve-fibres 
which constitute the central mass of the flabellum. 
At present I am inclined to look upon this mass of cells as 
constituting a large ganglion, which extends over the whole length 
aud breadth of the upper surface of the flabellum. At the same 
