74 
GROliOK K. NI('IIOT-l,S. 
probably, tbo^massa fcerminale” of Sterzi (’07, p. 303). 
It, sooins probable that the terminal ping was, in life, inserted 
in tins gap. Owing to its shape (almost hour-glass in form 
in transverse sections) the central canal is, at a point just 
anteilor to the sinus terminal is, cut twice in sagittal 
sections, the upper and lower portions of the canal being 
separated by the bulging masses of the side walls. Eeissner’s 
fibre lies always in the lower canal (fig. 48, r.c.)} 
In older ammocoetes, however, the central canal has become 
considerably larger, and the fibre of Reissner may be much 
more readily traced. As it traverses the central canal it is 
seen to be joined at short intervals by cilia from tlie 
ependymal cells (fig. 5G). 'Phese attachments seem to be quite 
strong, for the fibre has deviated slightly from a straight line, 
and instead of running centrally along the canal has a gentle 
zig-zag course as though held firmly here and there. The 
jmrticular instance figured was that observed in the central 
canal iu the tail region of a 34 mm. ammocfcte, but such a 
condition of the fibre may be seen in well-preserved material 
of practically all larval forms, in which, of course, the fibre 
is still relatively slight. In still older specimens, where the 
fibre attains a greater size, it appears to follow a more nearly 
straight course at or near the centre of the canal. 
In a larva of 36 mm. the sinus terminalis lies imme- 
diately dorsal to the extremity of the notochord. It is here 
an ovoid space almost surrounded by the epend 3 'inal 
epithelium, which is, however, incomplete dorso-posteriorl}'. 
Into the gap thus left there is fitted a conical mass, the 
terminal plug (fig. 53, j>.), from the apex of which, project- 
ing antero-ventrally, Reissner’s fibre may be made out running 
forward. 
Another specimen, somewhat older (12 mm. in length), also 
shows Reissner’s fibre ending in a terminal plug (Fig. 51 , /.p.), 
which seems to be continuous with the mesenchymatous tissue 
which lies immediately behind the terminal neural pore. 
* Cf. the condition of the central canal of Myxine and Bdellostoina 
described below. 
