384 
E. KAY LANKESTEK. 
be reckoned to epithelium seems doubtful. A clear median 
space or line exists (sept.) which must consist of a connective 
tissue, and the deepest nuclei would in all probability be 
referable to that tissue (and therefore to mesoblast). 
The chitin-like rod lies near the atrial border of the primary 
bar (PI. XXXVI .6, fig. 1 Rod), and similarly in the tongue- 
bar (fig. 2 Rod). In both the rod is grooved on its inner 
(pharyngeal) face, so as to form a small channel, which is 
probably occupied by a blood-vessel marked Bl. vess. in the 
figures. This is the only space which I can find in the 
transverse section of the bars, excepting the larger space 
marked coelom in the figures, and the fissure more or less 
complete of the double rod of the primary bars ( fiss . in the 
figures), and an occasional (by no means constant) minute 
defect in the rod of the tongue-bar (sc. in the figures). The 
blood-vessels which are given off right and left from the great 
artery of the endostyle (see figs. 4 to 9, PI. XXXVI i?) pass 
into the bases of the primary bars, where their rods bifurcate, 
and are possibly and probably continued up the primary bars 
in the channel marked Bl. vess. in fig. 1. It is, however, to 
be noted that this channel is very narrow relatively to the 
vessels given off from the median ventral artery of the 
endostyle, and that the tongue-bars certainly receive no such 
branches from the endostylar artery, although the channel 
exists in them also. Schneider figures a vessel passing from 
the dorsal end of each bar — both tongue-bars and primary 
bars — into the dorsal aorta ; and possibly a communication 
exists between the vessel of each primary bar and that of the 
adjacent tongue-bars by means of the transverse junctions 
which occur at intervals along the length of the bars. I have 
not been able to satisfy myself as to the existence of the 
communications with the dorsal aorta described by Schneider, 
nor as to the existence of vessels in the transverse junctions. 
At the same time it seems very probable that both exist, and 
a little further investigation may enable us to recognise them 
in sections. 
Between the chitinous rod and the atrial epithelium of the 
