AMPHIOXUS LANCEOLATUS. 
387 
of the adjacent anterior and posterior halves of the furcal 
extremities of the rods of the primary gill-bars. 
Whilst the furcal ends of the rods of the primary bars of 
the pharynx penetrate thus deeply below the endostyle, the 
rods of the tongue-bars are shown, by the drawings referred to, 
only to reach the margin of the endostylar tract. A large 
coelomic space exists beneath the endostylar chitinous plates, 
and around the furcal ends of the primary rods. This space 
is seen by following the sections to communicate freely with 
two structures of the pharyngeal bars, viz. (a) with the soft- 
walled pharyngo-pleural fold of the primary bars, and (6) 
with the cavity of the hollow chitinous rod of the tongue-bars. 
The contractile endostylar artery or cardiac aorta is seen in 
the sections either in the middle line or a little to the right or 
to the left. A large branch is given off from it to each 
primary bar, but the sections have not enabled me to trace 
the vessel actually into the bar or along its length. No 
vessel is given off to the tongue-bars. 
I have not observed in sections of the endostylar region the 
muscular tissue which Schneider has described as existing 
there, and I doubt the correctness of his observation. 
The structure of the deep part of the rods of the primary 
bars, where their bifurcate extremities lie below the chitinous 
plates of the endostyle, is remarkable. The substance of the 
rods consists of a reticular tissue with scattered nuclei, and the 
chitinous matter appears to be superficially deposited around 
this axis (see figs. 4 — 9, Plate XXXVI jB). It is necessary to 
bear in mind that in speaking of the rods of the pharyngeal 
skeleton as “ chitinous , ” one is using that term without strict 
justification, in order to indicate not the specific chemical sub- 
stance “ chitin,” but a certain density and horn-like character in 
a structureless skeletal deposit. The “ chitinoid” substance of 
the pharyngeal bars and of the endostylar plates of Amphioxus 
appears to be a special form of the subepidermic lamina of the 
connective tissue, which is seen everywhere affording firm 
support to the columnar cells of the body-surface. It is to be 
regarded as a product of the connective tissue, and it is there-. 
