382 
E. RAY LANKESTER. 
according to Schneider, with the dorso-pharyngeal coelom at 
the anterior extremity of the caecum through the coelomic 
spaces within the pharyngo-pleural pouches of the primary 
bars of the pharynx, which rest against and open into the 
blood-holding cavity which surrounds the coelom. I can 
confirm this observation from the study of transverse sections 
made by my pupil, Mr. Willey. 
The question as to how the blood which is brought by 
veins into the cardiac aorta or great contractile blood-channel 
underlying the hypopharyngeal ridge “ circulates,” or whether, 
indeed, it circulates at all, has not been, in my judgment, 
satisfactorily answered, and renewed investigations are needed. 
This is in part due to the difficulty of investigating the structure 
of the pharyngeal bars and of arriving at a certain conclusion 
as to what are real natural spaces and channels and what are 
artifacts. 
The structure of the pharyngeal bars is shown in PI. 
XXXVI B, figs. 1 and 2, which represent sections at right 
angles to the length of the bars. As is well known, from the 
observations of Muller and others, the bars are not all similar, 
but of two kinds, viz. (1) those which correspond to the 
division between primary gill-slits, the “ primary bars,” and 
(2) those which form by a growth downwards from the dorsal 
margin of a primary slit, dividing it into two secondary slits. 
These are in relation like the tongue of a Jew’s-harp, and may 
be called “ tongue-bars.” The development of these bars may 
be seen in any Amphioxus continually in progress in the 
posterior region of the pharynx. The chitin-like material 
which forms the skeleton of the pharynx is deposited in the 
form of rod-like tracts beneath the epithelium (in the cutis- 
layer) boundiug the margin of the gill-slits. Accordingly 
there is a double rod in each primary bar, one half corre- 
sponding to each of the adjacent gill-slits. At each end of 
the gill-slit this double rod bifurcates, and each half of the 
fork runs parallel with the arch-like boundary of the gill-slit, 
tending to meet the furcal half of the next double rod at the 
summit of the arch. On the other hand, the rod of the tongue- 
