AMPHIOXUS LANCEOLATUS. 
383 
bar is not of a bifid or double character, but is a single hollow 
rod, which is continued directly from the mid-point of the 
upper chitinous arch. It does not at the lower end of the 
primary gill-slit come into contact with the chitinous lower 
arch, but simply joins the endostyle or median inferior area of 
the pharynx, the chitinous material ceasing at the point of 
junction. The general arrangement of the bars is shown 
in Muller’s original plates, and is so well known that I have 
not thought it necessary to figure it here. 
The primary bars and the tongue-bars differ in other respects 
besides the fact that the rod of the primary bar is essentially 
bifid and that of the tongue-bar a hollow single rod. A. 
Schneider and Langerhans have described the structure of 
these bars as seen in transverse sections ; but I think that the 
former has erred in assigning too many vascular passages to 
the bars, whilst the latter has assigned too few. My own 
conclusions are exhibited in the drawings given in PI. 
XXXYI B, figs. 1 and 2. 
Both bars are flattened like a lath, and are set with the nar- 
rowest diameter parallel to the long axis of the Ampliioxus. 
The atrial surface of the bars is clothed with the atrial epi- 
thelium ( atr . ep.), the cells of which are especially deep and 
large, whilst the brown pigment is limited to a strongly- 
marked group of cells on each side ( pig .). The inner face of 
the bars — that turned towards the lumen of the pharynx — is 
provided with a peculiar epithelium arranged in three rows 
( al ., am., ar.), the cells of which are very narrow and long, with 
elongate deeply-staining nuclei. These cells resemble those 
found in group al. and ar. of the endostylar epithelium (see 
fig. 9, PI. XXXYI B), and like them carry short cilia. 
The adjacent sides of the bars bounding the passage between 
neighbouring bars are lined with columnar cells, which carry 
very long cilia (col.). Below the outlines of these columnar 
cells an immense number of closely aggregated nuclei, which 
stain strongly with either hsematoxylin or carmine, are ob- 
served. The superficial series of these (n.) probably belong to 
the columnar cells. Whether the deeper nuclei (n'.) are all to 
