260 E. RAY LANKESTER. 
folds of the pharynx.—Stieda has figured these, but not 
quite correctly (figs. 3 and 4, Plate 1). They consist of what 
appear in transverse section as fibres passing horizontally 
from the uppermost bars of the pharynx to the wall of the 
atrial chamber. In reality they are membranous folds, ex- 
tending for some length along the bars to which they are 
attached. ‘They become more numerous as one advances 
from the posterior to the anterior region of the pharynx, and 
in conformity with a change in the shape of the cross-section 
of that organ and the disappearance of the testicular and 
ovarian pouches in the anterior region of the body, they 
become developed from all the bars of the lateral region of 
the pharynx. These folds may be in parts adherent to the 
lateral wall of the atrial chamber on each side, and are very 
possibly muscular. The folds are double, being in fact but 
flat sacs formed by the outgrowth of the atrial tunic and its 
subjacent fibrous layer on alternate chitinous bars. The 
‘bars which do not give rise to a fold are tubular ; those which 
do are solid. Each fold contains between its lamelle a 
lymph-space (part of the ceelom). The spaces between the 
double folds are open posteriorly to the atrial chamber, but 
the pigment of the atrial tunic does not completely line 
them, and on the median side they are, of course, widely 
open to the pharynx by the two long slits, one on each side, 
of a tubular pharyngeal bar which is devoid of a fold. I 
propose to call these structures respectively pharyngo- 
pleural septaor lymph-sacs,and pharyngo-pleural inter-spaces. 
Pigmented canals (vertebrate renal organs).—In examining 
transverse sections of Amphioxus, as we advance from behind 
forwards, we come to a part where the atrial chamber is 
occupied by the lateral generative pouches, by the ccecum but 
just given off, and by the so-called cesophagus. A few slices in 
front of this we get the first bars of the pharynx appearing, 
and then what might be mistaken for the first pharyngo- 
pleural septum is detected on each side, viz. a band running 
across from the dorsal region of the pharynx to join the body 
wall, and leaving a considerable space on each side of the sub- 
chordal attachment of the pharynx. A pair of vascular 
trunks lie in each of these spaces near the summit of the 
pharynx. The space on each side runs throughout the 
length of the pharynx. It is correctly marked as pleuro-peri- 
toneal cavity in Stieda’s Pl. I, figs 3 and 4. Posteriorly 
this space, which may be called the pharyngo-dorsal ccelom 
can be traced to complete separation from the alimentary 
canal existing only as a split in the double membrane which 
lines the epipleur, exactly like the neighbouring split in 
