CHORDATA 441 
along the dorsal middle line of the branchial sac. In Ciona 
the dorsal lamina is divided up into a number of langquets, 
or tongue-like processes, which hang into the lumen of the 
sac (Fig. 254). One of these is given off at the level of each 
transverse vessel, and in this and some other respects they 
resemble the finger-like processes borne on the longitudinal 
bars. The dorsal lamina extends to the end of the branchial 
sac, and terminates close to the mouth of the oesophagus. 
Ciona lives upon minute organisms, etc., which float into 
the branchial sac with the water which is continually stream- 
ing through the body. These small particles become entangled 
in strands of mucus, and are directed to the dorsal lamina by 
the action of the cilia borne by the peripharyngeal groove 
and the endostyle or hypopharyngeal groove; the languets of 
the dorsal lamina, or epipharyngeal band, guide the food into 
the entrance of the oesophagus. The mucus which serves to 
entangle the food particles is probably partly secreted by the 
glandular cells of the hypopharyngeal groove, but probably 
also to a great extent by a gland which is situated under the 
central nerve ganglion. 
This glandular structure, usually known as the subnewral 
gland, is a compact body with few ramifications; its duct 
opens by a flattened mouth, which sometimes is folded in the 
most complicated fashion, but in Ciona is curved into a simple 
horse-shoe, situated dorsally near the posterior margin of the 
prebranchial zone. This gland has been regarded by some 
writers as homologous with the hypophysis cerebri of the 
Vertebrate brain. Some authorities have regarded this gland 
as a renal organ, but its function is more probably to secrete 
the mucus in which the food particles become entangled. 
The mouth of the oesophagus is an oval slit situated at 
the dorsal side of the branchial sac close to the end of the 
dorsal lamina, it leads into a short transparent tube, the oeso- 
phagus, which soon expands into the spherical stomach. There 
are no muscle fibres in the wall of the oesophagus, nor indeed 
in the whole length of the alimentary canal, except in the 
rectum; the food is propelled onward by means of the cilia 
which line the digestive tract. The stomach is large, and its 
posterior half is covered by the follicles of the testis; it leads 
