CHORD ATA 441 



along the dorsal middle line of the branchial sac. In Ciona 

 the dorsal lamina is divided up into a number of languets, 

 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. 



Cio'/ia 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 suhneural 

 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 



