ch.i P . iv.] ENTERON OF CHORDATA. 139 



on the ventral surface of the body, not far from the 

 anterior end, is over-hung by a hood, and supported 

 by cartilaginous bars, which bear ciliated cirri, the 

 gill-like appearance of which gained for the animal 

 the misleading name of Branchiostoma. As these 

 cirri are moved by muscles they are enabled to direct 

 food to the mouth, and to serve as a filter against the 

 entrance of sand and other useless or dangerous 

 bodies. As in the rest of the lower Chordata, this 

 mouth serves as the orifice of entrance for the water 

 of respiration, which makes its way to the exterior 

 through numerous spaces in the wall cf the more an- 

 terior region of the digestive tract. The part of the 

 tract behind the gill chamber is of some width, and 

 gradually narrows as it approaches the amis, which 

 is situated on the ventral surface not far from the 

 hinder end of the body. At its anterior end it gives 

 off a forwardly directed short blind process, which is 

 known as the liver. As in the Kemertinea, the 

 enteric epithelium is ciliated. In the Uroclior- 

 data. a large part of the anterior region of the 

 enteron is again converted into a respiratory cham- 

 ber ; and it is the succeeding portion only that is 

 limited to the duties of a digestive apparatus. The 

 tube vaiies in width in different regions and is 

 ordinarily coiled on itself, so that the anal is not far 

 from the oral orifice ; the food passes into it along 

 a groove which lies on the ventral surface of the 

 respiratory chamber, the sides of which are ciliated, 

 and the cells of which secrete a mucous substance 

 which entangles the food and carries it into the 

 oesophagus. The anterior orifice of the oesophagus 

 is generally funnel-shaped, and provided with cilia ; 

 the succeeding portion has a diverticulum, which is 

 spoken of as the liver, and it may be further provided 

 with other glandular organs. In some cases the 

 digestive tube is coiled into a closely compacted 



