242 SELIG HECHT 
the branchial sac are rapidly lashed to the tips of the papillae 
by their ventral cilia. Here they are caught by the mucus, and 
incorporated into the thread of food which is passing across the 
branchial sac. This cord of mucus and food is transported by 
the papillae. Waves of contraction bring two rows of papillae 
together, and by the action of the cilia the food cord is passed 
from one row to the next, until it reaches the oesophagus. 
Fig. 4 Papilla of the branchial sac. A, median section; B, section at the base 
of the papilla. 
The mechanism for these papillary movements is probably 
local, because touching a papilla with a glass rod causes a con- 
traction to appear. This would indicate that the waves are the 
result of a series of stimulations of the papillae by the contact 
of the food mass. 
The food as it enters the oesophagus is in the shape of a cord, 
and in this manner it is passed along the digestive tube. With 
the food also goes the mucus. Although the food is digested 
and absorbed, the mucus is probably not affected at all. When 
