78 
height of which varies considerably. In the anterior por- 
tion of the stomach these folds are very little higher than 
the general line, but as they pass posteriorly they increase 
considerably, diminishing again in the intestine as they 
approach the rectum. The greatest height of the folds 
is reached in the portion of the intestine passing through 
the genital segment. In the intestine and posterior por- 
tion of the stomach there are a number of glandular cells, 
usually at the apices of the longitudinal folds, the contents 
of which stain deeply with eosin. In many of these the 
cell contents have disappeared, leaving a clear space, 
only the cell wall remaining. 
The wall of the stomach and intestine is marked by a 
series of transverse constrictions, giving it a crenate 
appearance, which is easily seen in the hving animal. In 
the hving animal an intermittent movement of the intes- 
tine and stomach is kept up. The action is wave-like, 
starting at one end, and passing to the other. After con- 
tinuing in one direction for a time, it reverses and passes 
the opposite way. There is no valve between the stomach 
and intestine, and when the peristaltic motion is reversed 
the fluid in the intestine is sent back into the stomach 
again. The only portions of the alimentary canal that 
can be closed are the esophagus and anal end of the 
rectum. The former is controlled by two longitudinal 
muscles which compress it, the latter by a number of 
muscles passing obliquely to the body-wall at the sides of 
the abdomen. The fluids contained in the alimentary 
canal are usually colourless, but occasionally when taken 
direct from the fish and placed under the microscope, a 
reddish tint may be detected at the posterior end of the 
cesophagus. 
In connection with the alimentary canal there is a 
distinct paired digestive gland (Plate IL., fig. 3 and fig. 9). 
