136 WILLIAM BLAXLAND BENHAM. 
regular intervals. The cells constituting a ridge are very 
long, narrow, and ciliated, containing a few granules (fig. 25, 
c.). These cells are much narrower at their inner extremities 
than at their free surfaces, so that they have a fan-shaped 
arrangement. 
The crypts alternating with the folds, have at the bottom a 
group of gland-cells, rather broader at their fixed ends than at 
their free surfaces, so that such a group of cells has somewhat 
the shape of a flask (gl.). The contents of these cells stain 
much more deeply than do those of the ridge-cells, and are 
much more finely granular. 
Among the bases of the cells are small patches of a finely 
granular, unstained substance, which I take to be nervous. 
The stomach is more or less completely surrounded by a 
plexus of sinuses of the vascular system. 
The intestine, or, as Caldwell calls it, the second stomach, 
is much narrower than the stomach. The epithelium consists 
simply of closely pressed granular columnar, ciliated cells. It 
is relatively short and soon passes into the rectum. 
The rectum is triangular in section throughout the greater 
part of its extent; its epithelium is not ciliated. 
The rectum is suspended to the body wall in a double way. 
It has its own “‘ rectal mesentery,” passing from one angle to 
the middle line of the body wall, almost exactly opposite to the 
cesophageal mesentery. Its second attachment is by means of 
the left lateral mesentery, against which one side of the rectum 
is fixed. The rectum passes outside the septum, at the oral 
region of the body, and lies immediately below the body 
wall (fig. 23), which it pushes outwards to form the rectal 
ridge. It then curves round to the dorsal surface, and opens 
by the anus, which is situated about the centre of the area 
enclosed by the tentacular crown, and very close to the gap in 
the inner series of tentacles. 
The Body-cavity.—The cavity in which the alimentary 
canal and blood-vessels lie is, as Caldwell (5) has shown, 
5 “Blastopore, mesoderm, and metameric segmentation,” ‘Quart. Journ. 
Micr. Sci.,’ 1885, 
