GEROULD : CAUDINA. 149 
The cloaca is much dilated anteriorly, in the region where the 
respiratory trees branch off from it on either side; from this point 
backward to the anus it gradually diminishes in caliber. Numerous 
strands consisting of muscle fibers and connective tissue attach the 
cloaca to the body-wall. 
The line of attachment of the mesentery which supports the 
stomach and the small intestine in Caudina is remarkable only for 
the fact, that it is closely approximated to the longitudinal muscles 
alongside of which it runs, a condition which has been noted by 
Jaeg 
rer (33) in various forms of Holothuriidae and by Semper (768) 
in Chirodota. The mesentery itself is an unbroken sheet, which 
may be described under the two divisions called by Ludwig (89-92) 
the dorsal and the left. The dorsal division is attached to the right 
side of the dorsal interradius. At the bend in the small intestine 
the line of attachment of the mesenteries turns to the left side of the 
body and runs forward in the left-dorsal interradius as far as the end 
of the small intestine, being closely approximated to the left-dorsal 
radial muscles. This part of the mesentery is the /e/7 division 
of Ludwig. From this point the line of attachment of the mesen- 
tery bends sharply to the left and erosses the left-ventral and median- 
ventral radii into the right-ventral interradius, where near the 
anterior end of the small intestine it abruptly terminates; the third 
or right division of the mesentery, which, as is well known, is 
attached along the right-ventral interradius, is therefore not repre- 
sented in Caudina, except at the very beginning of the large 
intestine, 
Two sheets composed of separate muscular strands arise in the 
right-dorsal and left-dorsal interradii close to the right-ventral and 
left-ventral radial muscles. They serve to support the large intestine, 
Between the two layers of peritoneal epithelium of the mesenteries 
there are found, besides connective tissue, isolated muscle fibers 
running in various directions. 
2. HISTOLOGY. 
The alimentary tube throughout its whole extent consists of five 
layers of cells, which from without inward are (4) an outer layer 
of peritoneal epithelium, composed of ciliated cells, (H) a thin outer 
layer of conneetive tissue, (c) a layer of muscle fibers, which in turn 
consists of two layers, except in the pharynx, (4) a thick inner layer 
of connective tissue, and finally (e) the columnar epithelial lining of 
