Il8 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



open into the anterior end of the broad, muscular cloaca. The 

 intestine is supported by three mesenteries, attached to the cor- 

 responding interradii. Thus the proximal section is attached 

 along the greater part of the length of the mid-dorsal interradius, 

 the second section to the left dorsal interradius, and the last 

 section to the right ventral interradius, as shown in Fig. 20. 

 In its total length the intestine describes a partial spiral turn 

 around the main axis of the body, as is easily seen by the position 

 of the attachment of the mesenteries. 



The mesentery attaching the third section to the right ventral 

 interradius is shown on Plate XXX.* 



Calcareous Ring. — Surrounding the anterior end of the 

 esophagus, and forming a support for the oral tentacles, is a 

 broad calcareous ring, consisting of five radial and five inter- 

 radial plates. The radial plates are notched anteriorly for the 

 passage of the radial nerve and have two long posterior projec- 

 tions, while the interradial plates are much simpler. 



Cloaca. — The cloaca serves not only for the discharge of 

 waste substances from the alimentary canal, but also has a most 

 important respiratory function as described below. It is in 

 sharp contrast with the extremely thin walled intestine in that 

 it is provided with very powerful circular and radiating muscles. 

 The former surround the cloaca closely, while the latter branch 

 out radially and pass directly through the coelom in all directions 

 to connect the cloaca with the adjacent body walls (Plate XXX). 

 The contraction of these radiating muscles causes the cloaca to 

 open widely, while the circular muscles serve to close it. When 

 the cloaca is opened, water rushes in from the outside through the 

 cloaca! aperture, and is thus forced up into the respiratory trees. 



The cloacal opening is supported by a narrow ring of cal- 

 careous plates, with five posterior projections, termed " anal 



* Since the animal is represented as opened along the ventral side, the organs on 

 the left side of the body are seen on the right-hand side of the figure. The fact 

 that the mesentery attaching the posterior portion of the intestine to the Tight ven- 

 tral interradius appears on the right-hand side of the figure shows that the cut has 

 heen made along the animal's right ventral interradius, between the mesentery and 

 the right ventral radius. The radius which extends along the median' axis of the 

 figure is therefore the left dorsal, while the right dorsal and right ventral are seen 

 on the left-hand side, and the left ventral and ventral on the right-hand side of the 

 figure (compare Fig. 20). 



