s 
ECHINUS. 309 
teeth lie. The included space forms part of the coelom, 
and is the peripharyngeal sinus. It is, however, completely 
shut off from the general coelomic cavity. 
The pharynx is five-rayed (Pl. IV., fig. 31), and each 
ray is attached by a pair of bands of connective tissue to 
the inner edges of the lateral faces of the adjacent alveolus. 
The pharynx passes into the oesophagus (Pl. IIL., fig. 23; 
Pl. V., fig. 37, @.), which ascends from the. lantern to 
the apex of the test. Turning downwards again, the 
cesophagus passes into the first or inferior spiral of the 
intestine (Pl. V., fig. 37, wf.s.), the commencement of 
which is marked by a sac-like swelling, and a consider- 
able increase in the diameter of the gut. The inferior 
spiral makes a complete circuit of the test, running in 
eracefully undulating folds through radius III. to IV., V., 
I., and IJ. into interradius 2. Here the intestine turns 
upon itself to form the superior spiral (swp.s.), which runs 
through radius II. to I., V., and IV. Thence, but with 
slightly reduced diameter, it turns again towards the apex 
ofthe test to form the rectum (Pl. III., fig. 23; Pl. V., 
fig. 37, rec.), which runs obliquely across interradius 3 to 
the anus, the opening of which is very small when com- 
pared with the diameter of the rectum. Mesenteric 
strands attach both spirals to the inner surface of the 
test, and separate from the coelomic cavity a small space 
which surrounds the anal end of the rectum, and forms 
the perianal sinus. Near the point where the cesophagus 
passes into the inferior spiral, an accessory or co-lateral 
intestine, the siphon (Pl. V., fig. 37, sz.), branches off 
from the intestine, along the inner (axial) side of which 
it runs to re-enter the main tube at or near the end of 
the spiral. Both coils of the intestine are extensively 
sacculated. 
In a transverse section of the cesophagus (PI. IV., fig. 32) 
