226 PHYLUM ANNELIDA. 
Food canal.—(1) The buccal cavity is protrusible as a 
“proboscis” or introvert, which grips the sand, and bears 
internal papilla with chitinous tips. The protrusion is due 
to the pressure of the ccelomic fluid, while special muscles 
bring about retraction. (2) The gullet has smooth walls, 
and bears a posterior pair of glands, which secrete a 
yellowish fluid, probably digestive. (3) The gastric region, 
from the heart to the twelfth or thirteenth notopodium, is 
covered with yellow cells and many blood vessels, and has a 
Fic. 118.—Cross-section ot Avenzcola.—After Cosmovici. 
E., Epidermis; c.#z., circular muscles ; ¢.7., longitudinal muscles ; 
b.c., body cavity; g/., gill; s., seta; 2.f., nephridial pore; 
a.6x., afferent branchial; ¢.47., efferent branchial; ., ventral 
nerve-cord, with blood vessels above; d@.z., dorsal vessel; /.v., 
lateral vessel; s.z.v., sub-intestinal vessels; v.v., ventral vessel ; 
Sy Bute 
median-ventral ciliated groove. (4) The intestinal region is 
much folded, ‘“‘in a concertina-like manner,” by the caudal 
septa, and is full of sand, from which the nutritive matter 
has been absorbed. The anus is at the very end. 
Body cavity.x—This is spacious, except in the tail 
region, and contains a viscous coelomic fluid. Anteriorly 
there are three transverse, partly muscular, septa or 
diaphragms which moor the gullet. The first of these 
diaphragms bears a pair of small pouches. Behind the 
