198 SEGMENTED WORMS OR ANNELIDA. 



internal papillae with chitinous tips. The protrusion is due 

 to the pressure of the coelomic 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 

 median-ventral ciliated groove. (4) The intestinal, region is 

 much folded, " in a concertina-like manner," by the caudal 



e.bn 



FlG. 88. — Cross-section of Arenicola. — After Cosmovici. 



E., Epidermis ; cm., circular muscles ; Lm., longitudinal muscles ; 

 b.c, body cavity; gl., gill; s., set*; n.p., nephridial pore; 

 a,br., afferent branchial; e.&r., efferent branchial; n., ventral 

 nerve-cord, with blood vessels above ; d.v., dorsal vessel ; /.z»., 

 lateral vessel ; s.t.v., sub-intestinal vessels ; z/.v., ventral vessel ; 



£■■, gut- 

 septa, and is full of sand, from which the nutritive matter 

 has been absorbed. The anus is at the very end. 



Body cavity. — This is spacious, except in the tail 

 region, and contains a viscous ccelomic 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 

 third diaphragm the gut swings freely until the beginning 

 of the tail region, in which there are many septa. 



