2I 4 



PH YL UM 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 



FIG. 103. Cross-section of Arenicola. After Cosmovici. 



7i ., Epidermis ; c.in., circular muscles ; /.;//., longitudinal muscles ; 

 /'.<r., body cavity; gl., gill; s., setae ; ./., nephridial pore; 

 a.br., afferent branchial ; c.br., efferent branchial ; n., ventral 

 nerve-cord, with blood vessels above ; d.v., dorsal vessel ; /.?>., 

 lateral vessel ; s.Lz*., sub-intestinal vessels ; v.v., ventral vessel ; 



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 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 

 third diaphragm the gut swings freely until the beginning 

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



