"Cross-section of Arenicola. E., Epidermis; c.m., circular muscles; l.m., longitudinal muscles; b.c., body cavity; gl., gill; s., setae; n.p., nephridial pore; a.br., afferent branchial; e.br., efferent branchial; n., ventral nerve-cord, with blood vessels above; d.v., dorsal vessel; l.v., lateral vessel; s.i.v., sub-intestinal vessels; v.v., ventral vessel; g., gut." -Thomson, 1916

Arenicola

"Cross-section of Arenicola. E., Epidermis; c.m., circular muscles; l.m., longitudinal muscles; b.c.,…