This diagram shows a fresh-water annelid. a, appendages; br., brain; d, dissepiments; i, intestine; m, mouth; nph, nephridium; oe, aesophagus; p, pavilion, line with ciliated entoderm; ph., pharynx; pr., processes from the anal segment; z, zone immediately in front of the anal segment where new segments are continually being formed; z’, the zone of fission or budding. This takes place in the middle of a segment. The anterior half-segment of z’ will produce a region like z for the anterior half of the worm.
Thomas Walton Galloway, Zoology A Text-Book For Secondary Schools, Normal Schools and Colleges (Philadelphia: P. Plakiston's Son & Co., 1913) 220