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HAPLODRILI (so called by Lankester), often called Archiannelida (Hatschek), the name provisionally given to a number of
A, Polygordius neapolitanus. (From Fraipont.)
B, Transverse section of Polygordius. (From Fraipont.)
C, Trochophore of Polygordius. and D, later stage of the same, showing the development of the trunk. (From Hatschek.)
E, Dorsal view of Dinophilus taeniatus.
F, Male apparatus of the sa ne (From Harmer.)
a,	Anus.
ap, Apical organ.
c,	Coelom.
c.o, Ciliated pit.
c.t,	Cuticle.
d.v, Dorsal vessel.
e,	Eye.
ep, Epidermis.
g,f, Genital funnel.
h, "Head kidney," with second nephridium just below it.
i,	Intestine.
Lm, Longitudinal muscles.
m, Mouth.
m.o, Muscular pharyngeal organ. m.p, Male pore.
n, Nephridium.
o.m, Oblique muscles.
ov, Ovary.
p,	Penis.
pr, Prototroch.
pt, Prostomial tentacle.
sp, Sperm-sac.
spd, Sperm-duct.
si, Stomach.
t,	Testes.
tr, Trunk segment.
tt, Telotroch.
v.n, Ventral nerve cord.
v.v, Ventral vessel.
interesting lowly-organized marine worms, whose affinities are very doubtful (see CHAETOPODA). Polygordius and Protodrilus
Whatever may be the conclusion as to the position of Dinophilus and Histriodrilus, it seems only reasonable to suppose that Polygordius and Protodrilus, so far from representing a stage in the phylogeny of the Annelida before setae were developed, have lost the setae, which -are already in a reduced state in Saccocirrus.
AUTHORITIEs.—Hatschek, " Studien z. Entw. der Anneliden," Arb. Zool. Inst. Wien, vol. i., 1878; " Protodrilus," ibid. vol. iii. (1881); Fraipont, "Le Genre Polygordius," Fauna u. Flora d. Golfes v. Neapel., xiv., 1887; Weldon, " Dinophilus gigas," Quart. Journ. Micr. Sci. vol. xxvii., 1886; Harmer, " Dinophilus," Journ. Mar. Biol. N.S. vol. i., 1889; Schimkewitsch, " Entwickl. des Dinophilus," Zeit. f. wiss. Zool. vol. lix., 1895; Korschelt, " ~} V ber Bau u. Entw. des Dinophilus," Zeit. f. wiss. Zool. vol. xxxvii., 1882; Foettinger, " Histriobdella," Arch. Biol. vol. v., 1884; Goodrich, " On Saccocirrus," Quart. Journ. Micr. Sci. vol. xliv., 1901.	(E. S. G.)