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An illustration of a Acanthobdella, a member of the annelid family.

Acanthobdella

An illustration of a Acanthobdella, a member of the annelid family.

An illustration of a sectional view of a Acanthobdella, a member of the annelid family. "c, Coelom; c.ch, Coelomic epithelium (yellow cells); cg, glandular cells; cl, Muscle cells of lateral line; cp, Pigment cells; ep, Ectoderm; g, Nerve cord; m, Intestine; mc, Circular muscle; ml, Longitudinal muscle; vd, Dorsal vessel; ww, Ventral vessel." (Britannic, 1910)

Sectional View of Acanthobdella

An illustration of a sectional view of a Acanthobdella, a member of the annelid family. "c, Coelom;…

An illustration of a sectional view of a Acanthobdella, a member of the annelid family. "c, Coelom; c.ch, Coelomic epithelium (yellow cells); cg, glandular cells; cl, Muscle cells of lateral line; cp, Pigment cells; ep, Ectoderm; g, Nerve cord; m, Intestine; mc, Circular muscle; ml, Longitudinal muscle; vd, Dorsal vessel; ww, Ventral vessel; cn, nerve cord; nf, parts of nephridium; on, external opening of nephridium; ov, ova; t, testis." (Britannica, 1910)

Sectional View of Acanthobdella

An illustration of a sectional view of a Acanthobdella, a member of the annelid family. "c, Coelom;…

Amphitrite ornata.

Amphitrite Ornata

Amphitrite ornata.

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.

Annelid

This diagram shows a fresh-water annelid. a, appendages; br., brain; d, dissepiments; i, intestine;…

This diagram shows the longitudinal section of the anterior end of the annelid. A, sagittal section; B, frontal section to show anterior portion of nervous system. b, brain; co., nervous collar about the mouth; c.v., contractile blood vessels; d, dissepiment; d.m., dermo-muscular wall; d.v., dorsal blood vessel; m, mouth; n.c., nerve cells; n.f., nerve fibers; np., nephridia; p, prostomium; ph., pharynx; s, setae; sn., segmental nerves; v.g, ventral chain of fanglia; v.v., ventral blood vessel. Only a portion of the blood vascular system is shown, and this appears unsectioned in the figure.

Annelid

This diagram shows the longitudinal section of the anterior end of the annelid. A, sagittal section;…

This diagram shows a transverse section of dero. c., caelom; c.l., cells of the so-called "lateral line"; d.m., dermo-muscular wall including muscles and skin; d.v., dorsal blood vessel; ect, ectoderm; ent, entoderm; g, gut; g.f., giant nerve fibers; gl, glandular cells assisting in digestion; m.c., circular muscle fibers; m.l., longitudinal muscle fibers; n, nephridium; n.v., ventral nerve chain, made up of nerve cells and nerve fibers; s, setae; v.v., ventral blood vessel.

Annelid

This diagram shows a transverse section of dero. c., caelom; c.l., cells of the so-called "lateral line";…

Anterior part of the circulatory system of an annelid. The arrows indicate the direction of the flow. H, heart-like enlargement of the commissural vessel.

Circulatory System of an Annelid

Anterior part of the circulatory system of an annelid. The arrows indicate the direction of the flow.…

An illlustration of a dasychone infracta, a type of annelid. The annelids, collectively called Annelida (from Latin anellus "little ring"), are a large phylum of animals comprising the segmented worms, with about 15,000 modern species including the well-known earthworms and leeches.

Dasychone Infracta

An illlustration of a dasychone infracta, a type of annelid. The annelids, collectively called Annelida…

The earthworm works through the ground by insinuating its pointed head between the grains of dirt, (Hooker, 1882).

Earthworm

The earthworm works through the ground by insinuating its pointed head between the grains of dirt, (Hooker,…

The earthworm.

Earthworm

The earthworm.

"Anterior region of earthworm. Note the eight setae (s.) on each segment. R.S., Spots between 9-10, 10-11, indicate openings of receptacula seminis; Ovd., openings of oviducts on segment 14/ vd., openings of vasa deferentia on segment 13." -Thomson, 1916

Earthworm

"Anterior region of earthworm. Note the eight setae (s.) on each segment. R.S., Spots between 9-10,…

"Transverse section of earthworm. A., Cuticle; B., epidermis; C.M., circular muscles; L.M., longitudinal muscles; D., a seta; C., coelom; Y.C., yellow cells; F., typhlosole; V.V., supra-neural blood vessel; S.V., sub-neural vessel; D.V., dorsal vessel; P., peritoneum; E., cavity of gut; G., endodermic lining of gut; N., part of a nephridium; R., opening of a nephridium; I., the nerve-cord; J., a nerve given off; K., giant fibres in the nerve-cord." -Thomson, 1916

Earthworm

"Transverse section of earthworm. A., Cuticle; B., epidermis; C.M., circular muscles; L.M., longitudinal…

"Diagrams of various earthworms to illustrate external characters. A, B, C, anterior segments from the ventral surface; D, hinder end of the body of Urochaeta." (Britannica, 1910)

Earthworm

"Diagrams of various earthworms to illustrate external characters. A, B, C, anterior segments from the…

An illustration of the various types of earthworm setae. Seta (plural: setae) is a biological term derived from the Latin word for "bristle". It refers to a number of different bristle- or hair-like structures on living organisms. "A, penial seta of Perichaeta ceylonica; b, extremity of penial seta of Acanthodrilus; c, Seta of Urochaeta; d, Seta of Lumbricus; e, Seta of Criodrilus; f, g, Setae of Bohemilla comata; h, i, j, Setae of Psammoryctes barbatus." (Britannica, 1910)

Setae of Earthworm

An illustration of the various types of earthworm setae. Seta (plural: setae) is a biological term derived…

"Alimentary system of leech. m., Mouth; cr6., sixth crop-pocket; cr11., last crop-pocket; v., rectum; s., posterior sucker." -Thomson, 1916

Leech

"Alimentary system of leech. m., Mouth; cr6., sixth crop-pocket; cr11., last crop-pocket; v., rectum;…

"Dissection of leech. c.g., Cerebral ganglia; p., penis; s.v. is opposite the semminal vesicle; ov., ovary; ut., uterus; v.d., vas deferens; l.b.v., lateral blood vessel; T.4, fourth testis; n.v., nephridial vesicle; N.17, last nephridium; G.19, nineteenth pair of ganglia; n.c., nerve-cord." -Thomson, 1916

Leech Dissection

"Dissection of leech. c.g., Cerebral ganglia; p., penis; s.v. is opposite the semminal vesicle; ov.,…

"Transverse section of leech. c., Cuticle; e., epidermis; c.m., dermis and outer muscles (circular and oblique); l.m., longitudinal muscles (the peculiar connective tissue is hardly indicated); r.m., radial muscles; l.v., lateral blood vessel; d.s., dorsal sinus; v.s., ventral sinus enclosing nerve-cord (n.); g., median part of crop, with lateral pockets (p.); t., testis; f., nephridial funnels; v.d., vas deferens." -Thomson, 1916

Leech Section

"Transverse section of leech. c., Cuticle; e., epidermis; c.m., dermis and outer muscles (circular and…

"Head of Hirudo medicinalis, showing the three jaws (k); b, one of the jaws isolated, with the finely toothed free edge." -Parker, 1900

Medical Leech

"Head of Hirudo medicinalis, showing the three jaws (k); b, one of the jaws isolated, with the finely…

An illustration of the marine worm larva, Lopadorhymchus.

Lopadorhymchus

An illustration of the marine worm larva, Lopadorhymchus.

"Arenicola marina. Entire animal viewed slightly from left side. Note anterior mouth; setae on anterior region; setae and gills on median region; thinner tail region often longer than shown." -Thomson, 1916

Lugworm

"Arenicola marina. Entire animal viewed slightly from left side. Note anterior mouth; setae on anterior…

"Lumbricus agricola. A, entire specimen, lateral view; B, ventral view of anterior portion of the body, magnified. 1, 15, 33, first, fifteenth, and thirty-third segments. The black dots represent the setae." -Parker, 1900

Lumbricus Agricola

"Lumbricus agricola. A, entire specimen, lateral view; B, ventral view of anterior portion of the body,…

"Modes of forming mesoderm. A and B, special mesoblasts distinguishable early in egmentation (annelid): A, surface view from active pole; B, sectional view of same. ec, micromeres destined to form ectoderm; en, macromeres destined to form entoderm; m, primitive mesoblast which produces the mesoderm. C, amaeboid mesodermal cells (c) budding from entoderm into the segmentation cavity (s.c.), in an Echinoderm. a, archenteron." — Galloway

Mesoderm

"Modes of forming mesoderm. A and B, special mesoblasts distinguishable early in egmentation (annelid):…

"Free-living Polychaete (Nereis cultrifera)." -Thomson, 1916

Polychaete

"Free-living Polychaete (Nereis cultrifera)." -Thomson, 1916

"Elytrum of Polymoë, a polychaetous annelid, bearing fimbriae, viewed from above." -Whitney, 1911

Polymoë

"Elytrum of Polymoë, a polychaetous annelid, bearing fimbriae, viewed from above." -Whitney, 1911

Structure of the protonephridium (excretory organ) of a shark. Labels: Wtr, ciliated funnels; Ug, segmental duct.

Protonephridium of a Shark

Structure of the protonephridium (excretory organ) of a shark. Labels: Wtr, ciliated funnels; Ug, segmental…

Structure of the protonephridium (excretory organ) of an annelid. Labels: Wtr, ciliated funnels; Ds, dissepiments.

Protonephridium of an Annelid

Structure of the protonephridium (excretory organ) of an annelid. Labels: Wtr, ciliated funnels; Ds,…

"Esophageal Ring. Anterior end of nervous system of Polynoë, a polychaetous annelid, showing, a, cerebral ganglia, connected by the esophageal ring, b, with the ventral series of ganglia, c." -Whitney, 1911

Scale Worm Nervous System

"Esophageal Ring. Anterior end of nervous system of Polynoë, a polychaetous annelid, showing, a,…

Echiurus gaertneri is a species of spoon worm considered annelids, though they are not segmented.

Spoon Worm

Echiurus gaertneri is a species of spoon worm considered annelids, though they are not segmented.