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"Diagrams of stages in the metamorphosis of Polygordius, a primitive annelid. Ectoderm throughout is represented as nucleated without cell boundaries; the entoderm has the cell-boundaries shown, and the mesoderm is diagonally shaded. A, gastrula; B, same with blastopore closed; C and D represent formation of stomodaeum and proctodaeum from ectoderm; E, Trochosphere stage showing formation of segments in the posterior portion; F, adult (sagittal); G, adult (transverse). a, archenteron; bp., blostopore; br, brain; c, coelom; d, dorsal; di, dissepiments; m, mesenteron; pr., proctodaeum; s.c., segmentation cavity; st, stomodaeum; v.n., ventral nerve chain; z, zone of formation of nerve segments." -Galloway, 1915

Polygordius

"Diagrams of stages in the metamorphosis of Polygordius, a primitive annelid. Ectoderm throughout is…

This diagram shows a sagittal section of a Rotifer. b, brain; bl., excretory bladder; c, cloaca, the common opening of digestive and reproductive organs; co, caelom; e, eyespot; ex, excretory canal; f, flame cells; f.g., foot gland; ft., foot; g, gut; m, mouth; m.f., longitudinal muscle fibres; mx, mastax; o, ovary; pf., pharynx; s.g., salivary gland; t, tentacle; tr, trochus, or cilia-bearing disc.

Rotifer

This diagram shows a sagittal section of a Rotifer. b, brain; bl., excretory bladder; c, cloaca, the…

Horizontal section through the trunk at the level of the first lumbar vertebra showing descriptive terms. Labels: M.P., mesial plane; S, sagittal; C, coronal or frontal.

Horizontal Section Through the Trunk

Horizontal section through the trunk at the level of the first lumbar vertebra showing descriptive terms.…