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"Development of Polygordius. a., Mother sperm cell; b., c., sperm morulae; d., spermatosoa. 1. Ovum with large nucleus; 2. two-cell stage; 3. four-cell stage; 4. blastosphere; 5. gastrula; ac., archenteron; 6. closure of gastrula mouth or blastopore; 7. formation of stomodaeum (st.), and proctodaeum (pr.), which invaginate to meet archenteron (ac.); 8. complete gut formed; 9. elongation of larva; ap. sp., posterior segments; 11. form of adult Polygordius." -Thomson, 1916

Polygordius

"Development of Polygordius. a., Mother sperm cell; b., c., sperm morulae; d., spermatosoa. 1. Ovum…

"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…