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"Diagrammatic vertical section through disc and base of one of the arms of Antedon rosacea. The section is inter-radial on the left, radial on the right. t., Ciliated openings in body wall; h., sub-epithelial ambulacral nerve; l., water-vascular canal; k., tentacle; r., mouth; s., intestine; g., central plexus, with "chambered organ" at its base; f., coelom; R1.-R3., radial plates; Br., brachial plates; u., muscle; a., axial nerve-cord; d., central capsule; C.D., centro-dorsal plate; p., cirri; e., nerve branches from central capsule to cirri." -Thomson, 1916

A. Rosacea Arm

"Diagrammatic vertical section through disc and base of one of the arms of Antedon rosacea. The section…

"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…

"Mesoderm formed by pouches from entoderm after gastrulation. A and B, early and later stages in formation of mesoderm and coelom. a, primitive gut; bp., blastopore; coe, body cavity, formed from pockets of the archenteron; ec., ectoderm; en., entoderm; m., mesoderm; m.so, body-wall mesoderm; m.sp., visceral mesoderm; s.c., segmentation cavity." -Galloway, 1915

Mesoderm Forming

"Mesoderm formed by pouches from entoderm after gastrulation. A and B, early and later stages in formation…

"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…