ClipArt ETC
"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):…

"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…

"Diagrams to illustrate the development of one of the simpler types of sponge: I, the egg; 2, section of 16- to 32-celled stage; 3, section of later stage, a ciliated larva (blastula); 4, gastrula; 5, section through older larva which has become attached by the end containing the blastopore. New openings break through by the coalescence and perforation of the ectoderm and entoderm, and and a form results... a, archenteron; bl., blastopore; ec., ectoderm; en., entoderm; mes., mesenchyma; s, segmentation cavity." -Galloway, 1915

Simple Sponge Development

"Diagrams to illustrate the development of one of the simpler types of sponge: I, the egg; 2, section…