ClipArt ETC
Diagrams of the body layers and cavities in A, coelenterates; B, flatworms; C, annelids; D, vertebrates. Labels: G, gastric cavity; g, cavity of the gonad; a, primary body cavity (blastocoele) filled with branched cells (mesenchyme); c, secondary body cavity (coelom); d, dorsal mesentery; m, mesenchyme filling space of original primary body cavity; n, nerve tube.

Body Layers and Cavities

Diagrams of the body layers and cavities in A, coelenterates; B, flatworms; C, annelids; D, vertebrates.…

"Development of excretory system of vertebrate. The primitive segments are not separated off from the lateral plate, and the pronephros (pn.) is seen arising from the lower part of the primitive segment. n.c., nerve cord; nch., notochord; pn., pronephros; g., gut; p.s., primitive segment; mes., mesonephric tubule; pn.d., pronephric duct; b.c., body cavity; ao., aorta; siv., sub-intestinal vein, with vessel to the aorta." -Thomson, 1916

Excretory System Stage 1

"Development of excretory system of vertebrate. The primitive segments are not separated off from the…

"Development of excretory system of vertebrate. The pronephros is completely separated off from the primitive segment and lateral plate. n.c., nerve cord; nch., notochord; pn., pronephros; g., gut; p.s., primitive segment; mes., mesonephric tubule; pn.d., pronephric duct; b.c., body cavity; ao., aorta; siv., sub-intestinal vein, with vessel to the aorta." -Thomson, 1916

Excretory System Stage 2

"Development of excretory system of vertebrate. The pronephros is completely separated off from the…

"The origin of the mesonephric tubules is seen. They arise from the upper part of the lateral plate, which is now completely separated from the primitive segment, and curving round the pronephric duct come to open into it. n.c., nerve cord; nch., notochord; pn., pronephros; g., gut; p.s., primitive segment; mes., mesonephric tubule; pn.d., pronephric duct; b.c., body cavity; ao., aorta; siv., sub-intestinal vein, with vessel to the aorta." -Thomson, 1916

Excretory System Stage 3

"The origin of the mesonephric tubules is seen. They arise from the upper part of the lateral plate,…

"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…