ClipArt ETC
"Diagram of early segmentation stages in a Gasteropod. A, 2-celled stage; B, 4-celled; C, 8-celled; D, later stage, in section. ect., ectoderm cells (micromeres); ent., entoderm cells, macromeres; mes., mesoblasts, early put aside,--before gastrulation--to form the mesoderm; mi., micromeres; ma., macromeres." -Galloway, 1915

Gastropod Segmentation

"Diagram of early segmentation stages in a Gasteropod. A, 2-celled stage; B, 4-celled; C, 8-celled;…

"Gastrulation of an Ascidian. I. Vesicular Morula of an Ascidian flattened and about to undergo gastrulation. II. Gastrulation effected. fh, cavity of the morula, or blasto-invagination; ch, dd, large blastomeres of the hypoblast, inclosed in small blastomeres of the epiblast." -Whitney, 1911

Sea Squirt Gastrulation

"Gastrulation of an Ascidian. I. Vesicular Morula of an Ascidian flattened and about to undergo gastrulation.…