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"Gastrula of a Chalk-sponge (Olynthus). A, external view." -Whitney, 1911

Chalk Sponge Gastrula

"Gastrula of a Chalk-sponge (Olynthus). A, external view." -Whitney, 1911

"Gastrula of a Chalk-sponge (Olynthus). B, longitudinal section through the axis: g, primitive intestine; o, blastopore; i, inner cell-layer of the body-wall; e, outer cell-layer." -Whitney, 1911

Chalk Sponge Gastrula

"Gastrula of a Chalk-sponge (Olynthus). B, longitudinal section through the axis: g, primitive intestine;…

"Early stages in the development of Amphioxus. 1. Ovum with germinal vesicle; 2. four-cell stage; 3. external appearance of blastula; 4. blastula in section; 5. beginning of gastrula stage; 6. section of completed gastrula." -Thomson, 1916

Lancelet Stages

"Early stages in the development of Amphioxus. 1. Ovum with germinal vesicle; 2. four-cell stage; 3.…

"Diagrammatic representation of development of Oscarella lobularis. Bl., Free-swimming blastula with flagella; G., gastrula settled down. Next figure shows folding of inner layer (En.); Ec., outer layer. Lowest figure shows radial chambers (R.C.); Mesogloea (Mg.); inhalant pore (P.); exhalant osculum (O.)." -Thomson, 1916

O. Lobularis

"Diagrammatic representation of development of Oscarella lobularis. Bl., Free-swimming blastula with…

"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…

"Section of a sponge. Showing inhalant canals, flagellate chambers, a gastrula forming in the mesogloea, etc." -Thomson, 1916

Sponge Section

"Section of a sponge. Showing inhalant canals, flagellate chambers, a gastrula forming in the mesogloea,…

"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…

The sponge, a many celled animal, begins its life as a single-cell, the egg. After division of cells and formation of blastula, the young larva leaves the parent. The next transformation consists of a pushing in of one side. This depression deepens and gradually results in the formation of a two layered sac know as the gastrula.

Sponge Develoment

The sponge, a many celled animal, begins its life as a single-cell, the egg. After division of cells…