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Cross section of a leaf, showing the breathing pores and intercellular spaces. The small dots are grains of chlorophyll.

Cross-section of a leaf

Cross section of a leaf, showing the breathing pores and intercellular spaces. The small dots are grains…

"Portion of the calcareous corallum of Millepora nodosa, showing the cyclical arrangement of the pores occupied by the "persons" or hydranths." — Encyclopedia Britannica, 1893

Millepora Nodosa

"Portion of the calcareous corallum of Millepora nodosa, showing the cyclical arrangement of the pores…

"Diagram of simple type of sponge. c, cloaca; ch, chambers, lined with flagellate entoderm; e.p., external pores; i.p., internal pores; mes., mesenchyma; o, osculum; r.c., radiating canals. In the adult sponge the canals and flagellate chambers become much more complex than figured here." — Galloway

Sponge

"Diagram of simple type of sponge. c, cloaca; ch, chambers, lined with flagellate entoderm; e.p., external…

An illustration of the lower portion of a sponge. O, OS, and M are illustrations of sponge eggs magnified forty times. The sponges or poriferans (from Latin porus "pore" and ferre "to bear") are animals of the phylum Porifera. Their bodies consist of an outer thin layer of cells, the pinacoderm and an inner mass of cells and skeletal elements, the choanoderm. Sponges do not have nervous, digestive or circulatory systems. Instead most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes, and the shapes of their bodies are adapted to maximize the efficiency of the water flow.

Lower Section of Sponge

An illustration of the lower portion of a sponge. O, OS, and M are illustrations of sponge eggs magnified…

An illustration of the upper portion of a sponge: p, Pore; s, Subdermal cavity; c1, chief fiver of the skeleton; c2, connecting film. The sponges or poriferans (from Latin porus "pore" and ferre "to bear") are animals of the phylum Porifera. Their bodies consist of an outer thin layer of cells, the pinacoderm and an inner mass of cells and skeletal elements, the choanoderm. Sponges do not have nervous, digestive or circulatory systems. Instead most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes, and the shapes of their bodies are adapted to maximize the efficiency of the water flow.

Upper Section of Sponge

An illustration of the upper portion of a sponge: p, Pore; s, Subdermal cavity; c1, chief fiver of the…