File:The American Museum journal (c1900-(1918)) (17537302554).jpg

Title: The American Museum journal
Identifier: americanmuseumjo06amer (find matches)
Year: c1900-(1918) (c190s)
Authors: American Museum of Natural History
Subjects: Natural history
Publisher: New York : American Museum of Natural History
Contributing Library: American Museum of Natural History Library
Digitizing Sponsor: Biodiversity Heritage Library

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A GUIDE TO THE SPONGES 223 (See Fig. i.). This sponge is typically vase-like in external form. The circular opening at the top of the vase is known as the osciilmn (osc.) in spite of the fact that it is excretory and has neither structurally nor functionally the characteristics of a mouth. The walls of the vase are perforated with numerous regularly arranged openings or pores (p.) which open directly into the hollow interior of the sponge—called the paragastric or atrial cavity (air.). The walls are made up of three layers: ist, the ectoderm, or outer layer; 2d, the endoderm, or inner layer; 3d, the mesoderm, or middle layer. The ectoderm (ect.) is a thin layer of cells, generally arranged in mosaic form and known as "pavement cells." In the case of this species, however, the walls of the cells have disappeared and left the protoplasmic cell-contents continuous over the entire surface of the animal. Such a layer is called a syncytium. The endoderm (end.) lines the paragastric cavity and is made up of a layer of peculiar and characteristic cells called "collared cells, " or choanocytes (c/io.),foimd nowhere else among many-celled animals. They are so called from a collar-like rim around the outer edge of the cell out of which extends a long whip-like
Text Appearing After Image:
FIQ. 8.—SECTION THROUGH SPONGE WALL ect., ectoderm ; mes., mesoderm ; end., endoderm ; c/w., choanocytes or "collared cells; _/?a., flagellum. filament or flagellum (fla.). The continuous vibration of these flagella produces a current by means of which the sea-water, with its multitude of tiny animal and plant forms, is sucked in through the pores. The organisms are then seized upon by the

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