Other editions of book Elements Of Biology: A Practical Text-book Correlating Botany, Zoölogy, And Human Physiology

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1907 edition. Excerpt: ...SPONGES Grantia, a limy spinge, on the shell of a mussel. From photograph loaned by American Museum of Natural History. Limy Sponge (Grantia). The sponge is t he simplest of all Metazoa. One of the commonest forms is Grantia, a tiny urn-shaped object found in salt water attached to piles or stones. It is abundant in Long Island Sound. For this exercise have small vials containing specimens of Grantia preserved in formol or alcohol. The body is attached at one end. What do you find at the opposite end? Label the hole the oscuhtm. Tins leads into a cavity called the cloaca. The wall of the 0 body is pierced by a number of tiny holes or pores which communicate with the cloaca. The shape of the sponge is maintained by a skeleton composed of many tiny pieces or spicules of carbonate of lime. Notice; the edge of the osculum. Make a drawing of the Grantia twice natural size, showing all the above structures.' An examination with the microscope shows the pores of the sponge to be lined with ciliated cells. These, by means of movements of the cilia, set up a current of water toward the cloaca. This current bears food particles, tiny plants and animals, which are seized and digested by the ciliated cells. These cells seemingly pass on the food to the other cells of the body. The middle layer 1 See Hunter and Valentine, Manual, page 159. XV. CCELENTERATES Diagram of a simple sponge; t, inhalant opening; o, exhalant opening or onculum. Here the skeleton Some of the rarest Venus's flower basket: a sponge with a glassy skeleton. ectoderm; the inner layer, developed from the inner layer of the gastrula, the endoderm. A middle structureless layer, called the mesoglea, is also found. In higher animals this layer (called mesoderm),gives rise to muscles and parts...

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