Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] SPONGES 193 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 of other internal struc- tures. Other Sponges. — Sponges may be placed, according to the kind
Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] SPONGES 193 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 of other internal struc- tures. Other Sponges. — Sponges may be placed, according to the kind of skeleton they possess, in the following groups: (1) The limy sponges, in which the skeleton is composed of spicules of carbonate of lime. Grantia is an example. (2) The glassy sponges. is made of silica or glass. and most beautiful of all sponges belong in this class. The Venus's flower basket is the best known. (3) The horny fiber sponges. These, the sponges of commerce, have the skeleton com- posed of tough fibers of material somewhat like that of cow's horn. This fiber is elastic and has the power to absorb water. In a hving state, the horny fiber sponge is a dark-colored fleshy mass, usually found attached to rocks. The warm waters of the Mediter- ranean Sea and the West Indies furnish most of our sponges. The sponges are pulled up from their resting place on the bottom, either by means of long-handled rakes operated by men in boats, or are secured by divers. They are then spread out on the shore in the sun, and the living tissues allowed to decay; then after treatment con- sisting of beating, trimming, and bleaching, the bath sponge is ready for the market. Relation to Environment.— Sponges are found in both fresh . , „, r D .1, • ^,,+ and salt water.^ They are found A homy fiber sponge; , the mcurrent pores; 0, osculum. Notice that this sponge ^ Only one species of fresh water is made up of apparently several individuals. sponge, Spongilla, is known in this
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