. Animal biology. Zoology; Biology. SPONGES 135 through foraminal openings or tubules, or by rupture of the shells, and develop into new sponges (Fig. 56). Sexual reproduction also occurs, both egg cells and sperm cells being formed in the same animal. These sex cells lie in the jelly-like middle layer where fertiUzation takes place. An embryo is formed which escapes through the wall of the body and becomes a free-swimming ciUated larva. This later settles down and develops into a sponge. 159. Uses of Sponges.—The cleaned skeletons of those sponges which are composed entirely of spongin are fa
. Animal biology. Zoology; Biology. SPONGES 135 through foraminal openings or tubules, or by rupture of the shells, and develop into new sponges (Fig. 56). Sexual reproduction also occurs, both egg cells and sperm cells being formed in the same animal. These sex cells lie in the jelly-like middle layer where fertiUzation takes place. An embryo is formed which escapes through the wall of the body and becomes a free-swimming ciUated larva. This later settles down and develops into a sponge. 159. Uses of Sponges.—The cleaned skeletons of those sponges which are composed entirely of spongin are familiar because of their many domestic uses. Among these are bath sponges and the surgeons' sponges used to take up blood and other fluids in surgical operations. Though today artificial sponges are made which in many cases take the place of natural ones, there is still a large market for the latter. 160. Cultivation of Sponges.—The best commercial fibrous sponges come from the coast of the Mediterranean Sea, from the shores of Florida and the West Indies, and from Australia. They are gathered by means of long-handled hooks, by dredging, or by divers. They are then allowed to decay, are washed, dried, bleached more or less, and sent to market. Sponge culture is now carried on in several localities but most suc- cessfully in Italy and Florida. Commercial sponges do not flourish where the water is cold. The place selected for this purpose must have a clean bottom and must be exposed to currents which bring an abundant supply of well-aerated water and food. Specimens of the variety of sponge to be cultivated are secured, cut into small pieces approximately one inch square, and fastened either to stakes or to sunken cement plates. From these pieces grow complete sponges which are ready for the market in a few years, the time depending upon the character of the sponge grown and the conditions. When the sponge is gathered, the part that remains after most of it is cut away will co
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