Shell-fish industries . thefilament. The functions performed by these complicated gillsare many. They are breathing organs, and were prob-ably developed originally for thatpurpose alone. Blood, that is con-tinually streaming through themany filaments, is brought so closeto the water surrounding the gillsthat oxygen borne by it enters thefluid by diffusion and is then car-ried to all parts of the body. Butit is necessary that water surround-ing the gills should frequently bechanged because its oxygen isquickly exhausted. In many aqua-tic animals the gills move back andforth to agitate the water
Shell-fish industries . thefilament. The functions performed by these complicated gillsare many. They are breathing organs, and were prob-ably developed originally for thatpurpose alone. Blood, that is con-tinually streaming through themany filaments, is brought so closeto the water surrounding the gillsthat oxygen borne by it enters thefluid by diffusion and is then car-ried to all parts of the body. Butit is necessary that water surround-ing the gills should frequently bechanged because its oxygen isquickly exhausted. In many aqua-tic animals the gills move back andforth to agitate the water, orspecial organs are developed todirect a current upon them. Herea very powerful current of themost effective sort is produced bythe gills themselves. The cilia lashin such a way as to drive waterbetween filaments on both sides of the gill into its inte-rior. The passageway is indicated by the arrows in thefigures of the oyster and scallop gills. The current doesnot pause here, but continues swiftly upward toward the. Fig. 9.—Transverse sec-tion of a single fila-ment of the gill ofPec ten designatedare : — f c, frontalcilia; fire,gland cells;.y c, straining cilia;and b, blood space. Anatomy of the Food Mollusks 37 base of the gill, where it enters a tube which is withoutobstructing interlamellar partitions, and leads backwardto the cloacal chamber. This has been described as aspace above the four gills and behind the main portionof the body. Into this cloaca all four gills continually pour theirstreams, which unite to form a powerful current thatleaves the body either directly between the unmodifiedmantle folds, or through the dorsal chamber of thesiphon tube. As a large amount of water is in this waybeing constantly forced out of the body, a correspond-ing volume is being drawn in. It enters directly be-tween the mantle folds into the gill chamber, or, in theclams, is drawn into it through the ventral tube of thesiphon. So rapid is the stream in all
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Keywords: ., bookcentury1900, bookdecade1910, bookpublishernewyo, bookyear1910
