. Elements of zoölogy : a textbook. Zoology. Magnified portion of Pearl-shell. Magnified portion of Pinna. Magnified portion of Terebratula. not red. Their circulatory system consists of a heart, arteries and veins, and venous sinuses. Their respiratory organs are gills, or lung-like cavities. Their muscular system is well developed. Their nervous system is mainly FIG. 'Nervous System in the Molhiaca. a, ft, c, d, nerve-ganglions. The principal center of the nervous system is in the form of a ring surrounding the gullut. in the form of a ring which surrounds the oesophagus or throat, fro
. Elements of zoölogy : a textbook. Zoology. Magnified portion of Pearl-shell. Magnified portion of Pinna. Magnified portion of Terebratula. not red. Their circulatory system consists of a heart, arteries and veins, and venous sinuses. Their respiratory organs are gills, or lung-like cavities. Their muscular system is well developed. Their nervous system is mainly FIG. 'Nervous System in the Molhiaca. a, ft, c, d, nerve-ganglions. The principal center of the nervous system is in the form of a ring surrounding the gullut. in the form of a ring which surrounds the oesophagus or throat, from which nervous filaments radiate and con- nect with other nervous ganglia in other parts of the body. As to reproduction, most kinds of mollusks increase by means of eggs. Some kinds, as the River-Snails (Paludina), etc., are called viviparous, because they re- tain the eggs in the oviduct till after they are hatched, and the young have attained a considerable size. Some kinds of tunicate mollusks increase by Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Tenney, Sanborn, 1827-1877. New York : Scribner
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