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Any contractile vessel of invertebrates which is not of the nature of a real heart, especially one of those pertaining to the excretory system.

continual regeneration of the epithelial cells of the body, or the regeneration of the contractile substance of muscle.

Capable of being retracted; retractile.

A division of marine gastropods having a retractile proboscis and three longitudinal rows of teeth on the radula. It includes many of the large ornamental shells, as the miters, murices, olives, purpuras, volutes, and whelks. See Illust. in Append.

n the back of the head or neck of a nudibranch or tectibranch mollusk. They are usually retractile, and often transversely furrowed or plicate, and are regarded as olfactory organs. Called also dorsal tentacles. See Illust. under Pygobranchia, and Opisthobranchia.

A suborder of leeches including those that have a protractile proboscis, without jaws. Clepsine is the type.

on of pectinibranchiate gastropods, having the head prolonged into a snout which is not retractile.

ves or other organs opening into the intercellular spaces, and usually bordered by two contractile cells.

The quality of being tractile; ductility. Derham.

a pellucid watery liquid, or some special chemical secretions of the cell protoplasm. Contractile vacuole. (Zoöl.) See under Contractile, and see Illusts. of Infusoria, and Lobosa. -- Food vacuole. (Zoöl.) See under Food, and see Illust. of Infusoria.

th a circle of vibrating cilia around the oral disk. Most of the species have slender, contractile stems, either simple or branched.