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An extensive group of worms which have the body covered externally with vibrating cilia. It includes the Rhabdocoela and Dendrocoela. Formerly, the nemerteans were also included in this group.

One of the Turbellaria. Also used adjectively.

A group of Turbellaria in which there is no anal aperture.

A division of the Turbellaria in which the digestive cavity gives off lateral branches, which are often divided into smaller branchlets.

An organ in which the ova are developed in certain Turbellaria.

Any species of turbellarian worms belonging to Planaria, and many allied genera. The body is usually flat, thin, and smooth. Some species, in warm countries, are terrestrial.

One of the Planarida, or Dendrocoela; any turbellarian worm. -- Pla*na"ri*an, a.

A division of Turbellaria; the Dendrocoela.

A class of helminthes including the cestodes, or tapeworms, the trematodes, and the turbellarians. Called also flatworms.

A division of Turbellaria including those that have an intestine terminating posteriorly.

One of the peculiar rodlike corpuscles found in the integument of certain Turbellaria. They are filled with a soft granular substance.

A minute smooth rodlike or fusiform structure found in the tissues of many Turbellaria.

A suborder of Turbellaria including those that have a simple cylindrical, or saclike, stomach, without an intestine.

taining a minute rodlike structure which may be expelled. Such cells are found in certain Turbellaria.

A gland secreting the yolk of the eggs in trematodes, turbellarians, and some other helminths.

Any one of numerous species of small Turbellaria belonging to Vortex and allied genera. See Illustration in Appendix. Vortex atom (Chem.), a hypothetical ring-shaped mass of elementary matter in continuous vortical motion. It is conveniently regarded in certain mathematical speculations as the typical form and structur…

hids. -- Yolk gland (Zoöl.), a special organ which secretes the yolk of the eggs in many turbellarians, and in some other invertebrates. See Illust. of Hermaphrodite in Appendix. -- Yolk sack (Anat.), the umbilical vesicle. See under Unbilical.