jacket cells (MESO: Orthonectida) The ciliated somatoderm; the number of body rings and their arrangement is of taxo-nomic importance.
jaculatory duct A region of the vas deferens through which sperm is emitted. see ejaculatory duct.
Johnston's organ (ARTHRO: Insecta) A chordotonal organ located in the second segment of the antenna and functioning in sound perception, flight speed indicator or water wave perception.
joint n. [L. jungere, to join] An articulation of two successive segments or parts.
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