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special organs in some insects and crustaceans.
(1) A part of the internal chitinous skeleton of an insect thorax, also known as apophysis. The furca projects into the body in the form of a furcate outgrowth (on the ventral side of the thoracic segments), to which muscle tendons are attached.
(2) A springing organ of insects of the order Collembola, also known as furcula. The furca consists of a pair of out-growths grown together at their base on the ventral side of the fourth abdominal segment. When at rest these outgrowths are folded under the abdomen and secured to a special outgrowth on the third abdominal segment. The furca can unfold downward and backward with force, and when it strikes the ground, it can propel the insect into the air.
(3) A pair of appendages at the end of the last abdominal segment in some crustaceans, such as copepods.