Rectal tracheal gills: lamelliform structures in the rectum of the nymphs of some Odonata, supplied with trachea and tracheoles and serving as respiratory organs.
Rectangular: in the form of a right or rectangle.
Rectangulate: forming or meeting in a right angle.
Rectigrade: larvae which, having sixteen feet, walk with a rectilinear body.
Rectilinear: in the form of a straight line.
Rectum: a chamber, variable in size and form, just within the anus, in which the excretions are formed or molded for expulsion from the body:= cloaca.
Rectus: right or straight.
Recumbent: lying down; reclining.
Recurrent: running backward: applied to nerves it = stomatogastric.
Recurrent nervure: in Hymenoptera (Nort.), is the medial cross vein (Comst.), from the point of branching to the junction.