Stemmata: simple eyes or ocelli; q.v.
Stem-mother: in plant lice; that form hatching from the winter egg, which starts a series of agamic summer generations.
Stenocephalous: with a narrow, elongate head.
Stenorhynchan: narrow beaked or snouted.
Stenothorax: a supposed ring between pro- and meso-thorax.
Stercoral: relating or pertaining to excrement.
Sterile: not capable of reproducing its kind.
Sternal orifice: in Perlids; a peculiar slit on each side of the sternum, extending inward and ending blindly := furcal orifice.
Sternal spatula: = breast-bone; q.v.
Sternauli: the short and often obsolete furrows on either side of the mesosternum in Hymenoptera.