Paired erectile plates (patagia) are borne on the prothorax in moths, while in moths, sawflies, wasps, bees and other insects there are small plates (tegulae) - see Fig.
The Viperidae alone have "erectile" fangs.
Although firmly anchylosed to the bone, the tooth, which when at rest is laid backwards, is erectile, - the bone itself being mobile and rotated round its transverse axis.
The mucous membrane is raised into a series of transverse folds or rugae, and between it and the muscular wall are plexuses of veins forming erectile tissue.
The penis is the intromittent organ of generation, and is made up of three cylinders of erectile tissue, covered by skin and subcutaneous tissue without fat.