The quinoidal secretion, secreted by holocrine action from most gland cells (no cytoplasmic inclusions), of Orthocricus mboreus may ooze out or be sprayed over 30 cm. A thick gland intima and basement membrane protects internal organs.
The gland grades into a neck leading to an external orifice. An ejaculatory duct, its lumen closed by cuticular spring action, is formed by invagination of the neck. Part of the duct forms a tongue, which can independently unpIug the orifice. Retractor muscles open the ejaculatory duct, secretion flows in from the gland, and the part of the duct nearest the gland closes. Sequential relaxation of the rest of the retractor muscles build up fluid pressure, which results in a spray when the orifice is unplugged.
A ligament opposes the pull of the retractor muscles. Opening both duct and orifice results in secretion ooze. No intrinsic gland muscles were found. Intersegmental muscles may produce hemolyinph fluid pressure on the gland, thereby contributing to secretion ooze. Illustrations are presented. A table comparing the two basic types of millipede repugnatorial glands (spirobolid and polydesmid), on the levels of structure, histology, secretion, chemistry and function is presented. The polydesmid type (2-chambered) probably evolved from the spirobolid type (1-chambered). The secretion of one type would not work in the other type of apparatus. A second table correlates the secretion and ejection mechanism of 23 species of millipeds with their phylogenetic position in the class Diplopoda.