ORIGIN OF THE GULA IN INSECTS

Abstract

The primitive occipital foramen is oblique in most prognathous heads. The terminal regions of the postocciput, the tentorial pits, and the base of the submentum are all carried forward on the ventral side of the head, and the neck membrane extends into the space bounded by the postocciput and the submentum. Usually, however, this space is occupied instead by a sclerite known as the gula, which is continuous with the ventral portions of the postocciput and united, with or without a suture, with the base of the submentum.Evidence is adduced to show that the gula originated wholly or in large part as a sclerotization in the neck membrane which later united with the postocciput and submentum. In Anisolabis the origin is wholly cervical, the postgenae playing no active part, but in Anisamorpha and Diapheromera postoccipital lobes grow mesally and unite with the cervical sclerite to form the gula.