a. Transparent spots or marks on the wings. b. In Orthoptera, a small membranous area at the base of an antennae of a cockroach. c. In Isoptera, a cavity on the head; a fontanel.d. The membranous base of the ommatidia at the junction with the optic nerve of a compound eye; a transparent ocellate spot in an eye. e. In male Odonata, the genital opening on the ventral surface of abdominal segment 11; see fontanelle.
4. (BRYOZOA: Gymnolaemata)
In Cheilostomata, an open space or mesh in reticulate zoaria.
5. (NEMATA)
a. In Secernentea, the thin membranous area surrounding or on either side of the vulva of a cyst forming nematode (Heterodera spp.). b. In some marine Adenophorea, the openings in subcuticular helmets through which sensory nerves pass; fenestrateadj., fenestration n.