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obligatory parthenogenesis      Parthenogenesis in which a species reproduces entirely without males.

oblongum cell                  (of hind wing). A cell located at the end of the medial bar and formed from rp-mp crossveins; occurs in most Archostemata, Adephaga and Myxophaga.

obtect                                                   With appendages lightly adpressed to the body.

occipital carina.                              A transverse carina in the occipital region, usually located at the point where the top of the head normally protrudes from the anterior edge of the pronotum.

occipital foramen                           An opening in the cranium through which nerve chords, the aorta, oesophagus, salivary ducts, and a pair of trachea enter or leave the neck.

occipital groove.                             Median longitudinal groove on the posterior part of the head, extending from the occipital foramen to some point on the vertex or frontal region; usually associated with an endocarina. See occipital line.

occipital line.                    Median longitudinal line or ridge on the posterior part of the head, extending from the occipital foramen to some point on the vertex or frontal region; usually associated with an endocarina. See occipital groove.

occipital region.                              The posteriormost area of the head capsule; not clearly distinguished from the vertex, which lies just in front of it.

occipital suture           Groove running around the posterior of the head in some insects, it separates the vertex from the occiput.

occiput            Hind most region on the top of the head.

ocellar bristles      Bristles around or between occelli in certain flies.

ocellar triangles   Area usually distinct from the rest of the head on which occelli of diptera are housed.

ocellus                 (pl. Ocelli). A simple eye located between or behind the compound eyes; there may be a single, median ocellus or a pair of them.

oligolectic                                                          Bees that gather pollen from only a few species of related flower. c.f. polylectic.

ommatidium                     (pl. Ommatidia). An element making up the compound eye and visible externally as an eye facet; consisting of an external cornea (sometimes projecting internally as a corneal exocone lens), a crystalline cone (in eucone eyes only), a clear zone and a rhabdome (Caveney 1986).

ootheca                                                               A body containing a cluster of eggs, especially in Blattodea and Mantodea. In several species of cockroach the right and the left glands produce different chemicals, which when mixed produce the tanned ootheca walls.

oviparity, oviparous                      The eggs hatch after being laid. Oviposition generally occurs soon after fetilization, but it may be delayed until embryonic development is more or less advanced. This is the common

method in most orders.

ovoviviparity, ovoviviporous                     The eggs are retained, usually in the vagina, until they hatch, and the young larvae then deposited; but the term is also used when hatching occurs immeadiately after deposition. The vaginal wall may be richly tracheated to provide for embryonic respiration, irrespective of whether eclosion takes place before of after deposition, and there is no physiological difference between these two conditions. Ovovivipary occurs in some species of most orders.