Abdomen of Hexapods

The abdomen constitutes the caudal tagma in the hexapods and is usually larger than the other two, the head and the thorax. This region is also referred to as a visceral area because it houses the visceral organs. Its form can vary depending on the group, and even on the species. The maximum number of observed segments is 11, although certain authorities consider a twelfth segment that in fact corresponds to a telsonic caudal region. In general, the number of segments decreases from the preimaginal phases to the adult stage, especially in those holometabolous insects in which the last segments of the adults are formed from imaginal discs during pupation. In the groups considered most primitive, the number of abdominal segments is usually greater, as occurs in the Protura with 11 segments (Figs. 2–5). An exception is the Collembola, which only possess six. In addition, it is necessary to keep in mind that, in certain cases, the total number of visible segments does not coincide with...