Mesothorax
The mesothorax (derived from the Greek mesos for "middle" and thorax for "breastplate") is the second and therefore middle segment of the insect's chest area ( thorax ) . It is followed by the metathorax , and in front of it is the prothorax . Each of the insects' thorax segments has a pair of legs . In the mesothorax, these are the middle legs. In addition, the mesothorax carries the first pair of wings (forewings) in flying insects . However, the wings can also be missing.
In winged insects, the two posterior thorax segments are often combined to form the pterothorax (from the Greek pteron : "wing, feather, fin"). The parts of the exoskeleton in the section of the mesothorax, which are separated from one another by sutures (sutures) , commonly referred to as sclerites , each have a special name; In general, the sclerites of the pterothorax have grown together to form a closed, immovably connected structure, so that the wings and the driving flight muscles are given sufficient stability. The front part of the trunk (prothorax) can also be connected, but is usually offset by an articulated, movable connection; In this case, the fuselage is somewhat mobile, for example the parts can be rotated against each other to a certain extent.
As with other sections, the upwardly limiting sclerite tergum , the abdominal sternum , usually located between the legs, and the lateral plates to the right and left of the body are called pleura , in this case mesotergum, mesosternum, mesopleura. Separate sections of it, delimited by seams, are respectively called tergites, sternites and pleurites (but the terms tergum / tergite etc. are often used synonymously , in somewhat vague usage ). For the tergite, the synonymous expression Nota (singular: Notum ) is common, in the case of the mesothorax it is mesonotum. When viewed from above, the mesotergum (or mesonotum) is usually divided into three consecutive sections, which are referred to as the mesopräskutum, Mesoskutum and Mesoskutellum. Their size can vary greatly depending on the order of the insect, but the mesoskutum is usually much larger than the others. In winged insects, the mesoskutellum is often the only openly visible sclerite of the Pterothrax when the wings lie on their back in a resting position, which is why it is usually simply called the scutellum in many insect orders, for example the beetles .
The mesosternum is usually an undivided plate. There are various transformations. In the hymenoptera, the mesosternum is shifted inside the body and is mostly invisible, the visible lower end of the mesothorax is formed here by the side sections or pleura. The pleuras of the trunk section are usually structured in a more complicated way, since this is where the leg joint sits with the base member of the insect leg, the coxa or hip. Usually a conspicuous suture, the pleural groove, which runs between the wing joint and the deflection of the coxa, divides the section into two parts. The, mostly larger, section in front of it is called the episternum, the, mostly smaller, behind it is called the epimeron, here thus the mesepisternum and mesepimeron. The smaller sclerites have different names depending on their order. Parts of the coxae can also be immovably fused with the trunk section and thus simulate trunk sclerite.
The size of the two segments of the pterothorax against each other mostly correlates with the wing size. In flying insects, in which the forewings are noticeably larger and contribute most to flight, the mesothorax is almost always much larger than the metathorax.
supporting documents
- ↑ a b c Metathorax. In: Herder-Lexikon der Biologie. CD-ROM, Spektrum Akademischer Verlag, Heidelberg 2003, ISBN 3-8274-0354-5 .
- ^ A b David H. Headrick & Gordon Gordh: Anatomy: Head, Thorax, Abdomen, and Genitalia. In Vincent H. Resh & Ring T. Cardé (editors): Encyclopedia of Insects. Academic Press (Elsevier), Amsterdam, etc., 2003. ISBN 0-12-586990-8
- ^ Goulet H & Huber JT: Hymenoptera of the world: An identification guide to families. Center for Land and Biological Resources Research, Ottawa 1993, ISBN 0660149338