Editing Scorpion (section)

===Mesosoma===

[[File:Vista ventral de un escorpión.jpg|thumb|upright|right<!--left-->|Ventral view: the [[pectines]] have a comblike structure in an inverted V shape.]]

The mesosoma or preabdomen is the broad part of the opisthosoma.{{sfn|Polis|1990|pp=10–11}} In the early stages of embryonic development the mesosoma consist of eight segments, but the first segment disappear before birth, so the mesosoma in scorpions actually consist of segments 2-8.<ref>{{Cite journal|title=The ultrastructure of book lung development in the bark scorpion Centruroides gracilis (Scorpiones: Buthidae) - PMC|year=2011 |pmc=3199777 |last1=Farley |first1=R. D. |journal=Frontiers in Zoology |volume=8 |page=18 |doi=10.1186/1742-9994-8-18 |pmid=21791110 |doi-access=free }}</ref><ref>{{Cite web|url=http://www.sharmalabuw.org/uploads/1/3/6/1/13619635/schwager_et_al._2015.pdf|title=Chelicerata - Prashant P. Sharma}}</ref><ref>{{Cite web|url=http://www.science.marshall.edu/fet/euscorpius/p2011_120.pdf|title=Euscorpius - Marshall University}}</ref> These [[anterior]] seven [[somite]]s (segments) of the opisthosoma are each covered [[Anatomical terms of location|dorsally]] by a sclerotized plate called the [[tergite]]. [[Ventral]]ly, somites 3 to 7 are armored with matching plates called [[sternites]]. The ventral side of somite 1 has a pair of genital [[Operculum (animal)|opercula]] covering the [[gonopore]]. Sternite 2 forms the basal plate bearing the [[pectines]],{{sfn|Polis|1990|pp=13–14}} which function as sensory organs.<ref name="Knowlton Gaffin 2011">{{cite journal |last1=Knowlton |first1=Elizabeth D. |last2=Gaffin |first2=Douglas D. |title=Functionally Redundant Peg Sensilla on the Scorpion Pecten |journal=Journal of Comparative Physiology A |publisher=Springer |volume=197 |issue=9 |year=2011 |issn=0340-7594 |doi=10.1007/s00359-011-0650-9 |pages=895–902|pmid=21647695 |s2cid=22123929 }}</ref>

The next four somites, 3 to 6, all bear pairs of [[Spiracle (arthropods)|spiracles]]. They serve as openings for the scorpion's respiratory organs, known as [[book lungs]]. The spiracle openings may be slits, circular, elliptical or oval according to the species.{{sfn|Polis|1990|p=15}}<ref name="Wanninger 2015">{{cite book |last=Wanninger |first=Andreas |title=Evolutionary Developmental Biology of Invertebrates 3: Ecdysozoa I: Non-Tetraconata |url=https://books.google.com/books?id=rxZcCgAAQBAJ&pg=PA105 |year=2015 |publisher=Springer |isbn=978-3-7091-1865-8 |page=105 |access-date=11 September 2017 |archive-date=5 August 2020 |archive-url=https://web.archive.org/web/20200805003251/https://books.google.com/books?id=rxZcCgAAQBAJ&pg=PA105 |url-status=live }}</ref> There are thus four pairs of book lungs; each consists of some 140 to 150 thin [[lamella (surface anatomy)|lamellae]] filled with air inside a pulmonary chamber, connected on the ventral side to an atrial chamber which opens into a spiracle. Bristles hold the lamellae apart. A muscle opens the spiracle and widens the atrial chamber; dorsoventral muscles contract to compress the pulmonary chamber, forcing air out, and relax to allow the chamber to refill.{{sfn|Polis|1990|pp=42–44}} The 7th and last somite does not bear appendages or any other significant external structures.{{sfn|Polis|1990|p=15}}

The mesosoma contains the heart or "dorsal vessel" which is the center of the scorpion's [[open circulatory system]]. The heart is continuous with a deep arterial system which spreads throughout the body. Sinuses return deoxygenated blood ([[hemolymph]]) to the heart; the blood is re-oxygenated by cardiac pores. The mesosoma also contains the reproductive system. The female [[gonad]]s are made of three or four tubes that run parallel to each other and are connected by two to four transverse [[anastomoses]]. These tubes are the sites for both [[oocyte]] formation and embryonic development. They connect to two [[oviduct]]s which connect to a single atrium leading to the genital orifice.{{sfn|Stockmann|2015|pp=45–46}} Males have two gonads made of two cylindrical tubes with a ladder-like configuration; they contain cysts which produce [[spermatozoa]]. Both tubes end in a [[spermiduct]], one on each side of the mesosoma. They connect to glandular symmetrical structures called paraxial organs, which end at the genital orifice. These secrete [[chitin]]-based structures which come together to form the [[spermatophore]].{{sfn|Stockmann|2015|p=47}}<ref>{{cite journal |last1=Lautié |first1=N. |last2=Soranzo |first2=L. |last3=Lajarille |first3=M.-E. |last4=Stockmann |first4=R. |year=2007 |title=Paraxial Organ of a Scorpion: Structural and Ultrastructural Studies of ''Euscorpius tergestinus'' Paraxial Organ (Scorpiones, Euscorpiidae) |journal=Invertebrate Reproduction & Development |volume=51 |issue=2 |pages=77–90 |doi=10.1080/07924259.2008.9652258 |s2cid=84763256 }}</ref>