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Eggs are meroblastic, telolecital and do partial crushing.

Eggs are meroblastic, telolecital and do partial crushing.

This segment does not correspond to the segment because it is located behind the anus, in the caudal process (cancer telson).

The whole body of scorpions is covered with chitinous shell, which is the product of the selection of the underlying hypothermic layer. There are cephalothorax, which covers the cephalothorax on the dorsal side, then in the area of ​​the preabdomen, respectively, the number of segments 7 of the dorsal and abdominal shields connected by a soft membrane, and finally in the area of the postabdomen 5 closed dense chitinous rings connected thin skin.

Limbs

On the abdominal side of the body, six pairs of limbs are attached to the cephalothorax, of which 2 front pairs play the role of the jaw organs, while the other four pairs are used for walking. The first pair of limbs is located above the mouth and in its position corresponds to the tentacles of other Arthropoda, and in physiological function – the jaws, and therefore are called tentacles or chelicera; they look like small 3-membered horizontal claws and are used to grind food.

The second pair of 6-membered limbs with their main joints plays the role of jaws and in appearance resembles legs, ending with large claws, with which scorpions grab the victim. In other arachnids, they have the appearance of tentacles – and therefore are called jaw tentacles,

Intestine

The intestine consists of three sections: anterior, midgut and hindgut; the mouth is located on the abdominal side and leads to the muscular pharynx, which acts as a pump that passes into the esophagus (oesophagus) is initially very narrow, which then expands and receives the excretory ducts of the two large salivary glands. The esophagus passes into the midgut, in which in the area of ​​the preabdomen opens with 5 pairs of excretory ducts a large multilobed liver, which performs all the gaps between other organs.

The midgut gradually passes into the short hindgut, which is opened by powder to the outside in the last segment on the abdominal side. The nervous system consists of the supraglottic ganglion, peripharyngeal commissure and abdominal nerve chain.

From the suprapharyngeal bilobed ganglion nerves to the eyes and tentacles. In the abdominal nerve chain there are one large subpharyngeal ganglion, which occurred by merging all the thoracic ganglia, and seven abdominal, ie three pre-abdominal and 4 postabdominal (located in the tail) ganglia.

Sense organs

The eyes are best developed and researched. Scorpios have 3-6 pairs of eyes on the upper topics for a personal narrative side of the cephalothorax, one pair of which is different in size and more complex structure, is located in the middle of the cephalothorax and is called the middle eyes, while others are located in lateral groups near the anterior edge and are called lateral eyes.

The latter consists only of a cuticular lens and one layer of cells – large terminal nerve cells with a lateral column and a special highly refracting light ball and smaller, indifferent or supporting cells. The middle eyes have one large cuticular lens, and under it a separate unpigmented layer of the vitreous, separated by a membrane from the adjacent layer of terminal nerve cells, or retina; in the retina, every five cells are interconnected into one group – the so-called retinula, isolated from neighboring retinula by a layer of pigment; each retinal cell secretes on its inner surface a vitreous column, or rhabdomer, which connects with adjacent 4 rhabdomers in one rod, or rhabdom (rhabdom).

These eyes of scorpions represent as though transition from a simple eye to the faceted arthropods. S. still have very peculiar sense organs – so called. comb-shaped bodies (pectines), having the form of the plate bordered on one party by teeth and in the general reminding a crest; they are located on the abdominal side of the second abdominal segment, near the genitals are supplied in abundance with nerve branches. They are likely to serve as tangential organs, and their close position to the genitals suggests that they are the excitatory organs in intercourse.

Circulatory organs

The circulatory system does not represent a closed system, being in communication with or gaps in areas of the body cavity.

The heart is located on the dorsal side in the preabdominal and lies between the blades of the liver, lying in a special shell that separates the pericardial cavity filled with blood. It looks like a long tube divided into eight chambers. Each chamber is supplied with one pair of slit-shaped openings (ostia) with valves; at both ends the heart continues into two main arteries: anterior, heading to the head (aorta cephalica), and posterior, going to the postabdomen (arteria posterior); in addition, another pair of lateral arteries departs from each chamber. Two branches of the main artery form a vascular ring around the esophagus, from which extends back a large artery that lies above the nerve chain.

At reduction of heart blood arrives in front and back aorta and from them in small vessels and gathers at last in two longitudinal abdominal sinuses, goes then to pulmonary leaves, is oxidized there and by means of special channels returns to pericardial cavity (pericardium), and then through cracks. with diastole back to the heart.

The respiratory organs are contained in the pre-abdomen and are represented by the lungs, which have the form of 8 large air sacs that go into the body cavity and open to the outside through narrow oblique or slit openings, so called. stigmata, or breather. The latter are located in pairs on the abdominal side of the preabdomen, on the sides in 3-6 segments.

Lung bags

Pulmonary sacs of scorpions represent the changed gill-bearing extremities which appear in the place of the rudiments of abdominal extremities existing in an embryonic stage of development. The excretory organs are still little studied and consist of two long and thin vessels (malpighian vessels) that open into the posterior part of the hindgut.

Lymphatic glands have recently been found by Kovalevsky in scorpions and are presented as one pair of saccular or several irregularly shaped glands adjacent to the nervous system and containing amoeboid (phagocytic) cells that greedily eat various foreign substances introduced into the body cavity. carmine, iron, anthrax bacteria, etc.)

Genitals

All scorpions are heterosexual, and in appearance differ only in size. The male genitalia consists of one pair of testes, each of which is formed of two longitudinal thin tubes that lie in the preabdominal between the blades of the liver and interconnected by transverse channels.

Each pair of tubes at the anterior end of the body passes into the excretory canal (vas deferens), which are interconnected in the midline and open on the abdominal side of the body in the first abdominal segment to the outside. In the excretory ducts open on each side of one long and short sac, the first of which is the seminal vesicle (vesicula seminalis).

The female genitals are located in the same place as the male, and consist of two longitudinal tubes, arcuate at the rear end of the third, middle, and, in addition, connected to it by four transverse channels. This system of tubes together forms the ovaries (ovarii).

At the anterior end of both lateral tubes depart oviducts (oviducti), dilated spindle-shaped and forming seed receivers (receptacula seminis); the two fallopian tubes are connected into one unpaired excretory duct, which opens outward on the abdominal side of the body in the first abdominal segment. The female, as well as a man’s genital opening is covered with two plates – the genital cover representing the changed abdominal extremities and the corresponding (on position) genital or gill plate or swordtails of Xiphosura.

Scorpions belong to live-bearing animals, making direct development without metamorphosis.

The female carries young and shows great care for her offspring. Eggs are meroblastic, telolecital and do partial crushing. The cells, coming to the surface, form a single-layer germ circle, which grows and gives the ectoderm, and from the fallen down (in question. Yolk) cells form a lower layer – a common germ for the endoderm and mesoderm.

Then a ring fold is formed on the surface of the embryonic circle, which, growing from the periphery to the center and growing with its inner edges above the embryonic strip, forms embryonic membranes, and its outer leaf forms the so-called serous membrane ( serosa), and the inner – amnion.

The embryonic strip, covered by the amnion, grows in length and is divided into segments marked by transverse grooves not only on the ectoderm but also in the mesoderm, with the latter splitting into paired divisions. The segments of the mesoderm are then split, when they occur inside their cavity, into the skin-muscle and intestinal-muscular plate.

Soon the rudiments of the extremities appear on the segments of the body: on the first segment, on the sides and behind the mouth, the rudiments of tentacles are laid (corresponding in this way to the tentacles, not the tentacles of insects), on the second – jaw tentacles, and on the next four thoracic segments – 4 pairs walking legs.

On 6 front segments of a stomach small rudiments of extremities from which the first pair turns to genital covers, the second – in crested appendages also are formed, and other four pairs disappear, and in their place (vpyachivaniye inside) appear later respiratory tract of pulmonary bags. Nerve nodes of the first segment, innervating tentacles, merge later with the main (supraglottic) nerve node; Thus, although in adult S. the tentacles are cramped and receive nerves from the supraglottic ganglion, they are not homologous to the tentacles of the primary trachea, centipedes, and insects, but correspond to the jaws of Arthropoda.

Scorpions are found exclusively in the hot zone and in the warmer regions of the temperate zone – in the south (Spain, Italy) of Europe, and in our country – in the Crimea, the Caucasus and Turkestan.

During the day they hide under rocks, in rock crevices, etc. and only at night go out for prey.

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