The organs of the lancelet are destroyed. Chordata type. laboratory workshop on zoology of ridges. Reproduction and development of lancelets

On a prepared total preparation of lancelet, we can see the interfreezing of the main organs of the creature (Fig. 6).

Along the entire body of the lancelet (approximately along the midline), a notochord (axial skeleton) stretches from the head to the tail. The preparation clearly shows transverse darkness. The notochord, along with the nerve tube, is sharpened with a semi-tissue membrane. The anterior end of the notochord is visible far beyond the anterior edge of the neural tube, which is the specific boundary of the skullless.

The central nervous system is laid out above the notochord and is represented by the already known nerve tube. By placing the preparation under a slightly stronger microscope, you can see numerous dark spots – Hessian veins (Fig. 6) that grow at the walls of the neural tube close to its inner surface.

At the anterior end of the neural tube, the cephalic dilatation of the neural tube can be noted, which is sometimes called the scutum of the cerebellum, although the anterior part of the nerve tube of the lancelet, which resembles the cerebrum of the spinal cord, is not differentiated.

There is a grass pipe under the chord. It begins with a pre-oral lip, sharpened by numerous tentacles. The mouth emptiness is reinforced with a ring-like fold near the gourd - vitrilo. The walls of the pharynx are pierced by numerous (up to 100) obliquely shaped zebra fissures (Fig. 6). The pharynx gradually transforms into an undifferentiated intestinal tube, which ends in the posterior part of the body with the anal opening. From this tube, just behind the pharynx, comes forward a liver worm, the main part of which is removed from the right side of the gourd.

Figure 7 – Cross-section of a lancelet in the area of ​​the gourd

1 – epidermis; 2 – back swimmer; 3 – metapleural folds;

4 – tulub musculature; 5 - cherry pulp; 6 - chord,

7 – nerve tube; 8 – neurocoel; 9 – cleft of the neural tube;

10 - semi-fabric shell; 11 – myosepti;

12 - interbranchial septa; 13 – endostyle; 14 - suprajaberna borosa; 15 – coelomic channels; 16 – atrial empty;

17 – liver virist; 18 – state vines; 19 – root of the aorta.

In mature individuals, lanceolates have markings (there are 25 pairs of them), which look like dark rounded spots, visible through the vernal wall of the body.

On a preparation of a transverse section of a lancelet in the larynx, one can see under a small microscope the mutual arrangement of organs and details of the creature (Fig. 7).

On the dorsal side, the low dorsal swimmer is clearly visible. On the sides of the body there are extended growths under the pharynx, metapleural folds.

Approximately at the center of the preparation, a chord is expanded, which has an oval shape when viewed. A nerve tube containing a well-known neurocele lies above the notochord. The notochord and nerve tube are swollen with a tissue membrane, from which the myosepta emerge (a splint is visible in their transverse section).

The lower part of the preparation is a section of the pharyngeal (glandular) part of the herbal tube and the outer part of the atria. In the view of the verstat, the pharynx is pierced by a great number of gold-red slits. The endostyle is visible at the bottom of the pharyngeal vial. On the dorsal side of the pharynx, the epibranchial furrow is grown. On the sides of the epibranchial groove there are clearly visible views of two blood vessels - the root of the aorta. The liver worm is visible only in those sections, which grow closer to the rear end of the gourd. In mature individuals, there are expanded grooves on the inner walls of the metapleural folds.

On a preparation of a transverse section of a lancelet in the intestinal area (Fig. 8) we can see the peculiarities of the notochord, the neural tube, the membrane of the tissue, the intestine, the whole and the equal interaction of these organs with what was visible on the previous preparation.

Figure 8 – Transverse section of a lancelet in the intestinal part

1 – epidermis; 2 – back swimmer; 3 – metapleural folds;

4 – muscles; 5 – chord; b – nerve tube; 7 – neurocoel;

8 – semi-fabric shell; 9 – intestines; 10 – dorsal aorta.

The growth of the circulatory system of the lancelet can be seen in the following table and the baby (Fig. 9), fragments of the circulatory system are not visible on the preparations.

As stated, the lancelet has no heart and is replaced by an unpaired celiac aorta. Its walls are formed transversely by dark muscles, which ensure pulsation of the aorta. The blood flows from the cerebral aorta into the cerebral artery, as it grows in the interfabric septa. The venous blood passing through the venous arteries is oxidized directly through the thin walls of these vessels, which are whitened on the surface of the venous fissures. Blood rich in sourness is collected in the root of the aorta. Part of the blood from them goes forward along the small carotid arteries, and the main mass goes straight to the tail. Approximately in the middle of the body, the root aorta merges into the main main canal - the dorsal aorta, which carries blood throughout the body.

Figure 9 – Scheme of the circulatory system of the lancelet

1 – vernal aorta; 2 – cold arteries; 3 – root of the aorta;

4 – carotid arteries; 5 – dorsal aorta; 6 – anterior cardinal veins; 7 – posterior cardinal veins; 8 – Cuverean ducts; 9 – venous sinus; 10 - iliac vein; 11 - chamber system of liver growth; 12 – pechenkova vein

Venous blood from the head part of the body flows backward through the anterior cardinal veins, and from the tail part through the posterior cardinal veins forward. The anterior and posterior cardinal veins of the cutaneous side of the body drain into the thin-walled duct of Cuviere. These ducts drain into the venous sinus.

From the organs of the liver, blood is collected from the axillary vein, which in the hepatic vein is divided into capillaries that stabilize the hepatic venous system. The short hepatic vein carries blood to the venous sinus.

Lanceolate slug - that’s what they called this mysterious creature for a long time. Now we will definitely know all the processes of life of the most primitive representative of the external appearance, internal life of the lancelet and the features of its physiological processes and will be reviewed in our statistics.

History of the discovery and place of discovery

Already in the 18th century, the famous Russian mandrika and Petro Simon Pallas revealed a small essence in the waters of the Black Sea. That sound guessed the mollusk. Further research on the former lancelet showed that this organism is similar to the ancient chordates. Take everything from scratch

In nature, lancelet can be found at the bottom of the seas and oceans. He is alive, buried near the sand, at a depth of up to 25 meters. The larvae of this creature are found in the storage of plankton - a collection of growths and creatures that are on the surface of the water. Because the sand is very fluffy, the lancelets burrow deeper into the sand, exposing only a small part of the anterior end of the body. As the top of the bottom folds over the mule, the smell just lies on its surface. Lancelets can sometimes get stuck between particles of wet sand.

These creatures are willing to settle in colonies, with thousands of individuals living together. Current seasonal migrations add up to several kilometers at a time.

Zovnishna Budova lancelet

Budova's lancelet, and more precisely the shape of the body, gave its name. It looks like a surgical instrument. It's called a lancet. The body of the creature is flattened at the sides. The front end is covered, and the back end is cut obliquely. On the caudal and dorsal sides there are folds that form into a lanceolate-like caudal swimmer in the rear part of the body. The dimensions of this creature are small - up to 8 cm.

Pokrovi

The outer surface of the lancelet is the front of the body. It is represented by a curved fabric - a single-spherical epithelium. The top is covered with a thin ball of cuticle. Like fish, epithelium cells have a lot of mucus that covers their entire body. A ball of successful fabric is woven under the curved fabric.

Skeleton and muscles

The peculiarities of the lancelet are indicated by a system that will provide support for the arm. Vlashtovana won't finish it primitively. The skeleton is represented by a chord that passes through the body from the front end to the back. The muscles look like two cords. The stench extends from both sides to the axial strand. This kind of budova allows the lancelet to grow even without its hands. With the help of additional muscles, he bends the body directly. The chord acts as an antithesis - straightens the lancelet.

Peculiarities of the internal structure of the lancelet

The internal structure is the most primitive among chordates. This type of food is passive. These creatures have filters. The grass system is scraped. It consists of the mouth opening, the pharynx and the tubular intestine with the liver. Jerel's food for the lancelet includes small crustaceans, ciliates, various types of algae, and the larvae of other chordate creatures.

Water filtration is closely related to the process of dehydration. On the walls of the pharynx there are silent cells that swell. This action creates a constant stream of water that passes through the throat and chinks. Gas exchange occurs immediately. After this, water is visible through the winter season. Additional acidity is removed and carbon dioxide is released through the body.

The stench is called nephridia. There are a whole bunch of tubes. The stench completely permeates the body, and at one end it emerges into the peribranchial empty space.

The circulatory system is not closed. The vessel consists of two vessels - the cervical and the dorsal. The heart is daily. Its function is the cerebral vessel, due to which pulsation promotes blood circulation. It will flow with the empty water, washing all the internal organs and thus causing gas exchange.

The nervous system is represented by a tube, which is spread over the chord. Vaughn doesn’t solve the problem, so the lancelet’s brain is a day old. Such a primitive nervous system reflects the weak development of sensitive organs. The stench is represented by the scent, growing on the anterior end of the body. There you can pick up the chemical substances that are near the water in a broken state. Immediately, the tentacles, like the organ of the organ, grow. The nerve tubes are located in light-sensitive cells.

Reproduction and development

The internal structure of the lancelet is determined by the type of statuary system. These are separate creatures from external materials. The development is indirect, the fragments from the eggs develop into larvae, which float in the water and call the fry of the fish. The stinks grub, grow, and after a dozen hours they sink to the bottom, with one end of their body burrowing at the sand. The life of the lancelet becomes trivial on the 3rd or 4th day.

The significance of lancelet in nature and human life

In the lands of Pivdenno-Skhidnaya Asia, lancelets live with hedgehogs. Moreover, in this region there are already hundreds of fisheries. Fishing fishers catch them directly from the deep waters from the sickle to the cross-section several years after release. For which purpose there is a special device. There is a sieve on a bamboo pole. As you stretch out the rock, you can see tens of tons of lancelet. First herbs can be prepared from this, which can be lubricated, boiled or dried for export. The meat of these creatures is lifeless, rich in protein and fat.

Lancelets are primitive marine chordate creatures that belong to the Golovochordov class. They lead a low-impact way of life and eat the way of filtration. Nina stench is an object of industry, and is used for scientific research, the remains of their cultivation and systematic development in the system of the created world allowed the emergence of significant patterns in the process of evolution of chordates.

Lancelet class. The class includes approximately 30 current species.

Lancelets are fragile creatures that spend more than an hour burrowed in the sand. The body looks like a woman, like a fish. On the dorsal side of the long-haired body there is a dorsal swimmer, which passes at the caudal swimmer, which takes the shape of a lancet. The skin of the lancelet is made up of two balls: the outer one - the epidermis and the inner one - the dermis. The epidermis, unlike other chordates, is represented by one ball of cells, which reveals a thin cuticle.

The skeleton of skullless creatures is a notochord - an elastic spring cartilage. The chord serves as a support for internal organs and as a place for attachment of meats. Transversely smooth pulp is composed of several segments.

The nervous system is represented by a nerve tube, which stretches across the body above the notochord. The floor is on the brain and dorsal part of the day. At the cutaneous segment, two pairs of nerves emerge from the neural tube.

At the anterior end of the body there is an olfactory fossa, in which the olfactory cells are localized. The strength of the nerve tube is central to the organs of vision - the eyepieces, which should be exposed to light in the dark through the eyes of the body.

The food particles sink into the tentacles of the roc's mouth to release the mouth virva. The mouth is like a gourd, the walls of which are cut by a great number of silver slits. The food parts are coated with mucus and a short straight tube is placed near the intestines. The cob has a branch and a hepatic virist.

The respiratory system is closely related to the herbal system. The winter crevices, permeated with capillaries, are constantly washed with water. The fissures open in the atria, with one exit opening on the lower surface of the body. The water that flows into the mouth opening and further into the gourd is filtered through the winter fissures into the atrial emptiness, and is discharged through the outlet opening.

The circulatory system is closed. The heart is silent, and its role is played by pulsating blood vessels. These vessels supply blood to the glands, and then to all organs of the body. The blood does not contain dilute pigments.

The vision system of the lancelet is similar to the metanephridia of spinal worms. At one end the tubes are opened as a whole, and at the other end they are empty, and signs of waste products are removed from the body.

Lancelets are separate. State plants do not show any visible ducts, gametes are seen in the atrial void, and come out into the water. Covered externally. As a result of the crushing of the fertilized egg, a larva hatches. She's already crumbling, actively wanting to serve for the settlement. The presence of the larval stage is characterized by the peculiarity of the development of the lancelet.

Subtype Bezkrania (Acrania) or Cephalochordata (Cephalochordata)

Skullless - marine, especially bottom-dwelling creatures, which always preserve the signs of the type of chordates. The head is not supported, the skull is of the same size (from the name). The entire body, including the internal organs, is segmented. These are the most primitive chordates, so their evolution is important for understanding the progression of chordates and cob stages of their evolution.

Representatives class Lancelets they hang around in shallow waters, near the coastal parts of warm seas and oceans. In our countrylancelets They meet in the valleys of the Black Sea and the Sea of ​​Japan. About 30 current species are visible.

Head of the lancelet sign

Lancelets are small,call to guess the fry fish,sea ​​creatures. In her future lifeto show signs, characterneither for worms nor molluscs.

Ale at the same hour they haveorgan that produces lanceletsmore than hrobaks and mollusks. Tsey organ - chord - is itselfI’ll spring all over, as in the long courseOur evolution will be further developed inKistkovy ridge.

Well, we can say: in the backgroundthe types we looked at without permissionThe lancelet reveals nocturnal creatureswith the first essence, the life of the body untilwhich is pulled by the supporting axial skeleton.І whose simple pristosuvannya,allows the creature more of itsfeel free to use your body, it was suedit was possible to create chordov volodarsseas, land and winds.

Zovnishna Budova lancelet

Lancelet hesitates on smalldepths of warm seas near the great balland a fluffy squeak. Dovzhina of the unitedfrom the sides of the erysipelas body of the lanceletset 4-8 cm. The body is placed on the pemiddle and back ends. Tailframed with a hide fold -tail swimmer, guessbehind the shape of a surgical instrumentment - lancet. Below the body there isskin fold that closeszyabrovo empty (she steals toadsri vid smіchenya).

More than an hour lanceletcarry out, buried in the sand and riseshaving twisted the named anterior end of the body, onwho knows the mouth, oozing10-20 pairs of tentacles. Lanceletsrarely deprive your food during the daynow and ask to move a little. Stinksbe afraid of bright light and activity in night time.

I want to fold the lancelet,head rank, single-roommature, as well as other roots,Ciliates, radiolaria, eggs andrepairs of the spineless. Lanceletattracts microscopic organswe are important near the water, through the mouthopen Strum water from oral mugyou carry parts of the hedgehog to the fork, aboutlowered with winter-green openings.Here the water is thrown out completely.

Inner lancelet

Cover the body of the lancelet with thinskin, through which one can shine throughm'yazi. Rotated from the sidesbody two lines of meat separation of buttriver partitions for 50-80 hoursstkiv. The lancelet can help themtry to finish twoNya. The body flexes first in one direction, then inThe other one floats and the dawn Go to the ground.

The basis of the body of the lancelet is the spring strizhen - the chord. The nerve tube is rotted above the chord. Below the chord there is a grass system.

Grass system. The middle part of the lancelet's mouth is covered with clinae with viyas. The stench creates a steady stream of water, which simultaneously passes microorganisms through the mouth. The pharynx is pierced by numerous (over 100) zebra slits. Through this opening, water floods the etching system. The hedgehog goes straight into the intestine, where it is likely to be poisoned. Excess hedgehogs are removed through the anal opening.

Dihal system. The walls of the gills are pierced by a network of different blood vessels. They experience gas exchange between water and blood. The cream of the hare, the breath of the lancelet comes through the skin.

Circulatory system. The circulatory system of the lancelet is closed. Along the dorsal vein from the gills to the internal organs the flow is saturated with acidity arterial shelter. From the internal organs there is blood along the ventral vessel to the gills venous , infused with carbon dioxide. Thus, the lancelet has one colo of blood loss. The flow of blood will ensure the shortening of several blood vessels.

Nervous system. Under the skin and muscles above the chord, the nerve tube is grown. Right in the nerve tube there are a number of groups of light-sensitive cells, with the help of which the lancelet produces light from the dark. The lancelet has scent holes. There are scattered edges of woven welts on the skin. The lancelet has a low-impact way of living, which explains the weak development of the organs of the senses. The brain was not visible.

Visible system. The organs of the lancelet are a number of dozens of visible tubes, one end of which opens into the empty body, and the other flows into the renal canal. A number of underground channels are visible on the top.

State system. Lancelets are separate creatures. Plants also “segmentally” collect ovaries (in females) and seed plants (in males).

Reproduction

Lancelets reproduce in the spring, in the spring and in the spring, on the Black Sea - from the end of the grass to the ear of the sickle. Immediately after the sun sets, females begin to sprout mature eggs with a diameter of 0.1 mm. Males see sperm in the water. The development of frozen eggs and larvae is recovered in the waste water. The larvae, 3.6-5.2 mm long, rise to the surface at night and sink to the bottom of the water during the day. Until the end of the first rock of life, the lancelet reaches up to 30 mm, another rock - 40 mm, the third - 60 mm and the fourth - 70 mm. Live lancelets 1-4 rocks.

PIDTYPE OF CRANIAL ACRANIA

TOPIC 1. BUDOV'S LANCELLANTA

SYSTEMATICALLY POSITIONING THE OBJECT

Type Chordovia, Chordata
Subtype Skullless, Acrania
Clas Golovochordov, Cephalochordata
Representative - Lancelet, Branchiostoma lanceolatutn Pall.

MATERIAL AND DESIGN

For one or two students you need:
1. A preparation of a whole lancelet, lying on the side of a glass slide, cleared and garnished with carmine.
2. Preparation of a transverse section of a lancelet in the pharyngeal area.
3. Preparation of a transverse section of a lancelet in the intestinal part.
4. Tripod magnifying glass.
5. Microscope.

ZAVDANNYA

Look at the external appearance of the fixed lancelet, and then, under a magnifying glass and microscope, see the systems of its organs. Every student needs to create the following little things in his album:
1. Whole lancelet (side view) with organ systems (magnifying glass).
2. Transverse section of the lancelet in the throat (microscope).
3. Transverse section of a lancelet in the intestinal tract (microscope).

Dodatkove Zavodnya

Take a close look at the biological preparations:
1. Solitary ascidium.
2. Colonial ascidian.
3. Ascidian larva (microscope).
To predict the systematic formation of ascidians:

Type Chordovia, Chordata
Subtype Obolontsi, Tunicata
Class Ascidiae, Ascidiae

Pay attention to the similarities and differences between the lancelet and tunicates.

VISTERING VIGLEAD AND INTERNAL ORGANS OF THE LANCELETA

The external appearance of the lancelet and the hidden plan of its bud will be examined under a magnifying glass (magnification 8x) on a total preparation. The reported details will be viewed in cross-sections under the minimum power of the microscope.

Small 2. The glamorous look and growth of the internal organs of the lancelet:
1 - pre-oral leukina, 2 - tentacles, 3 - dorsal swimmer, 4 - caudal swimmer, 5 - infra-tail swimmer, 6 - atriopore, 7 - metapleural fold, 5 - anal opening, 9 - myomer, 10-myosepta, 11 12 - nerves tube, 13 - Hessian vein, 14 - unpaired “vechka”, 15 - oral opening, 16 - vitrilo, 17 - cowl, 18 - zebra slit, 19 - interbranchial septum, 20 - intestine, 21 - 2 pechenkovy - articular glands

External look. At the anterior end of the subcutaneous body of the lancelet, the peroral band grows (Fig. 2, 1), sharpened with tentacles (Fig. 2, 2). In the middle, the entire body is sharpened by an unpaired fin fold: along the dorsal side of the body there is a low dorsal fin (Fig. 2, 3; Fig. 3, 1; Fig. 4, 1); the posterior end of the body is lined with a larger tail swimmer (Fig. 2, 4), which resembles the shape of a medicinal lancet (the shape and name of the creature). The caudal swimmer on the ventral side passes into the infra-caudal swimmer (Fig. 2, 5), which ends approximately at the equal rear third of the lancelet’s body. This place has a special opening - atriopore (Fig. 2, 6), which indicates atrial emptyness (division below) from the external media. From the atriopore to the perioral verma, paired metapleural folds run between the cervical and lateral surfaces of the body (Fig. 2, 7; Fig. 3, 2). Behind the atriopore, near the posterior end of the body of the lancelet, there is an anal opening (Fig. 2, 8).

Skinny cover. The body of the lancelet is covered with a single-spherical epidermis (Fig. 3, 3; Fig. 4, 3), which is underlain by a draglistous semi-tissue ball of skin - corium, or cutis (Fig. 3, 4; Fig. 4, 4).

Small 3. Transverse section of a lancelet in the pharyngeal area:
1 - back swimmer; 2 - metapleural folds; 3 - epidermis; , 12 - Zyabrova Shilina, 13 - Migzhaberna Partition, 14 - Endostil, 15 - Najaberna Borozhny, 16 - Pechinki Virist, 17 - Statva Zaporoza, 18 - atrial Gorozhnina, 19 - Zilisna Gorozhnina, 20 - transverse M'yaziyazi

M'yazova system. The musculature of the lancelet has a metameric (segmental) structure. The cutaneous segment (myomere or myotome) is curved and the apex straightens forward (Fig. 2, 9). The vascular myomeres are reinforced with one type of draggy composite tissue partitions - myosepta (Fig. 2, 10). Through the curvature of the myomeres in transverse sections one can see a splint of myomeres (Fig. 3, 10; Fig. 4, 10) and myoseptum (Fig. 3, 9; Fig. 4, 9). The dimensions of one side are displaced by half a segment in relation to the dimensions of the other side (muscle asymmetry). A special ball of transverse flesh passes along the ventral side of the body in front of the atriopore (Fig. 3, 20).

Small 4. Transverse section of the lancelet in the intestinal part:
1 - dorsal swimmer, 2 - subcaudal swimmer, 3 - epidermis, 4 - cutis, 5 - notochord, 6 - nerve tube, 6a - neurocoel, 7 - Hessian vein, 8 - draglista membrane of the notochord, 9 - myosepta, 10 - myomere, 11 - intestinal wall, 12 - empty intestine, 13 - empty intestine

Skeleton. The axial skeleton of the lancelet is represented by a dorsal string or chord (chorda dorsalis - Fig. 2, 11; Fig. 3, 5; Fig. 4, 5), which passes through the middle of the body and sounds in front and behind. The notochord projects forward beyond the anterior end of the neural tube (hence the name of the class - cephalochordates). Large vacuolated cells that form the notochord give it a characteristic transverse darkness (visible when viewed from the side). The notochord is sharpened by a membrane made of precious synthetic tissue (Fig. 3, 5; Fig. 4, 5); The young parts of these membranes, which look like the myoseptum, are divided into fleshy segments, thereby ensuring the connections between the muscles and the notochord. The springiness of the chord is ensured by the movement of the muscles and the springiness of the membrane.

The unpaired fin fold is supported by stacked, draggy, succulent tissue growths; They can be seen in many of the prepared preparations.

Nervous system. The central nervous system is represented by a thin nerve tube (Fig. 2.12; Fig. 3, 6; Fig. 4, 6), which lies above the notochord. On the total preparation there is clearly visible a lance of black dots, which are light-sensitive organs - the Hessian eye (Fig. 2, 13), which are formed from pigment cells, which is evident. The eyes of Hesse are located directly at the point of the neural tube (Fig. 3, 7; 4, 7) and are clearly visible throughout the prosthesis. At the anterior end of the nerve tube, which creates small expansions (“cerebral fur”), there is a large pigmented area - the “gypsy eye” (Fig. 2, 14); Its function is not explained. The unpaired eye is clearly marked by the appearance of a dark spot (it’s easier to see on a total preparation under a low-magnification microscope).

In a transverse transection, the nerve tube has a slightly tricutaneous shape (Fig. 3, 6; Fig. 4, 6). At the center, a very small internal empty space of the nerve tube is visible - the neurocoel (Fig. 4, 6a). Hesse's eyes concentrate on the neurocele. As in all chordate creatures, the lancelet's nerve tube is protected by a path of the larynx of the primary nerve scarf with further enlargement of its edges. On preparations of transverse sections, the trace of this growth is well marked by the appearance of a vertical line that passes from the neurocoelus to the dorsal surface of the neural tube.

With good preparations, it is possible to study that the roots of the spinal nerves exit the neural tube: the dorsal ones at the anterior part of the skin segment and the vernal ones at the posterior part. In contrast to the larger chordates, the dorsal and ventral roots of the non-cranial ones do not unite into a single nerve.

Organi etching and dikhannya. At the bottom of the perioral funnel there is a small oral opening (Fig. 2, 15), with a fleshy septum - vitrilo (Fig. 2, 16). On its anterior surface there are thin streaks of the migrating organ. The mouth opening leads into a large chamber (Fig. 2, 17; Fig. 3, 11), the walls of which are pierced by numerous (more than a hundred pairs) ginger fissures (Fig. 2, 18; Fig. 3, 12), with reinforcements of one type thin obliquely shaped interbranchial septa (Fig. 2, 19; Fig. 3, 13). Therefore, not only when viewed from the side, but also in transverse sections, the side walls of the pharynx appear as perforated by numerous fissures (Fig. 3, 12).

Zyabrovi slits lead to the superfluous pharynx atria, or to the superpharyngeal pharynx, empty (Fig. 3, 18). The atriopore opens up from the sides and bottom and opens up called the opening - atriopore (Fig. 2, 6). In a seemingly blind, closed virostus, the atrial empty space extends backwards a little beyond the atriopore. The water that enters the gourd through the mouth opening, passes through the clefts into the atria and is excreted through the atriopor.

The bottom of the pharynx passes through the subbranchial sulcus or endostyle (Fig. 3, 14). In transverse section, the endostyle has the shape of a rhinvi. Along the dorsal side of the pharynx there is a supragial sulcus (Fig. 3, 15). The sore furrows are lined mostly with epithelium, in the middle of the cells, which contain cells that show mucus. It appears that the mucous membranes of the endostyle are slimy cells that are chasing to the front end of the pharynx, in front of the stream of water, enveloping and spluttering grub parts that have been sunk into the gourd with the stream of water. Then, along two supracillary grooves, the breasts are glued together with mucus and are inserted into the epibranchial groove, in which case they are usually brought back to the cob of the intestine.

Sounding sharply, the lining passes through a very short intestine, which does not contain any vagina (Fig. 2, 20; Fig. 4, 11, 12), which ends in the anal opening (Fig. 2, 8). From the anterior end of the intestine, just behind the pharynx, a blind, finger-like hepatic virist extends straight forward (Fig. 2, 21), which is right-handed in front of the pharynx (Fig. 3, 16).

State system. Lancelets are separate creatures, and apart from state dimorphism, they don’t stink. There are about 25 pairs of rounded ridges (Fig. 2, 22) lying at the walls of the body in the area of ​​the back half of the pharynx and the cobalt part of the intestine. When viewed under a microscope in cross-section, the ovaries (Fig. 3, 17) are easily dissected from the ovules due to the presence of large eggs. There are no sublingual ducts in the lancelet. Mature products fall out through a tear in the wall of the duct into the atrioventrium and flow with a stream of water through the atrioporus. Congestion occurs in the outer middle.

Empty body. Like all chordates, the lancelet bears the second empty part of the body – the halo (Fig. 3, 19; Fig. 4, 13). However, as a result of the strong development of atrial emptiness in general in the pharynx area, it is greatly reduced and is saved only on the sides of the upper part of this area and under the endostyle. At the back of the body there is a sign of apology for good; It occupies the entire space between the body wall and the intestine (Fig. 4, 13).

Circulatory system. It is not visible on the initial preparations, so you have to look at the diagrams to see what is available (Fig. 5). The circulatory system is closed, the heart is silent; there is only one bleeding. On the varicose side of the pharynx there is a cerebral aorta, from which the cerebral arteries extend to the cutaneous interbranchial septum and carry venous blood. The blood flow is created by the pulsation of the cerebral aorta and the dilated veins of the cerebral arteries. Oxidized in the interbranchial septa, the arterial blood flows through the vinous arteries into the paired root aorta, which passes above the pharynx, and from behind the gourd flows into the azygos dorsal aorta; After this, blood is delivered to all areas of the body.

Small 5. Scheme of the circulatory system of the lancelet (bottom view):
1 - Vinosy Zyabrovsky Artheri, 2 - Korinnya of the Aorti, 3 - spin aorta, 4 - rear cardinal avenes, 5 - front -line carp, 6 - kyuv'yrovi ducts, 7 - tail of Vienna, 8 - Vienna Pidkishkova, 9 - Komirna system hepatic vein, 10 - hepatic vein, 11 - celiac aorta with cerebral arteries, what to come from it bring

Venous blood from the anterior part of the body is collected in the paired anterior cardinal veins, and from the posterior part - in the posterior cardinal veins. The anterior and posterior cardinal veins of the cutaneous side flow into the ducts of Cuviere, which drain into the cerebral aorta. Carrying venous blood from the intestine, the axillary vein in the hepatic vein breaks up into capillaries (continues the coronary system), which then flow, condensing the hepatic vein; It flows into the vernal aorta.

The visual system of the lancelet is of nephridial type. With this everyday life it is necessary to get acquainted with the assistant, the fragments on the basic nephridium preparations are not visible.

VISNOVOK

The lancelet (and other species of the skullless subtype, Acrania) has all the typical characteristics of the chordate type: the notochord, the central nervous system, like the tubes and pharynx, are penetrated by silver fissures.

Primitiveness, obvious simplicity of organization of the skullless muscles are revealed in the present: weak development of skeletal structures (the supporting function of the notochord and often dragging tissue), the lack of differentiation of the central nervous system into the head and spinal cord, weak development of sensory organs (represented by tissues, bodies, and glasses Hessian in the same nerve tubes), metamerism of the growth of the herbaceous buds, metamerism of the growth of the type of visible organs of the herbal tube (nephridia), which is what the organs of seeing of the worms guess, clearly the differentiation of the herbal tube is still weakly expressed, one sphericity of the skin epithelium, the presence of dry substances in the skin and etc. These features of the organization are related to the main reasons for the biology of the lancelet: its very low friability and passive feeding, if the creature does not actively resound and does not scoop up the species, but is satisfied with the hedgehog, as in pours into a gourd with continuous filtration of water.

It should be noted that the emergence of the skullless subtype is a very important stage of evolution. Here, a “distant” plan was clearly formed, which would allow the further differentiation of organ systems to sharply raise the level of the organization. This very way is the evolutionary development of the most progressive gills of chordate creatures - a subtype of spinal creatures.

From an evolutionary point of view, the most important thing was the formation of the myochordal complex: a clearly differentiated internal supporting skeleton in the form of the notochord and the increased mass of the segmented meat system associated with it. In larval chordates, which are spineless, and in the lower chordates, the flesh has no support in the middle of the body and is connected to the skin, forming a skin-muscle sac. Evolutionarily important was the emergence of a closed circulatory system with this type of expansion of the main blood vessels (vessels), which appeared to be suitable for spine animals that lead a watery way of life, regardless of the sharp increase in the level of metabolic rate of speech. . These peculiarities of the organization allowed one of the ancient skullless legs to move to a more similar type of ruk and date to the spinal cob.

Today's skullless ones (including lancelets) are the sites of ancient skullless ones. Regardless of their primitiveness, they have been preserved to this day due to the specialization that allowed them to occupy and successfully fill their living niche - scouring the plots of the seabed. The morphological features that ensure this specialization are quite varied.

As you can see, the body is dirty and marked on the ground. Among the primary epithelial cells are the cells that produce mucus; It protects the delicate skin from damage when buried in soil. The burrow is facilitated by a large mass of fleshy segments, a lancet-like shape of the tail, and prominent anterior ends so that the chord reaches almost to the very anterior end of the body, clearly visible in front of the end of the neural tube. The free-swimming lancelet larva has an atrial void every day. It develops during the period of metamorphosis during the transition to the bottom way of life and protects the green crevices from being mixed with particles in the soil. A sharp increase in the number of winter crevices and an increase in the size and thickness of the pharynx absorbs an increased flow of water and thereby ensures the survival and feeding of the creature that has sunk into the ground. Differentiation of the pharynx (created in it by the endostyle and the epibranchial groove) and the accumulation of particles of liquid mucus, which is visible as endostyle cells and collapses in front of the stream of water, contributes to greater strength of the liquid, which o is filtered, and the strengthening of the secretory part of the intestine (liver virostiv) is reduced. However, the low fluidity of the blood flow (heart activity) and the nephridial vision system mean a remarkably low rate of speech exchange.

additional literature

Gurtova N. N., Matveev B. S., Dzerzhinsky F. Ya. Practical zootomy of spinal animals. Lower chords, gapless fish. M., 1976.
Kovalevsky O. History of the development of Amphioxis lanceolatus - Notes of St. Petersburg. Academy of Sciences. Ser. 7, vol. 11 no. 4, 1867.
Shmalhausen I. I. Fundamentals of the vertebral anatomy of spinal creatures. M., 1947.