Everyone knows about mammals from the school curriculum. Did you know that an egg-laying mammal is a separate animal species that lives only on the territory of one continent - Australia? Let's take a look at this special kind animals in more detail.

Discovery of oviparous

For a long time, the existence of animals unique in their kind that breed by incubating eggs was not known. The first message about these creatures came to Europe in the 17th century. At this time, the skin of a marvelous creature with a beak, covered with wool, was brought from Australia. It was a platypus. The alcoholized copy was brought only 100 years later. The fact is that platypuses practically do not tolerate captivity. It is very difficult for them to create conditions during transportation. Therefore, observations of them were carried out only in the natural environment.

Following the discovery of the platypus, news came of another creature with a beak, only now it is covered with needles. This is an echidna. For a long time, scientists argued about which class to classify these two creatures. And they came to the conclusion that the platypus and echidna should be placed in a separate detachment. This is how the detachment One-pass, or cloacal, appeared.

Amazing platypus

A unique creature of its kind, leading a nocturnal lifestyle. The platypus is distributed only in Australia and Tasmania. The animal lives half in the water, that is, it builds holes with access to the water and to land, and also feeds in the water. A creature of small size - up to 40 centimeters. It has, as already mentioned, a duck nose, but at the same time it is soft and covered with skin. Only in appearance it is very similar to a duck. There is also a 15 cm tail, similar to a beaver's tail. The paws are webbed, but at the same time they do not prevent the platypus from walking on the ground and digging holes perfectly.

Since the genitourinary system and intestines exit the animal into one hole, or cloaca, it was assigned to a separate species - cloacae. It is interesting that the platypus, unlike ordinary mammals, swims with the help of its front paws, and the hind legs serve as a rudder. Among other things, let's pay attention to how it reproduces.

Platypus breeding

Interesting fact: before breeding, animals fall into a 10-day hibernation, and only after that does it begin mating season. It lasts almost the entire autumn, from August to November. Platypuses mate in the water, and after a two-week period, the female lays an average of 2 eggs. Males do not participate in the later life of offspring.

The female builds a special hole (up to 15 meters long) with a nest at the end of the tunnel. Lines it with raw leaves and stems to maintain a certain humidity so that the eggs do not dry out. Interestingly, for protection, she also builds a barrier wall 15 centimeters thick.

Only after preparatory work she lays her eggs in the nest. The platypus incubates eggs by curling up around them. After 10 days, babies are born, naked and blind, like all mammals. The female feeds the babies with milk, which flows from the pores directly through the fur into the grooves and accumulates in them. Babies lick milk and thus feed. Feeding lasts about 4 months, and then the kids learn to get food on their own. It was the method of reproduction that gave this species the name "egg-laying mammal".

extraordinary echidna

Echidna is also an egg-laying mammal. This land creature large sizes reaching up to 40 centimeters. It also lives in Australia, Tasmania and the islands of New Guinea. In appearance, this animal looks like a hedgehog, but with a long narrow beak, not exceeding 7.5 centimeters. Interestingly, the echidna has no teeth, and it catches prey with the help of a long sticky tongue.

The body of the echidna is covered on the back and sides with spines, which were formed from coarse wool. Wool covers the belly, head and paws is fully adapted for a certain type of food. It feeds on termites, ants and small insects. She leads a daytime lifestyle, although it is not easy to find her. The fact is that she has a low body temperature, up to 32 degrees, and this does not allow her to endure a decrease or increase in ambient temperature. In this case, the echidna becomes lethargic and rests under trees or hibernates.

Echidna breeding method

Echidna is an egg-laying mammal, but it was only possible to prove this in early XXI century. interesting mating games echidna. There are up to 10 males per female. When she decides she's ready to mate, she lays down on her back. At the same time, males dig a trench around it and begin to fight for supremacy. The one who turned out to be stronger copulates with the female.

Pregnancy lasts up to 28 days and ends with the appearance of one egg, which the female moves to the brood fold. It is still not clear how the female moves the egg into the bag, but after 10 days the baby appears. The cub comes into the world incompletely formed.

Young

The birth of such a baby is very similar to the birth of young marsupials. They also pass their final development in the mother's pouch and leave her as adults, ready for independent life. Interesting fact: marsupials also common only in Australia.

How does the baby echidna appear? He is blind and naked, his hind limbs are not developed, his eyes are covered with a leathery film, and fingers are formed only on the front paws. It takes a baby 4 hours to get to milk. Interestingly, in the mother's pouch there are 100-150 pores that secrete milk through special hairs. The kid just needs to get to them.

The baby is in the mother's pouch for about 2 months. He gains weight very quickly due to nutritious milk. Echidna's milk is the only one that has pink color at the expense a large number it has iron. Feeding continues up to 6.5 months. After the young growth learns to get food on its own.

prochidna

Prochidna is another egg-laying mammal. This creature is much larger than its counterparts. The habitat is the north of New Guinea and the islands of Indonesia. The size of the prochidna is impressive, up to 80 centimeters, while its weight is up to 10 kilograms. It looks like a echidna, but the beak is much longer and the needles are much shorter. She lives in mountainous areas and feeds mostly on worms. The structure of the oral cavity of the prochidna is interesting: her tongue has teeth, and with the help of it she is able not only to chew food, but, as has been noted, even to turn over stones.

This species is the least studied, as it lives in the mountains. But at the same time, it was noticed that the animal does not lose mobility in any weather, does not hibernate and is able to regulate the temperature. own body. reproduction oviparous mammals, to which the prochidna belongs, occurs in the same way as in the other two species. She hatches only one egg, which is placed in a bag on her stomach, and feeds the cub with milk.

Comparative characteristics

Now let's look at the types of mammals that live on the Australian continent. So, what is the difference between oviparous, marsupial and placental mammals? To begin with, it must be said that all mammals feed their offspring with milk. But the birth of babies has huge differences.

Oviparous animals have one thing in common. They lay eggs like birds and incubate them for a certain amount of time. After the birth of the offspring, the mother's body produces milk, which the babies eat. It should be noted that the cubs do not suck milk, but lick it from the grooves on the female's stomach. The absence of nipples distinguishes oviparous from other mammals.

They have a pouch, hence their name. The pouch is located on the abdomen of females. A newborn baby, having reached it, finds a nipple and, as it were, hangs on it. The fact is that babies are born unformed and spend several more months in their mother's pouch until they are fully developed. It must be said that oviparous and marsupial mammals are similar in this respect. Echidna and prochidna babies are also born underdeveloped and placed in a kind of brood fold.

What about placental mammals? Their babies are born fully formed due to the presence of a placenta in the uterus. Due to it, the process of nutrition and development of the cub takes place. The majority of animals are placental.

Such a variety of species exists on one continent.

Oviparous - belong to the class of mammals, a subclass of cloacae. Among all known vertebrates, monotremes are the most primitive. The squad got its name due to the presence of a special characteristic among the representatives. Oviparous have not yet adapted to live birth and lay eggs to reproduce offspring, and after the babies are born, they feed them with milk.

Biologists believe that monotremes came from reptiles, as an offshoot of a group of mammals, even before the birth of marsupials and placental animals.

Platypus - a representative of egg-laying

The structure of the skeleton of the limbs, the head section, the organs of the circulatory system, the breathing of the first animals and reptiles is similar. in the fossils mesozoic era the remains of oviparous were found. Monotremes then inhabited the territory of Australia, and later occupied the South American expanses and Antarctica.

To date, the first animals can only be found in Australia and the islands located nearby.

Origin and diversity of mammals. Oviparous and real animals.

The ancestors of mammals are reptiles of the Paleozoic. This fact confirms the similarity in the structure of reptiles and mammals, especially at the stages of embryogenesis.

In the Permian period, a group of theriodonts, the ancestors of modern mammals, was formed. Their teeth were placed in the recesses of the jaw. Most animals possessed a bony palate.

However, the environmental conditions that formed during the Mesozoic era contributed to the development of reptiles and they became the dominant group of animals. But the climate of the Mesozoic soon changed dramatically and the reptiles failed to adapt to the new conditions, and mammals occupied the main niche of the animal world.

The mammal class is divided into 2 subclasses:

• Subclass First Beasts or Single Pass;
• subclass Real animals.

Real animals and monotremes are united by a number of signs: hairy or needle outer cover, mammary glands, hard palate. Also, the first animals have common characteristics with reptiles and birds: the presence of a cloaca, laying eggs, and a similar skeletal structure.

Detachment Single pass - general characteristics

Echidna is a representative of monotremes

Oviparous - animals of small size with a flattened body from top to bottom, short limbs with large claws and a leathery beak. They have small eyes and a short tail. In oviparous, the external auricle is not developed.

Only representatives of the platypus family have teeth and they look like flat plates equipped with protrusions along the edge. The stomach is only for storing food; the intestines are responsible for digesting food. Salivary glands very developed, large, the stomach passes into the caecum, which, together with the urogenital sinus, flows into the cloaca.

The first animals do not have a real uterus and placenta. Reproduction by laying eggs, there is little yolk in them, and the shell includes keratin. The mammary glands have many ducts that open on the ventral side in special glandular fields, since there are no nipples in monotremes.

Body temperature can vary: it does not rise above 36 ° C, but with a significant cooling it can drop to 25 ° C. Echidnas and platypuses do not make sounds, as they lack vocal cords. The life expectancy of an echidna is about 30 years, platypuses - about 10. They inhabit forests, steppes with shrubs and are even found in highlands(at an altitude of up to 2500m.).

Representatives of oviparous have poisonous glands. On the hind limbs there is a bone spur through which a poisonous secret flows. The poison is potent, in many animals it provokes disruption of vital organs, it is also dangerous for humans - it causes severe pain and extensive swelling at the site of the lesion.

Trapping and hunting for representatives of the detachment is prohibited, as they are listed in the Red Book due to the threat of extinction.

Platypus and Echidna

The platypus and echidna are oviparous, mammals, the only representatives of the order.

A small animal about 30-40 cm long (body), tail up to 15 cm, weighing 2 kg. Males are always larger than females. It lives near water bodies.

Five-fingered limbs are well suited for digging the ground, on the coast, platypuses dig holes for themselves about 10 meters in length, equipping them for later life (one entrance is underwater, the other is a couple of meters above the water level). The head is equipped with a beak, like a duck (hence the name of the animal).

Platypuses are in the water for 10 hours, where they get food: aquatic vegetation, worms, crustaceans and molluscs. Swimming membranes between the toes on the front paws (almost not developed on the hind legs) allow the platypus to swim well and quickly. When the animal dives under water, the eyes and ear openings close, but the platypus can navigate the water through sensitive nerve endings in its beak. He even has electroreception.

Platypuses bear cubs for a month and give offspring from one to three eggs. First, the female incubates them for 10 days, and then feeds them with milk for about 4 months, and at the age of 5 months, the platypuses, already capable of independent life, leave the hole.

Oviparous mammals also include echidna, found in forests appearance looks like a hedgehog. To obtain food, the echidna digs the ground with powerful claws and, with the help of a long and sticky tongue, receives the necessary food (termites, ants).

The body is covered with spines that protect it from predators; when danger approaches, the echidna curls up into a ball and becomes inaccessible to enemies. The female weighs approximately 5kg and lays an egg weighing 2g. Echidna hides the egg in a bag formed by a leathery fold in the abdominal region and wears it, heating it with its warmth, for two weeks. A newborn cub is born with a mass of 0.5 g, continues to live in the mother's pouch, where it is fed with milk.

After 1.5 months, the echidna leaves the pouch, but continues to live in a hole under the protection of its mother. After 7-8 months, the baby is already able to find food on its own and differs from the adult only in size.

Detachment single pass

Rightly considered one-way representatives special detachment and even a subclass of mammals*.

* A separate subclass of egg-laying mammals, or first animals (Prototheria), in the modern fauna is represented only by a detachment of monotremes, known since the Early Cretaceous. Monotremes live only in Australia and on the adjacent islands.

That the monotremes do indeed feed their young with milk has long been established beyond any doubt; but only Gegenbaur's exact investigations have introduced us to the true nature of their mammary glands. Before for a long time they were not noticed, and therefore already at the beginning of this century they were sure of the validity of the indication made by the researcher who first discovered the platypus, namely, that the platypus lays eggs; later this indication was considered a fable. But on September 2, 1884, Haake informed the Royal South Australian Society in Adelaide that a few weeks earlier he had found an egg in a large, hitherto unknown bag of a live female echidna, which he showed at the meeting. On the same day a telegram was read in Montreal informing the members of the British Association assembled there that another explorer then working in Australia, Caldwell, had become convinced that monotremes lay eggs. Gegenbaur proved in 1886 that the glands that deliver food to the young of monotremes that have hatched from eggs do not correspond in structure to the sebaceous glands, as in other mammals, but represent altered sweat glands. If we add to this that the platypus has, during a significant period of its life, although real teeth, but very different from the teeth of all other living mammals, as Thomas discovered only in 1888, and that, in contrast to all other warm-blooded animals, the temperature of the blood monotremes does not exceed 28 degrees Celsius **, it will not seem strange if we separate them as the second main division of the class of mammals from the first, to which we must refer, as true mammals, marsupials and higher mammals, vertebrates.

* * The body temperature of the platypus averages 32.2 degrees Celsius, echidna 31.1 degrees. The representatives of the detachment still have imperfect mechanisms of thermoregulation, and the temperature can fluctuate within 25-36 degrees.

Monotremes are similar to other mammals primarily in their outer coverings: the platypus has fur, and the echidna has needles; otherwise, they differ significantly in appearance from other known forms of this class. A horny beak, resembling the beak of swimming birds, replaces their muzzle; the excretory ducts of the intestines, urinary and genital organs open together into the so-called cloaca. We meet this formation again in birds, which the monotremes resemble, except for eggs with a large yolk, also in the presence of an arch formed from the clavicles fused together, and in that their right ovary is partly underdeveloped. If in this way it is impossible not to notice their relationship with birds, as well as with reptiles and amphibians, then they are connected with marsupials by the presence of marsupial bones in the pelvis.
Single pass - small mammals with a dense, somewhat flattened body from top to bottom, very short legs, beak-shaped jaws, dressed with dry skin, small eyes, short tail, legs spread outward with large claws; in the male, a hollow spur is noticed on the heel, which stands in connection with a special gland. There is no external auricle at all; the teeth, which exist only in the platypus, consist of flat saucer-shaped plates, equipped with tubercles or notches on the edge that are adjacent to the jaws. On the skull, many sutures fuse very early; the costal cartilages also completely ossify. The salivary glands are large, the stomach is simple, the caecum is very short. There is no true uterus, as the oviducts open into the cloaca*.

* The stomach of one passerine is devoid of digestive glands and serves only to store food, like the goiter of birds. The structure of the limbs is very similar to that of a reptile; when walking, the legs are not under the body, as in other animals, but are widely spaced apart, like in crocodiles or lizards.

In addition to the bones of one extinct echidna, fossil teeth have been found that are similar to the teeth of a platypus; at present, this peculiar detachment is limited to two families - echidnas and platypuses.

Life of animals. - M.: State publishing house of geographical literature. A. Brem. 1958

See what "Single-pass detachment" is in other dictionaries:

Monotremes (or oviparous) are the most primitive among modern mammals, retaining a number of archaic structural features inherited from reptiles (oviposition, the presence of a well-developed coracoid bone not connected to ... Biological Encyclopedia

lesson type - combined

Methods: partially exploratory, problem presentation, reproductive, explanatory-illustrative.

Target: mastering the skills to apply biological knowledge in practical activities, to use information about modern achievements in the field of biology; work with biological devices, tools, reference books; conduct observations of biological objects;

Tasks:

Educational: the formation of a cognitive culture, mastered in the process of educational activities, and aesthetic culture as an ability to have an emotional and valuable attitude towards objects of wildlife.

Developing: development of cognitive motives aimed at obtaining new knowledge about wildlife; cognitive qualities of the individual associated with the assimilation of the basics scientific knowledge, mastering the methods of studying nature, the formation of intellectual skills;

Educational: orientation in the system of moral norms and values: recognition of the high value of life in all its manifestations, the health of one's own and other people; ecological consciousness; education of love for nature;

Personal: understanding of responsibility for the quality of acquired knowledge; understanding the value of an adequate assessment of one's own achievements and capabilities;

cognitive: the ability to analyze and evaluate the impact of environmental factors, risk factors on health, the consequences of human activities in ecosystems, the impact of one's own actions on living organisms and ecosystems; focus on continuous development and self-development; ability to work with various sources information, convert it from one form to another, compare and analyze information, draw conclusions, prepare messages and presentations.

Regulatory: the ability to organize independently the execution of tasks, evaluate the correctness of the work, reflection of their activities.

Communicative: formation communicative competence in communication and cooperation with peers, understanding the characteristics of gender socialization in adolescence, socially useful, educational and research, creative and other activities.

Technologies : Health saving, problematic, developmental education, group activities

Activities (elements of content, control)

Formation of students' activity abilities and abilities to structure and systematize the studied subject content: teamwork- study of the text and illustrative material, compilation of the table "Systematic groups of multicellular organisms" with the advisory assistance of expert students, followed by self-examination; pair or group performance laboratory work with the advisory assistance of a teacher with subsequent mutual verification; independent work on the studied material.

Planned results

subject

understand the meaning biological terms;

describe the features of the structure and the main processes of life of animals of different systematic groups; compare the structural features of protozoa and multicellular animals;

recognize organs and systems of organs of animals of different systematic groups; compare and explain the reasons for similarities and differences;

to establish the relationship between the features of the structure of organs and the functions that they perform;

give examples of animals of different systematic groups;

to distinguish in figures, tables and natural objects the main systematic groups protozoa and multicellular animals;

characterize the direction of evolution of the animal world; give evidence of the evolution of the animal world;

Metasubject UUD

Cognitive:

work with different sources of information, analyze and evaluate information, convert it from one form to another;

write a thesis different kinds plans (simple, complex, etc.), structure educational material, give definitions of concepts;

make observations, set up elementary experiments and explain the results obtained;

compare and classify, independently choosing criteria for the specified logical operations;

build logical reasoning, including the establishment of cause-and-effect relationships;

create schematic models highlighting the essential characteristics of objects;

identify possible sources of necessary information, search for information, analyze and evaluate its reliability;

Regulatory:

organize and plan your learning activities- determine the purpose of the work, the sequence of actions, set tasks, predict the results of the work;

independently put forward options for solving the tasks set, foresee the final results of the work, choose the means to achieve the goal;

work according to a plan, compare your actions with the goal and, if necessary, correct mistakes yourself;

own the basics of self-control and self-assessment for making decisions and making a conscious choice in educational and cognitive and educational and practical activities;

Communicative:

listen and engage in dialogue, participate in a collective discussion of problems;

integrate and build productive interaction with peers and adults;

adequately use speech means for discussion and argumentation of one's position, to compare different points point of view, argue your point of view, defend your position.

Personal UUD

Formation and development of cognitive interest in the study of biology and the history of the development of knowledge about nature

Receptions: analysis, synthesis, conclusion, transfer of information from one type to another, generalization.

Basic concepts

Diversity of mammals, division into orders; general characteristics of units, the relationship of lifestyle and external structure. The importance of mammals in nature and human life, the protection of mammals.

During the classes

Knowledge update ( concentration of attention when learning new material)

Choose the correct answer in your opinion.

1. What common feature in all vertebrates?

the presence of a spine

habitation air-ground environment

multicellularity

2. Than brain protected vertebrates?

sink

shell

skull

3. How many types of vertebrates are there?

4. What is the special respiratory organ in fish?

leather

5. What are the respiratory organs of amphibians?

lungs and skin

6. What vertebrates first appeared on earth?

reptiles

Amphibians

7. How do reptiles reproduce?

give birth to cubs

spawn

lay eggs

8. What distinguishing feature birds?

inhabit the air-ground environment

body covered with feathers

only they lay eggs

9. Which group of vertebrates is the most organized on earth?

mammals

10. How do mammals differ from other vertebrates?

feed babies with milk

breathe with lungs

warm-blooded

Learning new material(teacher's story with elements of conversation)

Mammals are monotremes: general characteristics, features and origins .

Amazing organisms that lay eggs and feed their young with milk are monotreme mammals. In our article, we will consider the systematics and features of the life of this class of animals. General characteristics of the class Mammals.

The class Mammals, or Beasts, includes the most highly organized representatives of the Chordata type. Their hallmark is the presence of mammary glands in females, the secret of which they feed their cubs. The external features of their structure include the location of the limbs under the body, the presence of hairline and various derivatives of the skin: nails, claws, horns, hooves

Most mammals are also characterized by the presence of seven cervical vertebrae, a diaphragm, exclusively atmospheric breathing, a four-chambered heart, and the presence of a cortex in the brain.

Subclass of the First Beasts. This subclass of Mammals includes a single order called Monotremes.. They got this name due to the presence of a cloaca. This is one opening into which the ducts of the reproductive, digestive and urinary systems open. All these animals reproduce by laying eggs. How can animals with such features be representatives of the class Mammals? The answer is simple. They have mammary glands that open directly to the surface of the body, since monotremes do not have nipples. Newborns lick it off their skin. Primitive features structures inherited from reptiles are the absence of the cortex and convolutions in the brain, as well as teeth, the function of which is performed by horny plates. In addition, their body temperature fluctuates within certain limits depending on its changes in the environment from +25 to +36 degrees. Such warm-bloodedness can be considered quite relative. The egg-laying of monotremes cannot be called real. It is often referred to as an incomplete live birth. The fact is that the eggs do not immediately exit the genital ducts of the animal, but linger there for a certain time. During this period, the embryo develops already by half. After leaving the cloaca, monotremes incubate eggs or carry them in a special leathery bag.

Mammals are monotremes: fossil species Paleontological finds of monotremes are rather few. They belong to the Miocene, Upper and Middle Pleistocene epochs. The oldest fossil of these animals is 123 million years old. Scientists have come to the conclusion that the fossil remains practically do not differ from modern species. Monotreme mammals, whose representatives are endemic, live only in Australia and on the adjacent islands: New Zealand, Guinea, Tasmania.

Echidnas First Beasts- represented by only a few species. The echidna is a monotreme mammal. Due to the fact that its body is covered with long hard needles, outwardly this animal resembles a hedgehog. In case of danger, the echidna curls up into a ball, thus protecting itself from enemies. The body of the animal is about 80 cm long, its front part is elongated and forms a small proboscis. Echidnas are nocturnal predators. During the day they rest, and at dusk they go hunting. Therefore, their eyesight is poorly developed, which is compensated by an excellent sense of smell. Echidnas have burrowing limbs. With the help of them and a sticky tongue, they extract invertebrates in the soil. Females usually lay a single egg, which they hatch in a skin fold.

prochidni These are also representatives of the class Mammals, detachment Monotremes. From their closest relatives, echidnas, they differ in a more elongated proboscis, as well as the presence of three fingers instead of five. Their needles are shorter, most of them hidden in the wool. But the limbs, on the contrary, are longer. Prochidnas are endemic to the island of New Guinea. The basis of the diet of these monotremes is earthworms and beetles. Like echidnas they catch them sticky long tongue, on which numerous small hooks are located.

Platypus. This animal seems to have borrowed its body parts from other representatives of this kingdom. The platypus is adapted to a semi-aquatic lifestyle. Its body is covered with dense thick hair. It is very rigid and practically impermeable. This animal has a duck's beak and a beaver's tail. The fingers have swimming membranes and sharp claws. In males, horny spurs develop on the hind limbs, into which ducts of poisonous glands open. For a person, their secret is not fatal, but it can cause severe swelling, first of a certain area, and then of the entire limb.

No wonder the platypus is sometimes called "God's joke". According to legend, at the end of the creation of the world, the Creator had unused parts from various animals. From them he created the platypus. It is not just an Australian endemic. This is one of the symbols of the continent, the image of which is found even on the coins of this state. This mammal hunts well in the water. But it builds nests and burrows exclusively on land. He swims at a considerable speed, and grabs his prey almost at lightning speed - within 30 seconds. Therefore, aquatic animals have very few chances to hide from a predator. Thanks to valuable fur, the number of platypus has been significantly reduced. On this moment hunting them is prohibited.

V.V. Latyushin, E. A. Lamekhova. Biology. 7th grade. Workbook to the textbook by V.V. Latyushina, V.A. Shapkin "Biology. Animals. 7th grade". - M.: Bustard.

Zakharova N. Yu. Control and verification work in biology: to the textbook by V. V. Latyushin and V. A. Shapkin “Biology. Animals. Grade 7 "/ N. Yu. Zakharova. 2nd ed. - M.: Publishing house "Exam"

Presentation Hosting

Characteristics of the detachment monotreme oviparous (Monotremata)

Monotremes are a small group of the most primitive living mammals. Females lay 1 or 2, rarely 3 eggs (typically great content yolk, the bulk of which is located at one of the poles of the egg). Hatching of young from eggs occurs with the help of a special egg "tooth" formed on a small ovoid bone. Young animals hatched from eggs are fed with milk. During the breeding season, a brood pouch can form on the belly of the female, in which the laid egg matures.

The sizes of single passers are small: the body length is 30-80 cm. They have a heavy build, short plantigrade limbs, specialized for digging or swimming. The head is small, with an elongated "beak", covered with a cornea. The eyes are small, the external auricles are barely visible or absent altogether. The body is covered with coarse hair and spines or soft thick fur. Vibrissae are absent. In the calcaneal region of the hind limbs there is a horny spur, which is especially strongly developed in males. The spur is pierced by a canal - a special duct associated with the so-called shin gland, the function of which is not entirely clear. Apparently, it has some significance in reproduction. It is also suggested (unconvincingly) that the secret of the shin gland is poisonous and the spur serves as a weapon of defense. Mammary glands are tubular. There are no real nipples, and the excretory ducts of the glands open separately from each other on two glandular fields of the female's belly.

The average body temperature is lower than that of other mammals (platypus on average 32.2°C, echidnas - 31.1°C). Body temperature can vary between 25° and 36°C. The bladder, into which the ureters flow, opens into the cloaca. The oviducts enter the cloaca separately (there is no vagina or uterus). The seeds are located in abdominal cavity. The penis is fixed on the ventral wall of the cloaca and serves only to remove sperm.

The skull is flattened. The front section is elongated. The cartilaginous skull and the ratio of bones in the roof of the skull are to a certain extent similar to reptiles. Skull roof with anterofrontal and posterior frontal bones; the presence of these bones in the roof of the skull is the only case among mammals. The tympanic bone has the form of a flattened ring that does not fuse with the skull. The bony auditory meatus is absent. The malleus and incus in the middle ear fuse together and have a long process (processus folii). The lacrimal bone is absent. The zygomatic bone is greatly reduced in size or absent. Only monotremes among all mammals have a pre-vomer (praevomer). The premaxilla has a process similar to that of reptiles (processus ascendus); this is the only case among mammals. The articular fossa for the lower jaw is formed by the squamous bone. The lower jaw has only two weakly expressed processes - coronal and angular.

Teeth are present only in young animals or are completely absent. The shape of the teeth to a certain extent resembles the shape of the teeth of the Mesozoic Microleptidae. The skeleton of the forelimb girdle is characterized by a coracoid (coracoideum) and a procoracoid (procoracoi-deum) that are unique among mammals. In the presence of these bones, the similarity of the shoulder girdle of monotremes with the shoulder girdle of reptiles is manifested. Sternum with large breastplate (episternum). The clavicle is very large. Blade without comb. The humerus is short and powerful. The ulna is much longer than the radius. The wrist is short and wide. The fore and hind limbs are five-fingered. Fingers end in claws. In the pelvic girdle of males and females there are so-called marsupial bones (ossa marsupialia), which are attached to the pubic bones. Their function is unclear. The symphysis of the pelvic bones is greatly elongated. The proximal tibia with a large flattened process (peronecranon).

The spinal column consists of 7 cervical, 15-17 thoracic, 2-3 lumbar, 2 sacral, 0-2 coccygeal and 11-20 caudal vertebrae (Fig. 1).

Rice. 1.

The whole body is covered with a highly developed layer of subcutaneous muscles (rap-niculus carnosus). Only in the region of the head, tail, limbs, cloaca and mammary glands, the subcutaneous muscles are not developed. The lower jaw has a musculus detrahens attached to it. inside; this is the only case in mammals. The larynx is primitive and does not have vocal cords.

The brain is generally large, has mammalian features, but retains a number of reptilian features. Large hemispheres with numerous, sometimes few furrows. The structure of the cerebral cortex is primitive. Olfactory lobes are very large. The cerebellum is only partially covered by the cerebral hemispheres. The corpus callosum (corpus callosum) is absent; it is presented only as commissura dorsalis. The sense of smell is highly developed. Jacobson's organ is well developed. The structure of the hearing organs is primitive. Eyes with or without nictitating membrane. The sclera has cartilage. The vascular membrane is thin. Musculus dilatatorius and Musculus ciliaris are absent. The retina has no blood vessels.

The brain of platypuses is devoid of furrows and convolutions and, according to the plan of functional organization, resembles the brain of an echidna. Motor and sensory projections do not overlap all the way, while visual and auditory projections in the occipital pole of the cortex overlap with each other and partially with the somatic projection. Such an organization of the neocortex of the platypus, approaching the cortical plate of reptiles, allows it to be considered as even more primitive in comparison with echidnas.

Consequently, the brain of monotremes still retains many features of the brain of reptiles and at the same time differs from the latter in the general plan of structure characteristic of mammals.

The salivary glands are small or large. The stomach is simple, without digestive glands, which is the only case in mammals. Its function appears to be food storage, similar to that of the crop of birds. The digestive tract is divided into small, large intestines, there is a caecum. The intestines open into the cloaca, which is present in both sexes. The liver is multilobed, with gallbladder. The heart of monotremes has a structure characteristic of mammals, however, it also retains some reptile-like features, which consist, for example, in the fact that the right atrioventricular opening is equipped with only one valve.

Monotremes live in forests different type, in the steppes, overgrown with shrubs, on the plains and in the mountains, rising up to 2.5 thousand meters above sea level. They lead a semi-aquatic (platypus) or terrestrial (echidna) lifestyle; twilight and nocturnal activity; feed on insects and aquatic invertebrates. Life expectancy up to 30 years. Distributed in Australia, Tasmania, New Guinea.

Modern monotremes in their characteristics, compared with all other modern mammals, are closest to reptiles. However, they are not the ancestors of marsupials or placental mammals, but represent a separate specialized branch in the evolution of mammals. Fossil remains of representatives of the monotreme order are known only from Australia. The most ancient finds date back to the Pleistocene and do not differ significantly from modern forms. There are two possible theories explaining the origin of the monotremes. According to one of them, monotremes developed independently and in complete isolation from other mammals, starting from early period the emergence of mammals, perhaps from their reptile-like ancestors. According to another theory, a group of monotremes separated from the ancient marsupials and acquired its features due to specialization, retaining a number of features characteristic of marsupials, underwent degeneration and, possibly, to a certain extent, returned to the forms of their ancestors (reversion). The first of the theories seems more plausible. Significant differences in morphology between echidnas and platypus emerged in a relatively short period of time - starting from the upper Eocene. Echidnas are secondary land mammals, separated from the ancient aquatic platypuses.