The external structure of mammals. Lesson summary "general characteristics and features of the external structure of mammals" System of excretory organs

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FEDERAL EDUCATION AGENCY

STATE EDUCATIONAL INSTITUTION

HIGHER PUBLIC EDUCATION

"NOVOSIBIRSK STATE PEDAGOGICAL UNIVERSITY"

FACULTY OF ELEMENTARY CLASSES

Discipline: Zoology

Structural and behavioral features of mammals

Performed:

Elena Vaschenko

Novosibirsk 2010

Introduction

1. Common features of mammals

1.2 Features of the structure of mammals

2. Features of the behavior of mammals

2.2 Interspecies aggression

2.3 Intraspecific aggression

Conclusion

Bibliographic list

INTRODUCTION

Zoology - a scientific discipline that studies the animal world, a major component of biology. According to the objectives of the study, zoology is divided into a number of disciplines: taxonomy, morphology, embryology, animal genetics, zoogeography, etc. Protozoology, which studies protozoa, invertebrate zoology and vertebrate zoology, are distinguished according to the research objects. The last object of research and refers theriology, studying mammals.

The emergence of mammals became possible as a result of the formation of a number of large aromorphoses, which reduced the dependence of animals on changes in the external environment. Mammals evolved from ancient reptiles at the very beginning of the Mesozoic era, i.e. earlier than birds, but the development that led to the modern richness of the forms of this class of vertebrates dates back to the Cenozoic era, after the extinction of large reptiles.

I decided to talk about mammals, because it is the most highly specialized group of land animals. Currently, there are over 4,000 species of mammals.

In the first chapter of the abstract, I will give an overview of the general features of mammals that distinguish them from other animals, then I will describe the features of their structure and behavior. I will dwell on the features of the behavior of mammals in more detail, because this topic is very interesting and exciting, but it is not covered in the biology textbook.

1. GENERAL MAMMAL FEATURES

Mammals - warm-blooded vertebrates from the amniote group. As I said, this is the most highly specialized group of land animals, which is distinguished by the following progressive traits.

1. Highly developed central nervous system and sensory organs... The cortex of the cerebral hemispheres, formed by the gray matter, appears, which provides a high level of nervous activity and complex adaptive behavior.

2. Thermoregulation system, providing relative constancy of body temperature.

3. Viviparity(except for oviparous ones) and feeding the cubs with mother's milk, which ensures the best safety of the offspring.

Mammal organization height it is also expressed in the fact that all organs in them achieve the greatest differentiation, and the brain is of the most perfect structure. The center of higher nervous activity is especially developed in it - the cerebral cortex, consisting of the gray medulla. Concerning reactions and behavior of mammalsandare of exceptional perfection... This is facilitated by very complex senses, especially hearing and smell. The rapid progressive development of mammals was also facilitated by the differentiation of teeth into incisors, canines and molars.

A huge role in the development of this group was played by the acquisition warmaboutblood, that is, a constantly high body temperature. It arises due to: a) unmixed blood circulation, b) enhanced gas exchange, c) thermoregulatory devices

Unmixed circulation, like in birds, is achieved by a four-chambered heart and in animals only one (left) aortic arch is preserved. The acquisition of the alveolar structure of the lungs and the appearance of the diaphragm led to increased gas exchange. Diaphragm- This is a muscular septum that completely divides the body into two parts - chest and abdominal. The diaphragm is involved in the act of inhaling and exhaling. Thermoregulation achieved by the appearance of hair and skin glands

Due to the perfection of the digestive, respiratory and circulatory systems, the entire metabolism of mammals is very intensive, which, along with a high body temperature, makes them less dependent on the climatic conditions of the environment than amphibians and reptiles. The rapid progressive development of animals is also due to the fact that the highest of them have developed a live birth. The nutrition of the embryo in the womb is carried out through a special organ - the placenta. After birth, the cub is fed with milk. It is secreted by special mammary glands. All this greatly increases the survival rate of the offspring.

Thanks to the height of organization and perfect psyche, mammals by the beginning of the Cenozoic era (65 million years ago) were able to displace the reptiles that had dominated on Earth until then and occupied all the main habitats.

2. CCASTRUCTURE BENEFITS OF MAMMALS

External structure

In animals they are well expressed.: head, neck, torso and tail. On the head usually distinguish between the cranial region, located behind the eyes, and the facial, or muzzle, located in front. Eyes equipped with upper, lower and third eyelids. Unlike birds, the nictitating membrane (third eyelid) covers only half of the mammalian eye. On the sides of the head are large ears, at the end of the muzzle are paired nostrils. Mouth bordered with fleshy lips characteristic of mammals. There are usually very coarse hairs on the upper lip - vibrissae. Several of them are located above the eyes. They play the role of additional organs of touch. Under the root of the tail is the anus, and a little anterior to it - the urogenital. In females, 4-5 pairs of nipples are located on the sides of the body on the ventral side. The limbs are five or four-fingered, the fingers are armed with claws.

Skin

Wool, covering the body of mammals, is a derivative of the skin. There are two kinds of hair - guard and soft - down. The skin is made up of two main layers - epidermis and corium. The first is a thin stratum corneum, and the second is very thick, dense. The lower part of it forms the subcutaneous tissue.

Skeleton

The spine consists of five sections: cervical, thoracic, lumbar, sacral and caudal. The vertebrae have flat articular surfaces characteristic of mammals and are separated by round cartilaginous discs - menisci.

The cervical region in all mammals (with very rare exceptions) contains 7 vertebrae. (Both the mouse and the giraffe have 7 cervical vertebrae). These vertebrae lack free ribs. The thoracic region contains 12-13 vertebrae, all of which are provided with ribs. The front seven pairs of ribs are connected to the sternum and are called "true ribs". The next five pairs do not reach the sternum. The lumbar spine is devoid of ribs and usually contains 6-7 vertebrae. The sacral region is formed in most mammals by four fused vertebrae. The anterior ones usually carry two processes, with the help of which the pelvis is attached. The caudal region is very variable in the number of vertebrae.

Skull it is divided into axial, consisting of the bones surrounding the brain, and visceral (facial), which includes the bones surrounding the oral opening - the palate, bones of the upper and lower jaws.

Shoulder girdle represented only by the scapula and clavicle, and the crow's bone (coracoid) in mammals is not. In fast runners, the collarbone (ungulates) usually disappears as well. The pelvic region consists of a pair of nameless bones, each of which is formed by the fusion of the ilium, ischium, and pubic bones. The paired limb skeleton has three typical sections. In the forelimbs, this is the shoulder, forearm and hand, and in the hind limbs, the thigh, lower leg and foot. In mammals, a rounded tendon bone appears on the hind limbs at the knee joint - the patella.

Muscular system

This system in animals reaches exceptional development and complexity. They have several hundred individual striated muscles. A feature of the muscular system of mammals is the presence of a diaphragm and the appearance of subcutaneous muscles. Diaphragm- This is a domed muscular septum that separates the thoracic region from the abdominal. In the center, it is perforated by the esophagus. The diaphragm takes part in the acts of respiration and excrement of animals. The subcutaneous musculature is a continuous subcutaneous layer. With its help, animals can move skin areas. The same muscles take part in the formation of the lips and cheeks. In monkeys, it almost disappeared and remained only on the face. There she received an unusually strong development - this is the so-called facial muscles.

Nervous system

Brain the beast has powerfully developed hemispheres of the forebrain and cerebellum. They cover all other parts of the brain from above.

Forebrain consists of cerebral hemispheres covered with a gray medulla - the cerebral cortex. The olfactory lobes move forward from the hemispheres. A wide jumper of white nerve fibers is located between the hemispheres.

Diencephalon has a funnel and a crossover of the optic nerves, as in other classes of vertebrates. The pituitary gland is attached to the funnel of the diencephalon, while the pineal gland is located above the cerebellum on a long stem. Midbrain differs in very small size, in addition to the longitudinal groove, it also has a transverse groove, which is characteristic only of mammals. Cerebellum consists of an unpaired part - a worm and two lateral ones, which are very large and are usually designated as cerebellar hemispheres. Medulla has a feature that is also characteristic only of mammals. On the sides of this brain, bundles of nerve fibers are isolated, going to the cerebellum. They are called the hind legs of the cerebellum. The medulla oblongata passes into the spinal cord.

Sense organs

They are very developed in mammals, and, in accordance with the ecological specialization of a particular group, the leading role is played by smell, sight, hearing, or touch. The hearing organs in animals are especially well developed. They have bony auditory drums and large, movable outer ears.

Digestive organs

Oral cavity limited by the lips of animals. The lips take part in grasping and holding prey. The oral cavity is bounded from above by a hard bony palate. Due to this, the choanas (internal nostrils) are pushed back towards the pharynx. This allows the animals to breathe while the food is in the mouth. The sides of the oral cavity are bounded by soft, muscular cheeks, and at the bottom of the mouth is a large muscular tongue. Its functions are to perceive taste and push food while chewing under the teeth and down the throat while swallowing. The ducts of the salivary glands open into the mouth (4 paired glands - parotid, infraorbital, submandibular and sublingual). Teeth do not adhere to the surface of the bone, as in the previous classes, but sit in independent cells. The teeth are differentiated into incisors, canines and molars. The tooth itself consists of parts such as a crown with a working surface, the body of the tooth and its root. Throat of beasts short, the windpipe and choanae open into it. Thus, in mammals, the pharynx is the intersection of two pathways - food and respiratory. Esophagus is a simple, highly extensible muscular tube. After passing through the diaphragm, it connects to the stomach. Stomach looks like a large horseshoe-shaped curved bag that lies across the body. A fat-filled peritoneum hangs from the stomach, which covers all internal organs with an apron. Liver located under the diaphragm, its flows open into the duodenum, in the loop of which the pancreas lies. Most mammals have a gallbladder. Intestines It can be of different lengths, it depends on the composition of the feed. The herbivorous rabbit has a very long intestine - 15-16 times longer than the body. Its divisions are the small, large and rectum. At the beginning of the large intestine, mammals have an unpaired cecum - the cecum. The intestine opens outward with an independent anal opening.

Respiratory system

Larynx, as usual for mammals, has cricoid cartilage, in front of which is a large thyroid cartilage. The mammalian larynx is complex. On the inside of the larynx, the vocal cords are stretched. These are paired elastic folds of the mucous membrane, stretched in the laryngeal cavity and limiting the glottis. Lungs represent a pair of spongy bodies hanging freely into the chest cavity. Their internal structure is characterized by great complexity. The trachea near the lungs is divided into two bronchi. The bronchi, entering the lungs, are divided into secondary bronchi, which, in turn, are divided into bronchi of the third and fourth order. They end with bronchioles. The ends of the bronchioles are swollen and braided with blood vessels. These are the so-called alveoli, where gas exchange takes place.

Circulatory system

A heart animals, like birds, are four-chambered, and the left ventricle drives blood through a large circle of blood circulation and, like birds, has much thicker walls than the right one. A large vessel departs from the left ventricle - the aorta, which begins the systemic circulation. All organs of the body are supplied with arterial blood, and venous blood is collected through the vein system. The largest of them - the posterior and two anterior vena cava - flow into the right atrium. From the right atrium, blood enters the right ventricle, from here begins a small circle of blood circulation, or, as it is also called, pulmonary. Venous blood is expelled from the right ventricle into the large pulmonary artery. This artery divides into right and left, leading to the lungs. From each lung, blood is collected in the pulmonary vein (blood in it is arterial), both veins merge and flow into the left atrium. Further, from the left atrium, blood is poured into the left ventricle and again goes through a large circle of blood circulation.

Organs, secretions

Have mammals are a pair of bean buds located in the lumbar region. From the inner concave side of each kidney, there is a ureter (thin tube) that flows directly into the bladder. The bladder opens into the urethra.

Genitals

In mammals, these are paired testes (in males) or paired ovaries (in females). Testes have a characteristic oval shape. The appendages of the testes are adjacent to them. Paired vas deferens open at the beginning of the urethra. The end parts of the vas deferens are expanded into seminal vesicles. The paired ovaries of the female have an oval-flattened shape. An oviduct is located near each ovary. At one end, the oviduct opens into the body cavity, and with the opposite end, without a visible border, it passes into the uterus. The uterus in animals is two-horned, the right and left horns of the uterus open independently into the vagina. It is unpaired. With its rear end, it gradually passes into the urethra and the bladder opens into it. Outside, the vagina opens with the urogenital opening.

Embryo development

Egg cells develop in the ovary, then mature cells, upon exiting the ovary into the body cavity, are trapped there by the funnel of the oviduct. Due to the ciliated movements of the cilia of the tube (oviduct), the egg moves along it, and if the female is fertilized, then in the tube (usually in the first third of it), the egg merges with the sperm. The fertilized egg continues to slowly descend into the uterus and at the same time begins to break up (division of the egg into many cells). Having reached the uterus, the egg, which by that time had turned into a dense multicellular ball, is introduced into the wall. There, nutrients begin to flow to it. Pretty soon, a placenta forms around the embedded embryo. This is the shell of the fetus, very characteristic of mammals. The placenta is a spongy organ rich in blood vessels, in which the child and maternal parts are distinguished. The nursery consists of the villi of the embryonic membrane, and the mother's - of the wall of the uterus. During childbirth, the muscular layer of the uterus is greatly reduced and the children's placenta (chorion), by that time connected very slightly to the mucous membrane of the uterus, opens and goes out together with the newborn in the form of a child's place.

3. OSOBMAMMAL BEHAVIORALITY

Intraspecific behavior in mammals is characterized by aggression. It is due to the protection of the species from external and intraspecific factors. Aggressive behavior often manifests itself already in the early stages of ontogenesis, which can lead to the destruction of the youngest cub (kainism), and sometimes to being eaten by its fellows (cannibalism). On the basis of aggressive behavior, infanticide (infanticide) is also possible in predatory mammals (lions), rodents (ground squirrels), etc. When protecting a group territory, there is a collective aggressive behavior of the hosts towards strangers. In many cases, aggressive behavior is stimulated by sex hormones. Under the influence of aggressive influences, the body experiences a state of tension, stress (English stress - tension). With moderate stress, an increase in the activity of the autonomic nervous system is found. Stimulation of the adrenal medulla through the autonomic nerves causes them to release adrenaline into the bloodstream. At the same time, changes occur in various parts of the body. The secretion of sweat glands begins, the coat stands on end, the heart beats faster, breathing becomes more frequent and deeper, blood from the digestive tract is redirected to the muscles. All this prepares the body for energetic actions of the required type. Under the influence of chronic stress, the animal becomes sick and may die.

The forms of aggression are diverse, we will try to classify them.

3.1 Interspecies aggression

1. Aggressiveness of the predator towards the prey

In nature, some species inevitably attack others. The mutual influence of predator and prey leads to evolutionary competition, forcing one of them to adapt to the development of the other. But, it is worth noting that the predator never completely destroys the prey population, some balance is always established between them. Strictly speaking, ethologists generally do not consider the behavior of a predator to be aggressive (Lorenz, Dolnik, etc.) or consider it a special form of aggression that differs from all others. “When a wolf catches a hare, it’s not aggression, but hunting. Likewise, when a hunter shoots ducks or a fisherman catches fish, it is not aggressive behavior. After all, they all have no hostility, no fear, no anger, no hatred towards the victim. " AK. Lorenz writes: “The internal origins of the behavior of the hunter and the fighter are completely different. When a lion kills a buffalo, this buffalo causes no more aggressiveness in him than in me an appetizing turkey hanging in the pantry, which I look at with the same pleasure. The difference in internal motives is clearly visible already in the expressive movements. If a dog chases a hare, then it has exactly the same tenseness - a joyful expression with which it greets the owner or anticipates something pleasant. And on the lion's face, at the dramatic moment of the jump, you can quite clearly see, as recorded in many excellent photographs, that he is not angry at all. Growling, flattened ears and other expressive movements associated with combat behavior can be seen in hunting predators only when they are seriously afraid of their armed prey, but in this case only in the form of a hint. "

A remarkable illustration of all that has been said is an excerpt from the novel by J. London "White Fang", where a wolf cub, having just finished off partridge chicks, engages in a fight with a mother partridge. “… He was met by a winged whirlwind. The rapid onslaught and the furious blows of the wings blinded and stunned the wolf cub. He buried his head in his paws and screamed. The blows rained down with renewed vigor. The mother partridge was beside herself with rage. Then the wolf cub got angry. He jumped up with a growl and began to fight back with his paws, then he thrust his small teeth into the wing of the bird and began to pull and drag it from side to side with all his strength. The partridge was torn, striking him with the other wing. It was the wolf cub's first fight. He was jubilant. He forgot all his fear of the unknown and was no longer afraid of anything. He tore and beat a living creature that was hitting him. Moreover, this living thing was meat. The wolf cub was seized by a lust for blood. He was too absorbed in the fight and too happy to feel his happiness ... ".

2. a) Much closer to true aggression than the attack of the hunter on the prey, the opposite case of the counterattack of the prey against the predator. Attacking a predator-eater makes obvious sense for the preservation of the species. Even when the attacker is small, he causes the target of the attack very sensitive trouble. This is especially true of herd animals, which all en masse attack the predator (the so-called mobbing). There are many examples. Ungulates often form a dense ring, pushing their horns forward and protecting cubs. Musk oxen so repel the attacks of wolves, buffaloes defend themselves from lions. In our domestic cows and pigs, the instinct of a general attack on a wolf sits firmly in the blood.

2.b)Like a predator attacking prey or baiting a chiunickname his victims, the species-preserving function of the third type of combat behavior, which Lorenz called critical reaction, is also obvious. The expression "fight like a rat cornered" symbolizes a desperate struggle in which the fighter puts everything, because he can neither leave nor count on mercy. This form of combat behavior, the most violent, is motivated by fear (aggression and fear are twins), the strongest urge to escape, which cannot be realized because the danger is too close. The animal, one might say, no longer risks turning its back on it - and attacks itself, with "the courage of despair." This is what happens when escape is impossible due to space constraints - as in the case of a trapped rat - but the need to protect the brood or family can also work. An attack by the mother on any object that gets too close to the cubs should also be considered a critical reaction. When a dangerous enemy suddenly appears within a certain critical zone, many animals violently attack him, although they would run from a much greater distance if they noticed his approach from afar.

In addition to these special cases of interspecific struggle, there are others, less specific. Any two animals of different species, approximately equal in strength, can grapple because of food, shelter, etc. In all the above cases of struggle between animals, there is a common feature: it is quite clear here what benefit each of the participants in the battle gets for the preservation of the species. But intraspecific aggression (aggression in the narrow and unique sense of the word) also serves to preserve the species, although this is not so obvious.

3.2 Intravenousidol aggression

1. Territorial aggression(aggression aimed at protecting the territory)

Active defense- an essential feature of territorial behavior. Aggressiveness manifests itself in relation to any representative of the same species, especially of the same sex. It reaches its maximum at the beginning of the breeding season, when the territories are just being established. The territory should not be thought of as a well-defined space with precisely defined boundaries (it can be temporary). As a rule, this zone is determined only by the fact that the readiness of a given animal to fight is highest in the place most familiar to it, namely, in the center of its area. That is, the threshold of aggressiveness is lowest where the animal feels most confident, where its aggression is least suppressed by the desire to flee. With distance from this "headquarters" combat readiness decreases as the situation becomes more alien and fearsome. As one approaches the center of the habitat, aggressiveness increases exponentially. This increase is so great that it compensates for all differences in size and strength that can be found in mature adults of the same species.

When the defeated one takes flight, one can observe a phenomenon that occurs in all self-regulating systems with inhibition, namely, oscillations. The pursued - as he approaches his headquarters - courage reappears, and the pursuer, having penetrated into enemy territory, loses courage. As a result, the fugitive suddenly turns around and - as suddenly as vigorously - attacks the recent winner, who is now beaten and driven away. All this is repeated several more times, and, in the end, the fighters stop at a very definite point of balance, where they only threaten each other.

This simple mechanism of struggle for territory ideally solves the problem of "fair", that is, the most beneficial for the entire species in its entirety, distribution of individuals over the area in which this species can live. At the same time, the weaker ones can feed themselves and give offspring, albeit in a more modest space.

Animals can achieve the same effect without aggressive behavior, simply by avoiding each other. "Terrain marking" plays an important role here, especially at the periphery of the site. Feces, secretions of skin glands, optical signs - bark ripped from tree trunks, trampled grass, etc. Mammals for the most part "think with their nose", so there is nothing surprising in the fact that they have a very important role in marking their possessions with smell. Many mammals leave odor signals where they meet or expect to meet a rival. Dogs urinate for this purpose, hyenas, martens, chamois, antelopes and other species use special glands, the secrets of which they mark the soil, shrubs, stumps, stones, etc. The brown bear scratches its back against a tree while urinating. Although behind such marks there is already a silent threat of aggression.

Fight for territory is a very important function of males. A family or herd cannot exist without good land; the prosperity of a group depends on their quantity and quality. Possessions need to be constantly trying to expand, including at the expense of neighboring groups. Therefore, clashes over territories are inevitable. Human ancestors also lived in territorial groups, and for them the struggle for territory was inevitable. Territorial wars for some tribes became the main occupation in life.

So, taking into account the above, it can be considered reliable that the uniform distribution of animals of the same species in space is the most important function of intraspecific aggression. In addition, Menning highlights another aspect of territorial behavior. Interestingly, in territorial animals, the first reaction of a male to a female contains elements of attack and flight. This aggressiveness is very important in the formation of "couple attachment". This aggression, although it can occur between a male and a female, is largely redirected outward to neighboring animals. Often the male attacks the male, and the female attacks the female. The cooperation of the male and the female in the defense of the territory strengthens the connection between them.

2. Mating tournaments

A certain category of individuals is always engaged in mating battles. In most cases, males fight, attacking exclusively or mainly on other males of their own species. Sometimes both the male and the female fight, and when this happens, the male attacks another male, and the female attacks another female. Different species fight in different ways. First of all, differently used weapons. Dogs bite each other, horses and many other ungulates try to kick the opponent with their front limbs. Deer measure their strength by grappling with their horns. What are these collisions for? Charles Darwin already noted that sexual selection - the selection of the best, most powerful animals for procreation - is largely determined by the struggle of rival animals, especially males. The power of the father provides immediate advantages to the offspring in those species where the father is actively involved in the care of the children, primarily in their protection. The close connection between males' care for offspring and their fights is most clearly manifested in those animals that are not territorial in the above sense of the word, but lead a more or less nomadic lifestyle, such as large ungulates, land monkeys, etc. These animals have an intraspecific aggression does not play a significant role in the distribution of space; in the dispersal of species such as bison, various antelopes, horses that gather in huge communities and for which the division of sites and the struggle for territory are completely alien, because they have enough food. However, the males of these animals fight each other fiercely and dramatically, and the selection resulting from this struggle results in large and well-armed family defenders. Thus, such impressive fighters as bulls of buffalo or males of large baboons arise.

In this regard, it is necessary to mention one more fact - purely intraspecific selection can lead to the appearance of not only traits that are useless in the sense of adaptation to the environment, but also directly harmful to the conservationeview. Deer antlers, for example, have evolved exclusively for duels; these antlers are not suitable for anything else. Deer protect themselves from predators only by their front hooves. Similar signs develop in cases where selection is directed only by the competition of congeners, without connection with the non-species environment. Returning to the topic of the importance of a duel for preserving a species, we can say that it serves as a useful selection only where fighters are tested not only by intraspecific dueling rules, but also by fights with an external enemy. The most important function of the duel is the choice of the family's fighting defender, thus, another function of intraspecific aggression is to protect the offspring. The proof is the fact that in many animals, in which only one sex takes care of the offspring, representatives of this particular sex are really aggressive towards their relatives, or their aggressiveness is incomparably stronger. Something similar is observed in humans.

4. BUTgression in the community of social animals, leading to mouthbutrenewal of the hierarchy

Hierarchy- this is the principle of organization, without which, obviously, the ordered joint life of higher animals cannot develop. It consists in the fact that each of the individuals living together knows who is stronger than himself and who is weaker. In the group, a dominance-subordination relationship is established, while the number and fierceness of collisions decreases, because everyone can retreat without a struggle before the stronger - and can expect that the weaker in turn will retreat in front of him if they get in each other's path. Dolnik emphasizes that the victory in skirmishes does not necessarily go to the one who is stronger. It is given to the one who is more aggressive: he likes to impose conflicts, threatens a lot and skillfully, and he himself relatively easily withstands other people's threats. So, the individual that wins most often becomes the dominant. Inevitably, there comes a moment when the dominant takes out anger at the subdominant (due to a spontaneous outburst of aggression). He will not answer him, but redirect the aggression to the one below on the hierarchical ladder (after all, it is scary to touch the dominant). By redirecting, aggression will reach the one standing at the lowest level. There is no one to take out aggression against, and it often accumulates. In a large group, a dominant is always at the top, but there may already be two or three subdominants. This is how a hierarchical pyramid is formed, the lower layer of which consists of individuals who give in to everyone. They have accumulated a lot of unrealized aggressiveness, hidden by ingratiating behavior in front of their superiors. This is a law of nature and it is impossible to resist it.

Dog-headed monkeys - baboons, hamadryas and others - form hierarchical pyramids by age. At the head of the group are several elderly males with the greatest power and responsibility for the safety of the group (gerontocracy). But, younger males can unite in alliances and attack higher individuals. These alliances are not strong, though, because monkeys betray each other all the time, especially when it comes to fighting. Thus, unions can change the hierarchical pyramid through "revolution from below". The formation of a pyramid by age is also characteristic of humans. In traditional societies, the age hierarchy is very strict. But the formation of alliances of subordinates in order to overthrow the dominants is also a common thing, known from antiquity to the present day.

The wide spread of the hierarchy convincingly testifies to its important species-preserving function: thus, unnecessary struggle between members of the community is avoided. Here the question arises: how is this better than a direct prohibition of aggression towards members of the community? Ethologists argue that it is impossible to avoid aggression. Firstly, often a community (a pack of wolves or a herd of monkeys) desperately needs aggressiveness towards other communities of the same species, so fighting should be excluded only within the group. Secondly The tensions that arise within a community as a result of aggressive impulses and the hierarchy that grows out of them can give it a largely useful structure and strength. The further apart the ranks of two animals, the less hostility between them. And since superior individuals (especially males) necessarily intervene in the conflicts of inferior ones, the principle “The place of the strong is on the side of the weak!” Is triggered.

Age hierarchy arose also not by chance. With the general progress of evolution, the role of the experience of old animals increases more and more; we can even say that the joint social life of the most intelligent mammals acquires a new function in the preservation of the species due to this, namely, the traditional transfer of individually acquired information. Naturally, the opposite is also true: shared social life produces selective pressure towards better development of learning abilities, since these abilities in social animals benefit not only the individual, but also the community as a whole. Thus, a long life, significantly exceeding the period of sexual activity, acquires value for the preservation of the species.

CONCLUSION

In the first chapter of the abstract, I examined the main features of the progressive evolution of mammals, which helped them become the dominant animals on the planet. These are three main groups of adaptations: associated with constant high body temperature; associated with the peculiarities of breeding and raising cubs; associated with the large brain in animals of this group. The structure and physiology of animals and their modern taxonomy are also considered.

In the second chapter, I examined the features of the behavior of mammals, in particular, interspecific and species aggression. It has been proven that life without aggression is impossible, even if you create an ideal environment that does not contain any irritants. With prolonged non-fulfillment of any instinctive action (manifestation of aggression), the threshold of irritation decreases. A decrease in the threshold of irritation can lead to the fact that, under special conditions, its value can fall to zero, that is, the corresponding instinctive action can "break through" without any external stimulus. In principle, every truly instinctive action, which is deprived of the possibility of discharge, brings the animal into a state of general anxiety and forces it to search for a discharging stimulus. A decrease in the annoying threshold and search behavior, rarely in any cases, are manifested as clearly as in the case of aggression.

The benefits of aggression can be considered proven. Living space is distributed between animals in such a way that, whenever possible, everyone finds food for themselves. For the benefit of the offspring, the best fathers and the best mothers are chosen. Children are protected. The community is organized in such a way that a few wise males have enough authority to ensure that the decisions needed by the community are not only made, but carried out. The goal of aggression is never to destroy a relative, although, of course, an accident can occur during a fight when a horn gets into an eye or a canine tooth into the carotid artery. Aggression is not at all a destructive principle, it is only a part of the organization of all living beings, preserving their system of functioning and their very life. Like everything in the world, she can make a mistake - and at the same time destroy life. However, in the great accomplishments of the formation of the organic world, this force is destined for good.

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Features of the structure of mammals

The structure of mammals	Features of the structure of mammals
Body covers	Skin (strong and elastic, there are sebum and sweat glands); Hair cover (consists of coarse guard hair and soft thin hair of the undercoat, growing from hair follicles in the skin); Claws, nails, or hooves at the ends of the fingers
	1. Skull (brain and facial) 2. Spine - 7 cervical vertebrae; 12-15 thoracic (ribs are attached to them, connected in front with the sternum, forming a rib cage), 2-9 lumbar vertebrae, 3-4 sacral, caudal vertebrae (the number depends on the length of the tail) 3. Belt of the forelimbs (two shoulder blades and two collarbones) 4. Hind limb girdle (three pairs of fused pelvic bones) 5. Skeletons of the limbs (the structure depends on the living conditions)	1. Brain protection, food capture and chopping 2. Body support. 3. Connection of the forelimbs with the spine. 4. Connection of the hind limbs with the spine
	The muscles of the back, girdles of the limbs and extremities are especially developed.	Exercising various movements
Digestive system	Oral cavity (has teeth, tongue, salivary glands) - "pharynx -> esophagus -> stomach -" intestine (small and large sections and rectum, the ducts of the pancreas and liver flow into it) - "anus ...	Chopping, digesting food, absorbing nutrients into the blood
Respiratory system	Nasal cavities, larynx, trachea, two lungs. Breathing with the diaphragm.	Saturation of blood with oxygen, removal of carbon dioxide
Circulatory system	Four-chambered heart, two circles of blood circulation.	Metabolism of cells with blood.
Highlighting	Kidneys (one on each side of the body) - "ureters (from each kidney) -" bladder (one) - "urethra.	Removal of excess water and degradation products
Nervous system	1. Brain - on the cerebral hemispheres of the forebrain there is a cortex with convolutions (associated with a more complex behavior than other animals); well developed cerebellum (associated with the coordination of more complex movements) 2. Spinal cord.	Control of movements, unconditioned and conditioned reflexes; perception and transmission of signals
Sense organs	The degree of development of each of the senses depends on the lifestyle of the animal.
Behavior	Complex, reflexes are easily formed, providing quick adaptation to changing environmental conditions
Reproduction	All dioecious, most (except for oviparous ones) bear cubs in a special organ - the uterus, and the embryo is attached to the wall of the uterus by the placenta (through the umbilical cord). Pregnancy is the process of intrauterine development of the embryo. The cubs are fed with milk formed in the mammary glands (milk is a mixture of proteins, fats, carbohydrates, vitamins, mineral salts and water needed by the cub). Take care of the offspring.

The figure below shows the internal structure of mammals.

External structure

Skin

Skeleton

Muscular system

Nervous system

Brain the beast has powerfully developed hemispheres of the forebrain and cerebellum. They cover all other parts of the brain from above.

Sense organs

Digestive organs

Respiratory system

Circulatory system

Organs, secretions

Genitals

Embryo development

Zoology – a scientific discipline that studies the animal world, a major component of biology. According to the objectives of the study, zoology is divided into a number of disciplines: taxonomy, morphology, embryology, animal genetics, zoogeography, etc. Protozoology, which studies protozoa, invertebrate zoology and vertebrate zoology, are distinguished according to the research objects. The last object of research and refers t eriology, dealing with the study of mammals.

Common features of mammals

Mammals are warm-blooded vertebrates from the amniote group. As I said, this is the most highly specialized group of land animals, which is distinguished by the following progressive traits.

1. Highly developed central nervous system and sensory organs. The cortex of the cerebral hemispheres, formed by the gray matter, appears, which provides a high level of nervous activity and complex adaptive behavior.

2. The system of thermoregulation, which ensures the relative constancy of body temperature.

3. Viviparity (except for oviparous ones) and feeding of cubs with mother's milk, which ensures better safety of the offspring.

The height of organization of mammals is also expressed in the fact that all organs in them achieve the greatest differentiation, and the brain is of the most perfect structure. The center of higher nervous activity is especially developed in it - the cerebral cortex, consisting of the gray medulla. In this regard, the reactions and behavior of mammals reach exceptional perfection. This is facilitated by very complex senses, especially hearing and smell. The rapid progressive development of mammals was also facilitated by the differentiation of teeth into incisors, canines and molars.

A huge role in the development of this group was played by the acquisition of warm-bloodedness, that is, a constantly high body temperature. It arises due to: a) unmixed blood circulation, b) enhanced gas exchange, c) thermoregulatory devices. Unmixed blood circulation, as in birds, is achieved by a four-chambered heart and in animals only one (left) aortic arch is preserved. The acquisition of the alveolar structure of the lungs and the appearance of the diaphragm led to increased gas exchange. Diaphragm- This is a muscular septum that completely divides the body into two parts - the chest and abdominal. The diaphragm is involved in the act of inhaling and exhaling. Thermoregulation achieved by the appearance of hair and skin glands.

Features of the structure of mammals

External structure. In animals, they are well expressed: head, neck, body and tail. On the head, the cranial region, located behind the eyes, and the facial, or muzzle, located in front are usually distinguished. The eyes are equipped with an upper, lower and third eyelid. Unlike birds, the nictitating membrane (third eyelid) covers only half of the mammalian eye. On the sides of the head are large ears, at the end of the muzzle are paired nostrils.

Fig. 1. Diagram of the structure of mammals

1- skin; 2 - skull; 3 - spine; 4 - oral cavity; 5 - pharynx; 6 - esophagus; 7 - stomach; 8 - small intestines; 9 - large intestine; 10 - liver; 11 - kidneys; 12 - ureters; 13 - windpipe; 14 - lungs; 15 - heart; 16 - diaphragm; 17 - brain; 18 - spinal cord; 19 - sex gland

The mouth is bordered with fleshy lips characteristic of mammals. On the upper lip, there are usually very hard hairs - vibrissae. Several of them are located above the eyes. They play the role of additional organs of touch. Under the root of the tail is the anus, and a little anterior to it - the urogenital. Females have 4–5 pairs of nipples on the ventral side of the body. The limbs are five or four-fingered, the fingers are armed with claws.

Skin. The wool that covers the body of mammals is a derivative of the skin. There are two kinds of hair - guard and soft - down. The skin consists of two main layers - the epidermis and the corium. The first is a thin stratum corneum, and the second is very thick, dense. The lower part of it forms the subcutaneous tissue.

The hair represents the horny formation. In it, a lower expanded part - a bulb - and a long rod protruding outward are distinguished; its lower part, together with the bulb, forms a hair root that sits in a pouch. In the rod under the microscope, 3 layers of cells are visible: the cuticle, the middle layer and the core. Hair contains pigment, which determines its color. White hair coloration is sometimes associated with the presence of air inside the cells. In most animals, hair is divided into 2-3 main categories (Fig. 1).
Outside the fur, long guard hairs are visible, under them there is a thick and delicate underfur; often even longer guide hairs are visible among the awn. Hair is not arranged randomly, but in certain groups. The shape of individual hairs and the type of their distribution are characteristic for each type of animal.

Fig. 2. The structure of the skin and hair types of mammals (according to Geiler, 1960)

1 - underfloor; 2 - guard hair; 3 - stratum corneum of the epidermis; 4 - malpighian layer; 5 - corium; 6 - muscle of the hair follicle; 7 - sebaceous gland; 8 - hair root; 9 - hair papilla; 10 - blood vessel; 11 - sweat gland

A special modification of hair is represented by vibrissae, or tactile hair, located in groups on the face ("mustache", etc.), and sometimes on the paws and abdominal side of the body. Modifications of the hair cover also include the stiff bristles of a wild boar, porcupine quills, hedgehogs, etc. The hair cover plays a very important role in the life of animals: it protects them from the adverse effects of the environment, helps to regulate body temperature, and often disguises the animal. Hair (fur) reaches its best development in animals of cold and temperate climates. The emergence of hairline in the process of evolution turned out to be a very important adaptation that made it easier for animals to live in the most unfavorable landscapes for life.

The hairline develops with the age of the animal and is periodically replaced throughout the year. Moulting is usually seasonal, sometimes accompanied by a change in color. It is closely related to seasonal changes in meteorological conditions. In most of our land animals, winter hair is much thicker and more luxuriant than summer. So, on the back of a squirrel on a skin area of 10 mm 2, there are 46 hair groups in summer, and 89 in winter, that is, almost twice as many. The length of the guard hairs increases from 11 to 20 mm, the underfur increases from 7 to 12 mm. Seasonal dimorphism of the hairline is poorly expressed in burrowing, hibernating and aquatic animals.

Most species have 2 molts, but in some, their number reaches 3-4. The timing of the onset and duration of molting depend on meteorological conditions, sex, age, body condition of the animal and therefore change from year to year. But the order of the seasonal change of hair on certain parts of the body is natural and is generally preserved annually. In this case, usually spring and autumn molts occur in the reverse order (from head to tail and vice versa). The flesh on the shedding areas of the skin turns blue, which makes it easier to study the shedding process. In terrestrial animals, the change of hairline occurs in a relatively short time, especially in spring, and in aquatic and semi-aquatic animals it is strongly stretched in time. The hair cover of animals living in water has significantly less sharp seasonal differences and remains relatively thick even in summer. This is due to the weaker temperature fluctuations and the increased thermal conductivity of the water, which requires good protection from cooling throughout the year.

Some mammals (white hare, ermine, weasel, arctic fox) turn white for the winter. The whitewashing time generally coincides with the average multiyear dates for the establishment of snow cover. But in some years this coincidence does not work, and the premature whitening of hares sometimes turns out to be fatal for them. The white color has a masking (cryptic) value. The assumptions about its role in thermoregulation have not been confirmed by specially designed experiments.

Summer coloration sometimes also has a protective meaning, well disguising the hidden animal; for example, the spotted pattern of young roe deer and deer, striped young wild boars, sandy coloration of many desert rodents, etc. In a number of cases, the nature of the coloration is apparently explained by the influence of temperature, air humidity and other environmental factors. It is no coincidence that many fur-bearing animals of Eastern Siberia and Yakutia, where the climate is sharply continental, have not only the fluffiest, but also the darkest fur (sable, squirrel).

The hairline is closely related to the skin. It is composed of two main layers: the superficial epidermis and the deeper corium, consisting mainly of fibrous connective tissue. The cells of the epidermis, as they approach its surface, become more and more horny, die off and gradually slough off, being replaced by new cells coming from a deeper layer, which is called the malpighian. In the latter, the surface layer of the corium protrudes in the form of papillae. In these papillae, the smallest blood capillaries and tactile bodies develop. Deeper in the skin are blood vessels, nerves and fat. The skin of mammals is very abundant in glands - tubular and alveolar. The former include mainly sweat glands, the latter - sebaceous. As mentioned above, the mammary glands are a kind of modification of the tubular glands.

Hair is a derivative of the epidermis, although its roots are located in deep layers of connective tissue. Derivatives of the epidermis also include such horny formations as claws, hooves, scales (for example, armor of armadillos and lizards; small scales on the tail of a beaver, desman, etc.), partly horns of bovids, in which a horny substance in the form of a sheath covers the bone shaft. Claws, horns and others, like hair, experience age-related and seasonal changes.

Skeleton. The spine consists of five sections: cervical, thoracic, lumbar, sacral and caudal. The vertebrae have flat articular surfaces characteristic of mammals and are separated by round cartilaginous discs - menisci.

Fig. 3. Mammalian skeleton

1 - skull; 2 - lower jaw; 3 - cervical vertebrae; 4 - thoracic vertebrae; 5 - lumbar vertebrae; 6 - sacrum; 7 - caudal vertebrae; 8 - ribs; 9 - sternum; 10 - scapula; 11 - humerus; 12 - ulna; 13 - radius bone; 14 - wrist bones; 15 - bones of the metacarpus; 16 - phalanges of the fingers of the forelimb; 17 - pelvis; 18 - femur; 19 - tibia; 20 - fibula; 21 - bones are tarsus; 22 - metatarsal bones; 23 - phalanges of the toes of the hind limb; 24 - kneecap

The skull is divided into axial, consisting of bones surrounding the brain, and visceral (facial), which includes bones surrounding the mouth opening - the palate, bones of the upper and lower jaws. The shoulder girdle is represented only by the scapula and collarbone, and mammals do not have a crow bone (coracoid). In fast runners, the collarbone (ungulates) usually disappears as well. The pelvic region consists of a pair of nameless bones, each of which is formed by the fusion of the ilium, ischium, and pubic bones. The paired limb skeleton has three typical sections. In the forelimbs, this is the shoulder, forearm and hand, and in the hind limbs, the thigh, lower leg and foot. In mammals, a rounded tendon bone appears on the hind limbs at the knee joint - the patella.

The muscular system. This system in animals reaches exceptional development and complexity. They have several hundred individual striated muscles. A feature of the muscular system of mammals is the presence of a diaphragm and the appearance of subcutaneous muscles. The diaphragm is a domed muscular septum that separates the thoracic region from the abdominal region. In the center, it is perforated by the esophagus. The diaphragm takes part in the acts of respiration and excrement of animals. The subcutaneous musculature is a continuous subcutaneous layer. With its help, animals can move skin areas. The same muscles take part in the formation of the lips and cheeks. In monkeys, it almost disappeared and remained only on the face. There she received an unusually strong development - this is the so-called facial muscles.

Nervous system. The brain of the animal has a powerfully developed hemispheres of the forebrain and cerebellum. They cover all other parts of the brain from above. The forebrain consists of the cerebral hemispheres covered with the gray medulla - the cerebral cortex. The olfactory lobes move forward from the hemispheres. A wide jumper of white nerve fibers is located between the hemispheres.

The diencephalon has a funnel and a chiasm of the optic nerves, like other classes of vertebrates. The pituitary gland is attached to the funnel of the diencephalon, while the pineal gland is located above the cerebellum on a long stem. The midbrain is very small in size, in addition to the longitudinal groove, it also has a transverse one, which is characteristic only of mammals. The cerebellum consists of an unpaired part - a worm and two lateral ones, which are very large and are usually designated as cerebellar hemispheres. The medulla oblongata has a feature that is also characteristic only of mammals. On the sides of this brain, bundles of nerve fibers are isolated, going to the cerebellum. They are called the hind legs of the cerebellum. The medulla oblongata passes into the spinal cord.

Sense organs. They are very developed in mammals, and, in accordance with the ecological specialization of a particular group, the leading role is played by smell, sight, hearing, or touch. The hearing organs in animals are especially well developed. They have bony auditory drums and large, movable outer ears.

Digestive organs. The oral cavity is limited in animals by the lips. The lips take part in grasping and holding prey. The oral cavity is bounded from above by a hard bony palate. Due to this, the choanas (internal nostrils) are pushed back towards the pharynx. This allows the animals to breathe while the food is in the mouth. The sides of the oral cavity are bounded by soft, muscular cheeks, and at the bottom of the mouth is a large muscular tongue. Its functions are to perceive taste and push food while chewing under the teeth and down the throat while swallowing. The ducts of the salivary glands open into the mouth (4 paired glands - parotid, infraorbital, submandibular and sublingual). The teeth do not adhere to the surface of the bone, as in the previous classes, but sit in independent cells. The teeth are differentiated into incisors, canines and molars. The tooth itself consists of parts such as a crown with a working surface, the body of the tooth and its root. The pharynx of animals is short, the windpipe and choanas open into it. Thus, in mammals, the pharynx is the intersection of two pathways - food and respiratory. The esophagus is a simple, highly expandable muscular tube. After passing through the diaphragm, it connects to the stomach. The stomach has the appearance of a large, horseshoe-shaped, curved sac that lies across the body. A fat-filled peritoneum hangs from the stomach, which covers all internal organs with an apron. The liver is located under the diaphragm, its flows open into the duodenum, in the loop of which the pancreas lies. Most mammals have a gallbladder. The intestines can be of different lengths, depending on the composition of the feed. The herbivorous rabbit has a very long intestine - 15-16 times longer than the body. Its divisions are the small, large and rectum. At the beginning of the large intestine, mammals have an unpaired cecum - the cecum. The intestine opens outward with an independent anal opening.

Respiratory system. The larynx, as usual for mammals, has cricoid cartilage, in front of which is a large thyroid cartilage. The mammalian larynx is complex. On the inside of the larynx, the vocal cords are stretched. These are paired elastic folds of the mucous membrane, stretched in the laryngeal cavity and limiting the glottis. The lungs are a pair of spongy bodies hanging freely into the chest cavity. Their internal structure is characterized by great complexity. The trachea near the lungs is divided into two bronchi. The bronchi, entering the lungs, are divided into secondary bronchi, which in turn are divided into bronchi of the third and fourth order. They end with bronchioles. The ends of the bronchioles are swollen and braided with blood vessels. These are the so-called alveoli, where gas exchange takes place.

Circulatory system. The heart of animals, like that of birds, is four-chambered, and the left ventricle drives blood through a large circle of blood circulation and, like in birds, has much thicker walls than the right one. A large vessel departs from the left ventricle - the aorta, which begins the systemic circulation. All organs of the body are supplied with arterial blood, and venous blood is collected through the vein system. The largest of them - the posterior and two anterior vena cava - flow into the right atrium. From the right atrium, blood enters the right ventricle, from here begins a small circle of blood circulation, or, as it is also called, pulmonary. Venous blood is expelled from the right ventricle into the large pulmonary artery. This artery divides into right and left, leading to the lungs. From each lung, blood is collected in the pulmonary vein (blood in it is arterial), both veins merge and flow into the left atrium. Further, from the left atrium, blood is poured into the left ventricle and again goes through a large circle of blood circulation.

Organs, secretions. In mammals, this is a pair of bean-shaped buds located in the lumbar region. From the inner concave side of each kidney, there is a ureter (thin tube) that flows directly into the bladder. The bladder opens into the urethra.

Genital organs. In mammals, these are paired testes (in males) or paired ovaries (in females). Testes have a characteristic oval shape. The appendages of the testes are adjacent to them. Paired vas deferens open at the beginning of the urethra. The end parts of the vas deferens are expanded into seminal vesicles. The paired ovaries of the female have an oval-flattened shape. An oviduct is located near each ovary. At one end, the oviduct opens into the body cavity, and with the opposite end, without a visible border, it passes into the uterus. The uterus in animals is two-horned, the right and left horns of the uterus open independently into the vagina. It is unpaired. With its rear end, it gradually passes into the urethra and the bladder opens into it. Outside, the vagina opens with the urogenital opening.

The development of the embryo. Egg cells develop in the ovary, then mature cells, upon exiting the ovary into the body cavity, are trapped there by the funnel of the oviduct. Due to the ciliated movements of the cilia of the tube (oviduct), the egg moves along it, and if the female is fertilized, then in the tube (usually in the first third of it), the egg merges with the sperm. The fertilized egg continues to slowly descend into the uterus and at the same time begins to break up (division of the egg into many cells). Having reached the uterus, the egg, which by that time had turned into a dense multicellular ball, is introduced into the wall. There, nutrients begin to flow to it. Pretty soon, a placenta forms around the embedded embryo. This is the shell of the fetus, very characteristic of mammals. The placenta is a spongy organ rich in blood vessels, in which the child and maternal parts are distinguished. The nursery consists of the villi of the embryonic membrane, and the mother's - of the wall of the uterus. During childbirth, the muscular layer of the uterus is greatly reduced and the children's placenta (chorion), by that time connected very slightly to the mucous membrane of the uterus, opens and goes out together with the newborn in the form of a child's place.

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