The most diverse class is insects, the external structure and internal organs of which are well studied. Insects differ from other types of arthropods by dividing the body into three sections: head, chest, and abdomen. As a rule, the external structure of insects is studied on the example of a May beetle or grasshopper.
Exoskeleton
Insects lack an internal skeleton. Its role is played by a solid dense surface of the body - the cuticle. It performs a protective and supporting function, creates a kind of frame.
Muscles are attached to the exoskeleton, and its surface is a barrier separating body cavities from the environment. The cuticle can be hard or soft, turning into a shell. In some cases, the cuticle is stiff on the head and chest, and soft on the abdomen.
Larvae due to their rapid growth have a flexible, stretching cuticle. They can molt several times, dropping the old shell. Some parts of the body of the insect can be further protected by plates and shields.
Head
We begin to study the external structure of insects from the head. At first glance, it seems that the head is a single whole, but evolutionarily it was formed by the merger of 5 segments.
On the head are antennae and three pairs of oral limbs. They are divided into upper, lower jaws and lower lip (a pair of fused jaws). The mouth limbs of different insects differ and are divided into several types depending on the type of food:
- gnawing, for solid food, for example, as in predatory beetles;
- stinging-sucking, if you need to pierce the food substrate, mosquitoes, bugs, cicadas have it;
- tubular sucking, if piercing is not required, like butterflies;
- gnawing-licking for liquid food in bees, wasps;
- muskoid for feeding liquid and solid foods in flies.
Complex eyes are located on the sides of the head, and between one and three simple eyes are located between them. Before the eyes - antennae, which are also divided into several types.
Chest
We continue to study the external structure of insects. The chest of insects can be divided into three large segments, in which even smaller ones stand out. The legs are attached at the bottom of the chest. A swivel and a basin provide mobility of the limb. The thigh is the largest and strongest part of the leg, equipped with powerful muscles.
This is followed by a knee and lower leg, which is equipped with spurs and spikes. The foot itself is divided into several small segments, at the top there are claws and suction cups. Features of the external structure of insects depend on the species. Legs can also have specialization and are divided into types.
Wings
The external structure of insects is interesting to study due to the diversity of species. The wings of butterflies and mosquitoes differ in appearance, but have a similar structure. Most often, the wings are two pairs, they are outgrowths located on the back. They consist of the thinnest plates reinforced with rigid veins.
The external structure of the body of the insect depends on the lifestyle. In connection with the performance of various functions, the wings have undergone a number of changes. In the Diptera, the hind wings transformed into a ground beetle, and in the fan-winged wing, the front wings. In beetles, the front wings evolved into elytra, in mantis and cockroaches they became leathery, etc. In some species of insects, wings are absent in representatives of the same sex or completely in all individuals.
Abdomen
We finish studying the external structure of insects by the abdomen. This part consists of many identical segments, usually ten. On the 8th and 9th segments there are genital appendages and holes. Almost all internal organs are located in the abdomen.
There are no extremities on the abdomen, but the larvae may have false legs. In the posterior segments are the copulative organ in males, the ovipositor in females and the anus. The table “External structure of the insect” will help to better understand the structural features of these representatives of the animal world.
Respiratory and circulatory system
The external and internal structure of insects depends on the lifestyle that they lead. The respiratory system consists of tracheas, they permeate the entire body. They open with spiracles that regulate the flow of air. In insects that breathe air, the respiratory system is open. In water, it is closed, spiracles are absent. Larvae may have gills.
Air enters through the openings of the spiracles and enters the trachea, entangling internal organs. Tracheas end in branched tracheal cells and tracheols, the tips of which penetrate into the cells.
Hemolymph is not involved in gas exchange; the trachea plays this role. Hemolymph is pumped using a heart located on the back. The organ looks like a muscular tube.
Hemolymph enters this tube through an opening and moves in the direction from the abdomen to the head. At the other end, the hemolymph freely enters directly into the body cavity and flows around the internal organs, nourishing them with the necessary substances.
Digestive and excretory systems
We continue the study of the external structure of insects and their internal organs. The digestive system begins with the oral cavity, into which the ducts of the salivary glands flow. Saliva contains enzymes to break down food. This is followed by the esophagus, goiter, stomach. The intestine is divided into three departments using two valves and ends with the anus. In some species, the digestive system in adulthood is not developed. For example, mayflies have no jaws, the intestines are reduced. They live for several days and do not eat.
The excretory organs in insects are represented by malpigian vessels and the hind gut. Malpighian vessels are tubes located between the middle and hind gut. Vital products are filtered by the walls of blood vessels and excreted into the hind gut.
Endocrine and reproductive systems
The organs of the endocrine system secrete hormones into hemolymph that regulate physiological processes such as metabolism, reproduction, behavior, etc.
Insects are dioecious animals. The reproductive system of males is represented by two testes, vas deferens and the ejaculatory canal. The female reproductive system is represented by the ovaries and oviduct.
During mating, the seminal fluid enters the female sperm and is stored there. Mating can last up to several days, most species immediately part. During the laying, the eggs are smeared with sperm and fertilized. All body forces are spent on reproduction, so females either actively eat or die.
Nervous system and sensory organs
The nervous system of insects has a complex structure. It consists of neurons. In the nerve cell, the body, dendrites and axon can be distinguished. Through dendrites, cells receive signals, and through the axon exchange information.
The central nervous system is represented by the supraglottic nerve node and the abdominal chain, which consist of ganglia. These organs control the activity of all organs and tissues. The peripheral system is the motor and sensory nerves that connect the central nervous system with organs and tissues. The autonomic system consists of individual ganglia that regulate the management of organs.
Through the senses, information enters the nervous system.
Vision is represented by faceted eyes, a few simple eyes or larval eyes.
Hearing organs can be located on various parts of the body. They are represented by vibration receptors in the legs of terrestrial insects that sense the vibration of the substrate. Sounds through water and air are perceived by phonoreceptors, and dipterans hear with the help of Johnston organs. The most complex organs of hearing are the tympanic organs.
The taste organs are located on the legs, abdomen and in the oral cavity. The organs of touch are located throughout the body. The organs of smell are on the antennae.
The internal and external structure of insects can vary greatly between species. It depends on the lifestyle and type of food. The table “External structure of the insect”, which is posted in this article above, will help to systematize the knowledge gained.