The most diverse class is insects, the external structure and internal organs of which are well researched. From other types of arthropods, insects are distinguished by dividing the body into three sections: the head, chest and abdomen. As a rule, the external structure of insects is studied using the example of a May beetle or grasshopper.
Insects lack an internal skeleton. Its role is performed by a solid, dense surface of the body - the cuticle. It performs a protective and supporting function, creates a kind of skeleton.
The exoskeleton is attached to the muscles, and its surface is a barrier separating the body cavities from the environment. The cuticle can be hard or soft, turning into a shell. In some cases, the cuticle on the head and chest is stiff, on the abdomen - soft.
The larvae have a flexible, stretching cuticle because of the rapid growth. They can shed a few times, dropping the old shell. Some parts of the body of the insect can be additionally protected by plates and shields.
The outer structure of insects will begin to be studied from the head. At first glance, it seems that the head is a single whole, but evolutionally it was formed by the fusion of 5 segments.
On the head there are antennae and three pairs of mouth limbs. They are divided into upper, lower jaws and lower lip (a pair of fused jaws). Oral extremities in different insects differ and are divided into several species depending on the type of food:
- Gnawing, for solid food, for example, as in predatory bugs;
- Piercing-sucking, if you need to pierce the food substrate, there are mosquitoes, bedbugs, cicadas;
- Tubular-sucking, if piercing is not required, as in butterflies;
- Gnawing and licking for liquid food in bees, wasps;
- Muscovite for feeding liquid and solid food in flies.
On the sides of the head are complex eyes, and between them from one to three simple eyes. Before the eyes - antennae, which are also divided into several types.
We continue to study the external structure of insects. Breasts of insects can be divided into three large segments, in which even smaller ones are distinguished. At the bottom of the chest are legs. The trochanter and the basin ensure mobility of the limb. The thigh is the largest and strongest part of the leg, equipped with powerful musculature.
Then follow the knee and shin, which is equipped with spurs and thorns. The paw itself is divided into several small segments, at the apex there are claws and suckers. Features of the external structure of insects depend on the species. Legs can also have specialization and are divided into types.
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 they have a similar structure. Most often the wings are two pairs, they are outgrowths located on the back. They consist of the finest plates, reinforced with rigid veins.
The external structure of the body of an insect depends on the way of life. In connection with the performance of various functions, the wings have undergone a number of changes. In Diptera, the hindwings were transformed into hind wings, and in the wingwing - the anterior ones. In beetles, the front wings evolved into the elytra, the mantis and cockroaches became leathery, etc. For some insect species, the wings are absent in the same sex or completely in all individuals.
We finish studying the external structure of insects with the belly. This part consists of a set of identical segments, usually of ten. On the 8th and 9th segments, the sexual appendages and openings are located. In the abdomen are located almost all internal organs.
There are no extremities on the abdomen, but larvae may have false legs there. In the posterior segments are located the copulatory organ in males, the ovipositor in females and the anal opening. Table "External structure of an insect" will help to better understand the features of the structure of these representatives of the animal world.
Respiratory and circulatory system
The external and internal structure of insects depends on the way of life that they lead. The respiratory system consists of trachea, they permeate the entire body. They are opened by spiracles, regulating the intake of air. In insects breathing air, the respiratory system is open. In water it is closed, spiracles absent. Larvae may have gills.
Air enters through the holes of the spiracles and penetrates the trachea, entangling the internal organs. Trachea end in branched tracheal cells and tracheoles, the tips of which penetrate into the cells.
Hemolymph does not participate in gas exchange, this role is performed by the trachea. Hemolymph is pumped by the heart located on the back. It looks like a muscular tube.
Hemolymph enters this tube through the hole 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, supplying them with the necessary substances.
Digestive and excretory systems
Let us continue studying the external structure of insects and their internal organs. The digestive system begins with the oral cavity, where the ducts of the salivary glands enter. Saliva contains enzymes for the breakdown of food. Then follows the esophagus, goiter, stomach. The intestine is divided into three sections by means of two valves and ends with an anal opening. In some species the digestive system in the adult state is not developed. For example, the pods do not have jaws, the intestines are reduced. They live for several days and do not eat.
The organs of insect secretion are represented by malpighian vessels and the hindgut. Malpighian vessels are the ducts located between the middle and the back of the intestine. The products of vital activity are filtered out by the walls of the vessels and are discharged into the hindgut.
Endocrine and reproductive systems
The organs of the endocrine system secrete hormones in the hemolymph that regulate such physiological processes as metabolism, reproduction, behavior, etc.
Insects are dioecious animals. The reproductive system of males is represented by two testes, the vas deferens and the ejaculatory duct. The reproductive system of females is represented by the ovaries and oviduct.
During mating, the seminal fluid enters the female spermatheca and is stored there. Mating can last up to several days, most species immediately part. During the laying, eggs are lubricated with sperm and fertilized. All the strengths of the organism are spent on reproduction, therefore females either actively feed on or die.
Nervous system and sense organs
The nervous system of insects has a complex structure. It consists of neurons. In the nerve cell, you can distinguish the body, dendrites and axon. Through the dendrites, the cells receive signals, and through the axon exchange information.
The central nervous system is represented by the suprapharyngeal nerve node and the ventral 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 to organs and tissues. The vegetative system consists of separate ganglia, which regulate the management of organs.
Through the sense organs , the nervous system receives information.
Vision is represented by faceted eyes, several simple eyes or larval eyes.
Hearing organs can be located on different parts of the body. They are presented by vibroreceptors in the legs of terrestrial insects, which feel the vibration of the substrate. Sounds through water and air are perceived by phonoreceptors, and Diptera are heard with johnstones. The most complex organs of hearing are tympanal organs.
The organs of taste are located on the legs, abdomen and in the oral cavity. The organs of touch are located throughout the body. Organs of smell - on antennae.
The internal and external structure of insects can be very different in different species. It depends on the lifestyle and type of nutrition. The table "External structure of an insect", which is placed in this article above, will help to systematize the received knowledge.