The earthworm is a representative of the annelid type. Its long, elongated case consists of separate segments - rings, separated by ring constrictions, which explains the name of the species. Thanks to this structure, it can move freely both in dense soil and on the soil surface.
Instructions
Step 1
The body of the earthworm is elongated in length by 10-16 cm. It is rounded in cross-section, but longitudinally divided by annular constrictions into 100-180 segments. On them are elastic bristles, with which the worm clings to the unevenness of the soil during movement.
Step 2
During the day, worms are in the soil and make passages in it. They easily drill the soft one with the front end of the body: at first, it becomes thin, and the worm pushes it forward between the lumps of earth, then, thickening, the front end pushes the soil, and the worm pulls up the back of the body. In dense soil, worms can eat their own passages, passing it through the digestive tract. At night, they come to the surface of the soil and leave behind characteristic earthen piles.
Step 3
The skin of the earthworm is moist to the touch because it is covered in mucus, which makes it easier for the worm to move through the soil. The oxygen needed for breathing can also only penetrate through wet skin. Under it is the musculocutaneous sac - circular (transverse) muscles fused with the skin, under which lies a layer of longitudinal muscles. The former make the body of the animal long and thin, the latter thicken or shortened. The coordinated alternating work of these muscles ensures the movement of the worm.
Step 4
A fluid-filled body cavity can be seen under the skin-muscle sac. The internal organs of the animal are located in it. In contrast to roundworms, the body cavity of the rain worms is not continuous, but segmented, divided by transverse walls.
Step 5
At the front end of the body is the mouth. Rotting plant debris and fallen leaves, which the worm feeds on, it swallows along with the earth with the help of a muscular pharynx. Further, the digestive tract continues with the esophagus, goiter, stomach, intestine and anus. Through the latter, at the posterior end of the body, undigested food debris is thrown out along with the earth.
Step 6
The circulatory system of the earthworm has two main vessels: the dorsal and the abdominal. According to the first, the blood moves from back to front, along the abdominal - from front to back. In each segment, they are connected by annular vessels. Due to the contraction of the muscle walls, blood flows in several thick annular vessels.
Step 7
The main vessels branch into thinner ones, and those into the smallest capillaries. They receive nutrients from the intestines and oxygen from the skin. Such a circulatory system, in which blood moves only through the vessels and does not mix with the cavity fluid, is called closed.
