Can You Describe The Physiology Of The Earthworm?


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Steve Theunissen Profile
The common earthworm measures about ten inches (25 centimeters) in length. It consists of about 120 (or up to 150) cylindrical segments. If a few of these segments are lost, perhaps because of being picked off by a bird, they will regenerate. However, such regeneration has limitations. Therefore, cutting an earthworm in half will not result in two separate worms. Each segment, with the exception of the first and the last, is equipped with eight bristles known as "setae." By means of these bristles the earthworm can get a good hold on the soil through which it crawls. This creature's longitudinal muscles enable it to contract or to stretch itself. With the circular muscles, it can make its tubelike body shrink or expand. Five pairs of hearts form part of the earthworm's circulatory system.

Unlike many other creatures, earthworms have no eyes, no ears, and no lungs or gills. The skin is supplied with light-sensitive cells. So when exposed to bright light, the earthworm will quickly withdraw into the darkness of its underground realm. Endowed with a keen sense of feeling, it can detect the slightest vibrations, including the movement of a mouse or a bird. The creature does all its breathing through the skin.

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