A combination of factors is likely causing the decline of blue spruce trees throughout Michigan. Posted on March 7, 2011 by Dennis Fulbright, Michigan State University Extension, Department of Plant Pathology, and Jill OâDonnell, Michigan State University Extension.
Flatworms lack a respiratory or circulatory system; these functions take place by absorption through the body wall. Nonparasitic forms have a simple, incomplete gut; even this is lacking in many parasitic species. Movement in some flatworms is controlled by longitudinal, circular, and oblique layers of muscle.
An earthworm has a closed circulatory system that uses vessels to send blood through its body. There are five aortic arches throughout his body that serve as pumps. The dorsal vessels take blood from the back of his body to the front, and the ventral vessels take blood the other direction, from front to back. Smaller capillaries help the blood absorb nutrients and oxygen or carbon dioxide and carry them to the proper areas of his body.