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.
Next, trace the closed circulatory system of the earthworm. A closed circulatory system means there is a heart and blood vessels in the organism. First, in segment 7 to 11 are the five hearts of the worm. The hearts connect the dorsal blood vessel with the ventral blood vessel. Dorsal means to run along the back.