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 also has the same type nervous system as a human, just like a pig. As for the circulatory system, a humanâs pumps blood to and from the body and lungs with the help of the heart, blood vessels, and arteries. A pig, however, has a heart, blood, blood vessels, lungs, and a circulatory mechanism.