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.
Animals with open circulations (ex. insects): Circulatory fluid escapes the vasculature and bathes all. the cells of the body = hemolymph. No distinction. between blood and interstitial fluid. Animals with closed circulation (ex. vertebrates): Blood is confined to vessels and is not in direct contact. with tissue cells. Interstitial fluid bathes cells, and is. served by plasma of the circulatory system for. transport.