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.
Most free-living flatworms have a gastrovascular-type digestive system (a mouth is present but no anus), while parasitic forms generally have no digestive system. Flatworms have a centralized nervous system consisting of pair of cerebral ganglia and longitudinal nerve cords connected to transverse nerves.n contrast to radiate and acoelomate phyla in which the space between the body wall and the digestive tract is filled with mesoglea or with solid mesenchymal parenchyma, the remaining bilateral animals covered in the Zoo Lab website have a body cavity in which internal organs are located.