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.
Roundworms do not breathe in the sense that vertebrates, such as humans and other mammals, do. Instead, roundworms (also known as nematodes) obtain the oxygen their bodies need through diffusion, a process of gas exchange commonly used among flatworms and earthworms as well. Diffusion allows roundworms to provide oxygen to their cells without the use of complex organs, such as lungs. In terms of their anatomy, roundworms are simplistic. They lack skeletons, blood vessels, lungs, even a brain. They do have a digestive system that is as long as their bodies.