Unformatted text preview: rise to muscles and reproductive organs. Free living forms have muscles, a nerve cord, and digestive organs, but lack both the respiratory and circulatory systems common to the so-called "higher" animals (in other words like ourselves). Flatworms, as shown in Figure 18, have a branched gastrovascular cavity that is the site of extracellular digestion and which distributes nutrients throughout the body. Gas exchange occurs by diffusion through the skin. Platyhelminths have an excretory system that also functions as an osmotic-regulating system. Flatworms have a ladder-style nervous system composed of paired ganglia that form a brain connected via nerve cells to sensory cells in the body wall....
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- Fall '10
- Biology, Flatworms, Flatworm, bilateral symmetry, Trematoda