Acoelomates, pseudocoelomates, eucoelomates, ectoderm, mesoderm and endoderm. In a course surveying the various invertebrate phyla, these words are often used when comparisons are made. This set includes four slides selected to substantiate those comparisons. Cross sections of Hydra, Planaria (three regions), Ascaris, and the earthworm Lumbricus (two regions) are studied to determine which terms apply to each organism. In the process students will gain further appreciation for the remarkable complexity of form and function seen in the animal world.