Image credits (top to bottom): Whole-mount image of a planarian fed red fluorescent dextrans, revealing the branched structure of the intestine (Dave Forsthoefel). Spermatogenesis in a planarian: confocal section through a testis lobe showing nuclei (gray-to-white) at different stages of development and phospho-Histone H3 staining (in red) (Tracy Chong). Schistosome-infected snail, labeled with a fluorescent lectin. Colors correspond to different depths in the tissue (Bo Wang).
Header: Schmidtea lugubris, from Steinmann and Bresslau, 1913.