Observations were made on details of tegument development of schistosomes grown in mouse, hamster, and rat hosts. In permissive hosts (mouse and hamster) the surface of the worm alters rapidly during early maturity and is characterized by fusing of a highly undulate surface network into smooth folds and spine-covered tubercles. In non-permissive hosts maturation of the tegument is both delayed and incomplete, and the tubercles are aspinous. Scanning views of the oral cavity and the gynegophoral canal, both sites of transitional tegumental organization, are also shown. The gynecophoral canal tegument seems to be a site of active lipid secretion.