Der Ort der Osmoregulatorischen Salzaufnahme bei den Schwimmkäfern Dytiscus marginalis und Acilius sulcatus

Abstract Short-term experiments with hypo-osmotic, radioactive sodium chloride solutions revealed that larval Dytiscus marginalis L. and Acilius sulcatus L. (Coleoptera, Dytiscidae) take up these ions into the hemolymph almost exclusively through the intestine by drinking. Out of 20 Acilius larvae whose mouth had been occluded, 7 were also able to ingest the external solution through the anus. The results of fine-structural investigations lead to the conclusion that the ileum, which is lined by a highly differentiated transporting epithelium throughout its entire length, is the main site of ion absorption. Both the rectum, which lacks the rectal papillae, and the rectal caecum possess a thin epithelium showing no structural indications of any substantial active transport function.