MORPHOLOGY, ULTRASTRUCTURE AND FUNCTION OF THE PALMEN BODY AND CONTACT MALLET

摘要

The Palmen body and the similar contact mallet have been incorrectly and incompletely described since their discovery by Palmen in 1877. The Palmen body of a mature mayfly is made of multiple Palmen body units stacked like unique nested boxes, where the latest formed unit (larger than the previous one of the previous instar) covers and overlaps the previous unit. This overlap gives the illusion of rings, where none really exist. Counts of "rings" are then useful in instar determination. Two-dimensionally, Palmen body formation and structure/ultrastructure are very similar to tracheae, while in three dimensions Palmen cuticle differs greatly. Each unit has multiple uniformly distributed projections that span the interunit space. Each projection is hollow and open on the outer side, as if poking a finger through dough from the outside in. These projections make counting "rings" of whole Palmen bodies difficult or impossible with compound light microscopy because they scatter the light used to view the rings. Palmen bodies appear to lack the inner epicuticle and granular layer that the tracheal cuticle possess. Palmen bodies and contact mallets are not innervated and probably have no real function, as evident from body and head tracheal comparisons with Odonata.