A contribution to the functional morphology of the midgut gland in phalangiid harvestmen Gyas annulatus and Gyas titanus during their life cycle.

The structure of the midgut gland and its changes in different seasons have been examined in the harvestmen Gyas annulatus and Gyas titanus (Arachnida: Opiliones: Phalangiidae). In both species, in the epithelium of the midgut gland two different types of cells are present: secretory and digestive ones. The secretory cells are characterized by plentiful rER and secretory granula. The digestive cells are characterized by an apical system of tubules. Both cells are connected by prominent specialized junctions. If a secretory cell is in contact with a digestive cell, rER cisterna are in close vicinity and parallel to these junctions. As found light- and electron microscopically and also histochemically, glycogen and lipids are stored in both cells. In both species, glycogen was seen to be used as energy compound during overwintering. At the end of their life, the digestive cells develop into excretory ones, containing metabolic wastes.