Morphology and structural organization of Gene's organ in Dermacentor reticulatus (Acari : Ixodidae)

Scanning and transmission electron microscopical investigations revealed th at Gene's organ in unfed and ovipositing females of Dermacentor reticulatus is formed as a double-sac-structure consisting of an outer epithelial and an inner cuticular sac. In ovipositing ticks the latter emerges through the camerostomal aperture to the exterior. Gene's organ in unfed ticks consist s of a corpus, two posterior horns and a pair of undeveloped glands at each side, which differentiate in ovipositing ticks to compound, branched tubul ar glands with a main efferent duct for each gland opening into the lumen b etween the epithelial and the cuticular sac. Gene's organ of egg-laying fem ales corresponds basically in morphology and structural organization to tha t of unfed ticks. Compared with unfed ticks, however, in ovipositing ticks the corpus and horns are longer and broader, the glands are fully developed and the cuticular sac is evertable. The epithelial sac as the outermost pa rt of Gene's organ is continuous with the hypodermis of the basis capituli and the scutum, arises at the camerostomal aperture, forms the corpus and t he two blind-ending horns, passes into the epithelium of the main excretory ducts of the glands and envelops the cuticular sac. The cuticular sac pass es into the cuticle of the basis capituli and the scutum, arises at the cam erostomal aperture, is folded, expands into the horn tips and consists inwa rds of a smooth epicuticula and outwards of a fibrous endocuticula. Muscles originating from the scutum pass caudomedially through the epithelial sac and are inserted into the cuticular sac. The entire surface of the maximall y everted cuticular sac is covered with an amorphous mass. In cleaned sampl es, ledge-like structures appear on the lateral surface. These ledges turn into balloon-like structures which extend over the medial and dorsal surfac e. The entire surface including the balloon-like structures and the ledges are provided with numerous cribrate pits.