Histological observations on the Saccus vasculosus in three species of
Elasmobrachii and 20 species of
Teleostei (9 marine, 11 freshwater fishes) were made.
1. In 20 species of the fishes except
Cyprinus auratus, Carassius auratus and
Lebistes reticulates, the Saccus vasculosus lies between the base of the brain and pituitary body and extends bilaterally on the surface of Lobi inferiores. In
Teleostei, the saccus is located posterior to the pituitary body, connected (
Paralichthys olivaceus, Anguilla japonica, Misgurunus anguillicaudatus, Astroconger myriaster and
Plecoglossus altivelis etc.) or unconnected with pituitary body (
Monacanthus cirrhifer, Platycephalus indicus, Inimicus japonicus and
Spheroides niphobles etc.). In some species, it remains undeveloped (
Parasilurus asotus) or defective (
Cyprinus carpio, Carassius auratus and
Lebistes reticulatus). Channa argus has no saccus and the basal surface of the third ventriculum is exposed on the surface of base of the brain with striking folds.
2. Epithelial cells of Saccus vasculosus consist of support cells (Stützzellen) and crown cells (Krönchenzellen). There are remarkable differeces in the size and shape of crown cell within the species. Support cells lie between crown cells and their nuclei are situated beneath the surface of the ventriculum. The cell has no protoplasmic processes to the ventricular surface and is regarded as a special glia cell. The processes run parallel to the surface of ventriculum forming a kind of mesh work of glia membrane, through which the processes of crown cell run.
3. In subepithelial tissues, there are fine capillaries and many sinusoidal vessels of different sizes; which extend through the thin basal membrane face of the epithelial cell. The connective tissue components filling the vascular space originate from the meninx, and include a lot of elastic fibers. Bundles of nerve fibers connecting the epithelial cell with the mesencephalon run through this stromal layer.
4. Various kinds of regulatory apparatus of circulation, that is, arteriovenous anastmoses, and arterial valves or many ‘Turbanorgane’ in
Dasibatis akajei, are attached to the vascular system around the Saccus vasculosus. These apparatus are regarded as regulators of the blood volume in the saccus.
5. There is no remarkable difference in the evolutional development of the Saccus vasculosus between the marine and freshwater fishes, even between
Anguilla japonica living in freshwater and that in brackish water, either macroscopically or microscopically.
6. Inside of the Saccus vasculosus of
Cyprinus carpio, there is found a kind of colloidal substance which reveals positive PAS reaction and is fast staining to chromehematoxylin. Inside of the sinusoidal vessels of
Parasilurus asotus and
Astroconger myriaster, is a substance that is fast staining to chrome hematoxylin and victoria blue. The crown cell contains no substance or granule, which shows any significant fat, polysaccharide and phosphatase reaction etc., and reveals no reaction to adrenalin, pilocarpin and acetylcholine etc.
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