Ultrastructural observation showed that a great number of long elliptical extrusomes were distributed beneath the pellicle on the dorsal and ventral sides of a hypotrichous ciliate , Oxytricha granulifera.The mature extrusomes were filled with different electron dense fibrous materials at their posterior parts , and had hollow cavities at their anterior parts .The anterior end of the mature extruso-mes was close to the pellicle, and distributed in longitudinal, diagonal or arc rows.During ejection, the anterior membrane of extruso-mes fused with the plasma membrane .After extrusion , the extruded contents often remained in the surface of the cells .Considered that the extruded contents of extrusomes of O.granulifera always adhere to the surfaces of the cells and its morphology has no obvious differ -ence from the resting extrusomes , it can be supposed that during ejection , the contents may be slowly excreted toward outside through the pellicle.Therefore, the extrusomes of O.granulifera might be a kind of excretion extrusomes .Besides, the extrusomes of O.gran-ulifera can be stained by alcian blue 8GS which can rapidly stain mucin , carboxyl and sulphate-containing mucosubstances , therefore, the extrusomes of O.granulifera may contain some mucosubstances .Under the stimulus of methyl green-pyronin, the extrusomes of O. granulifera were numerously discharged , and the extruded contents of extrusomes got together to form a "capsule"which packed the ciliate in it, thus, it might be a defensive response to harmful conditions .%超微结构观察显示，腹毛类纤毛虫颗粒尖毛虫（ Oxytricha granulifera）的整个背腹皮层表膜下分布大量的长椭圆形射出胞器。胞器发育成熟后，在泡后部充满不同电子密度的纤维物质，在泡前端形成凹陷小窝。成熟射出胞器前端紧贴表膜，以纵向、斜向或弧形的列位于表膜下。胞器射出时，前端的膜与细胞质膜融合，射出内容物后，射出物常留在细胞表面。联系胞器射出后射出物常黏附在细胞表面，且其形态与成熟射出胞器无明显差异的现象，推测胞器射出时射出物可能经历了通过表膜向细胞外缓慢逸出的过程，因此，该射出胞器可能是一类分泌型射出胞器。此外，颗粒尖毛虫的射出胞器可被阿尔新蓝溶液标记，由于该溶液可以快速地标记粘蛋白（ mucin）及羧基化或硫酸化的粘液物质，因此认为，颗粒尖毛虫射出胞器可能含此类粘液物质；在甲基绿－派洛宁的刺激下，颗粒尖毛虫的射出胞器大量射出，射出物黏附聚集形成“壳”，将纤毛虫包裹在内，据此认为，这可能是细胞在不利环境条件下形成的一种防御机制。
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