目的 利用扫描电子显微镜和透射电子显微镜对华支睾吸虫囊蚴脱囊的超微结构进行观察和分析。 方法 取华支睾吸虫阳性麦穗鱼，去除头、鱼鳞和内脏，称重后绞碎，按1 g∶10 ml比例加入人工消化液（成分为0.6 g胃蛋白酶，100 ml生理盐水，1 ml浓盐酸），于37 ℃消化过夜后反复过滤，体视显微镜下分离成熟囊蚴。加入0.025%胰蛋白酶溶液（pH = 7.4），37 ℃孵育约3 min，将脱囊后尾蚴、未完全脱出后尾蚴、外形较完整囊蚴及脱下空囊分开收集，使用3%戊二醛与1%四氧化锇固定制样。样品使用50%、70%、80%、90%、100%乙醇逐级浸泡脱水（每级10 min，100%乙醇脱水重复3次），100%六甲基二硅烷浸泡3次（每次10 min），干燥后镀膜喷金，使用扫描电子显微镜观察样品；按50%、70%、90%乙醇、1∶1混合液（90%乙醇∶90%丙酮）、90%、100%丙酮逐级脱水（每级10 min，100%丙酮脱水重复3次），依次于丙酮与包埋剂（环氧树脂618）1∶1、1∶3混合液与全包埋剂中浸泡后聚合处理，修块、切片、醋酸铀-柠檬酸铅双重染色，使用透射电子显微镜观察样品。 结果 扫描电镜下可见囊蚴外观出现了局部膨胀或凹陷、褶皱及塌陷、囊壁内外层分离；脱囊形成的线状裂口长、边缘平整，未能脱出的后尾蚴被软塌的囊壁包裹，其上皮棘刺穿囊壁；脱囊后尾蚴背、腹面遍布体棘，腹吸盘明显大于口吸盘，口、腹吸盘内壁结构不同；排泄囊内填满大小不一圆球形排泄颗粒。透射电镜下显示，脱囊后尾蚴体壁为合胞体结构，由外向内可见皮层外质膜下为电子致密的颗粒状基质，基质向表面形成突起，基质内含许多分泌颗粒及大小不等囊泡；皮棘根部从基质膜发出，穿过基质从皮层表面穿出；基层厚度差异较大，内含多个高电子密度分泌小体；外环肌和内纵肌发达，深入到细胞层，经胞质管运送的物质在远端形成囊泡；皮层细胞间物质发达，充满杂乱分布的管状、大小不等的囊泡结构及线粒体。 结论 囊蚴凭借发达的肌肉组织剧烈运动，在脱囊中起积极作用；皮棘有助于后尾蚴尽快摆脱软化囊壁的包裹；囊内后尾蚴可能借助运动触碰囊壁方式使皮层分泌物可直接作用于内壁，发挥化学性软化内壁作用来协助脱囊。

Objective To observe and analyze the ultrastructure of the metacercariae excystment of Clonorchis sinensis using scanning electron microscope and transmission electron microscope. Methods C. sinensis-positive fish pseudorasbora parva was subject to remove the head, scales and viscera, then weighed and minced. The minced fish was added with artificial digestive fluid (composed of 0.6 g of pepsin, 100 ml of normal saline, and 1 ml of concentrated hydrochloric acid) at a 1 g : 10 ml ratio and was digested overnight at 37 ℃, followed by repeated filtration. The mature metacercaria were separated under a stereomicroscope. Trypsin at a concentration of 0.025% (pH = 7.4) was added to the samples and incubated at 37 ℃ for approximately 3 min. The exysted cercaria, incompletely exysted metacercaria, metacercaria remain comparatively intact appearace, and existed empty sacs were collected separately and fixed with 3% glutaraldehyde supplemented and 1% osmium tetroxide. The fixed samples were dehydrated through a series of ethanol gradients (50%, 70%, 80%, 90%, and 100%, each for 10 min, with 100% ethanol repeated 3 times) and soaked in 100% hexamethyldisilazane 3 times (each for 10 min), dried, coated with gold, and observed using a scanning electron microscope. Gradient dehydration was performed using 50%, 70%, 90% ethanol, 1 : 1 mixture (90% ethanol with 90% acetone), 90% and 100% acetone (each stage was repeated 3 times for 10 min with 100% acetone dehydration). The samples were polymerized in the acetone with embedding reagent (epoxy resin 618) at 1 : 1 and 1 : 3 ratio or the whole embedding agent. The samples were trimmed, sliced and double-stained with uranyl citrate. The sample was observed by transmission electron microscope. Results The scanning electron microscopy revealed local swelling or shrinkage, folding and collapse, and separation of the inner from outer layers of the cyst wall; the linear crack formed during decapsulation was long and had smooth edges. The incompletely emerged metacestodes were wrapped in a soft collapsed cyst wall, with their epidermal spines piercing through the cyst wall; the decapsulated metacestodes were covered with body spines on the dorsal and ventral surfaces. The ventral sucker was significantly larger than the oral sucker, with different inner wall structures. The excretory bladder was filled with spherical excretory particles of various sizes. Transmission electron microscopy showed that the body wall of the decapsulated metacestodes was syncytial, with an electron-dense granular matrix underneath the cortical plasma membrane. The protrusions formed from the matrix towards the surface and numerous secretory granules and vesicles of various sizes within the matrix was seen. The spines originated from the basal membrane, penetrated through the matrix and emerged from the cortical surface. The basal layer had significant thickness variation and contained multiple high-electron-density secretory bodies; the outer circular muscle and inner longitudinal muscle were well-developed, extending into the cell layer with materials transported by cytoplasmic tubes forming vesicles at the distal end. The intercellular substance of the cortical cells was well-developed, filled with chaotically distributed tubular structures, vesicles of various sizes, and mitochondria. Conclusion The metacercariae exhibit vigorous movement via their well-developed muscle tissue, which plays an active role in exysting process. The dermal spines may assist the excysted metacercariae to rapidly escape from the softened wrapping cyst wall. The excysted metacercariae inside the cyst may stimulate the cyst wall via exercising to induce cortical sectetion, which could directly act on the cyst inwall, consequently, facilitate excystment by chemically softening the cyst inner wall.