The cercaria described here was found on 21 April 1936, in twelve out of sixteen specimens of Nucula nucleus (L.) from Cawsand Bay, Plymouth Sound. The parasite was found by Dr Marie V. Lebour, who kindly gave me the infested molluscs for examination. I have thought it advisable to publish these notes, incomplete as they are, as it may not be possible for me to obtain further specimens of infested Nucula for some time to come.The trematode was found to parasitize the digestive gland and gonad. The cercariae develop in irregularly shaped parthenitae which each contain from, two to ten larvae in various stages of development. The parthenitae measure 0.9–2.0 mm. in length.The cercaria is very large and has a long, forked tail (Fig. 1). The measurements on the left of Table I were made with an ocular micrometer when the living cercariae were slightly flattened under the pressure of a cover-slip.The body is elongate in outline, with a slight constriction just behind the oral sucker, and reaches its greatest diameter opposite the ventral sucker. The pre-acetabular region of the body is highly muscular and capable of much. extension and contraction. Near the posterior border of the oral sucker there are two blunt processes, ventro-lateral in position. In section, the body is somewhat cylindrical, and consequently it is almost impossible to obtain true measurements from living cercariae because different individuals could not be subjected to the same pressure under a cover-glass. The measurements given on the right of Table I are of mature cercariae fixed in Bouin's fluid without pressure, and supplement those of living cercariae.

中文翻译：

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来自 Nucula Nucleus (L.) 的单尾蚴属尾蚴

此处描述的尾蚴于 1936 年 4 月 21 日在 16 个标本中的 12 个中发现核(L.) 来自普利茅斯湾的考沙湾。寄生虫是由 Marie V. Lebour 博士发现的，他好心地将受感染的软体动物交给我检查。我认为发布这些笔记是明智的，尽管它们并不完整，因为我可能无法获得更多的受感染样本纽库拉一段时间以后。发现吸虫寄生在消化腺和性腺上。尾蚴发育成不规则形状的单翅目，每只单胞胎都含有 2 到 10 只处于不同发育阶段的幼虫。单足长为 0.9-2.0 毫米。尾蚴非常大，尾巴很长，呈叉状（图 1）。表 I 左侧的测量是在活体尾蚴在盖玻片的压力下略微变平时用目镜测微计进行的。身体轮廓细长，在口腔吸盘后面有轻微收缩，并到达其腹吸盘对面的最大直径。身体的前髋臼区域肌肉发达，可以做很多事情。伸展和收缩。靠近口吸盘的后缘有两个钝突，位于腹外侧。在剖面上，身体有点圆柱形，因此几乎不可能从活尾蚴获得真实的测量结果，因为不同的个体不能在盖玻片下承受相同的压力。表 I 右侧给出的测量值是在无压力下固定在 Bouin 液中的成熟尾蚴，并补充了活体尾蚴的测量值。