The auther has made a careful and detailed studies of the characters of the cercaria of Schistosoma japonicum and summaried as follows: 1. It was unable to demonstrate “size dimorphism between the sexes” which was suggested by Cort from his studies on an eye-spotted non-mammalian schistosome, in spite of most careful measurements of a large number of cercariae from many infested snails. 2. Beneath the circular and longitudinal musle layers is found a layer of diagonal muscle in the anterior half of the bodywall. 3. There are certain numbers of sensory organ (a process with a delicate hair) on the surface of the body and tail. 4. There are four retractor muscle bands in the anterior tip of the body. 5. A pair of granular cell groups which lie in the posterior region of the body of young cercaria remove into anterior body region (anterior organ) at all once at the time the cercaria is almost developed, and from characteristic sacs-a sort of syncytium. These sacs are namely “head gland” (of Narabayashi). But they have no function of secretion at all; it seems highly probable that they function mechanically to assist the penetration of the cercaria into the final host as a auxiliary apparatus of pushing out of the fore part of the anterior body region in cooperation with the boundary muscle. By above-mentioned views I wish to propose the name “head sac” instead of “head gland”. 6. Three pairs of retractor muscle bands radiate from the proximal region of the ventral sucker to the dorsal side of the body, where they are inserted. 7. From each ganglion two nerve stems run dorsally and ventrally, and each of them directly bifurcates into anterior and posterior nerve strands, which run respectively to the both ends of the body. 8. Two distinct type of movements, peristalsis and rythmic segmentation, are observed on the oesophagus. 9. Two special flame cells are recognized instead of the cilia which described by Cort as “ciliated area”, in the beginning part of each main collecting tube. 10. The ducts of poison glands (penetration gland) are fixed in x-shape by three pairs of muscle bands on the level of the ganglion. 11. Each opening of the poison glands has hair bush, which act probably as a closing apparatus. 12. There are definite morphological and microchemical distinctions between an anterior (2 pairs) and posterior (3 pairs) group of poison glands.
13. Five pairs of head spines (anterior spine) are found on the anterior tip of the body: three of them on the dorsal side and two (much smaller than the former) of them on the ventral side. Opposite to the Faust's description, each of head spines is not hollow in the center and does not cap the opening of the poison gland. 14. In the main stem of the tail are found circular, longitudinal and diagonal muscle layers. 15. The tail furcae take two distinct manners at swimming: 1) at body forward the furcae close together and agree with the axis of the tail-stem; 2) at tail forward the furcae open separately and make right angles to the tail-stem.