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The ultrastructure of helminth. 4. Cercaria of Schistosoma japonicum.

The body wall of the cercaria of Schistosoma japonicum is covered with a thin integument which is connected to epithel cells located under the uscle layer. On the outer and the basal surfaces of the integument are seen thin limiting membranes. In the matrix of the integument are distributed numerous dense granules, vacuoles and spines. The rootlet of the spine is attached to the basement membrane of the integument. The circular and longitudinal muscle layers, both underlying the integument, have smooth muscle fibers composed of thick and thin myofilaments.
The cercaria possesses five pairs of secretion gland cells which are divided into two groups of three anterior and two posterior pairs. Both gland cells are filled with secretion balls. The tail of cercaria is likewise covered with a thin integumen t, whose structure is identically the same as the body integument. Beneath the integument are located thin circular and longitudinal muscle layers. The circular muscle cells have smooth muscle fibers, but the longitudinal muscle cells have striated muscle fibers. These muscle cells contain many large mitochondria. On observing the cross-sections of the tail at the flame cell level the arrangement of these muscle can be divided into four muscle groups and each muscle group reveals four or five muscle cells. The excretory system is well developed and has flame cells, excretory canal and bladder.