miracidium of Megalodiscus temperatus from Rana pipiens.  This section includes the brain or ganglion in the center of the field containing small adrenergic vesicles.  The large globules to the right are secretory vesicles of the secretory sac.  The curved row of humps are circular muscles located just below the longitudinal band of muscles.  The fibers of the circular and longitudinal muscles run perpendicular to one another.  10,000x