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