miracidium of Megalodiscus temperatus, the rectal fluke of Rana pipiens. This is a section through the apical papilla which attaches to its specific  ram horn snail host, Helisoma trivolvis during the penetration act. There are four different glands, each carrying different secretory vesicles, depositing secretions on the surface of the snail, aiding in  penetration.  The four types of glands are penetration glands (PG), secretory sac (SS), and accessory penetration glands (AC). The fourth type, the apical gland is not seen here.   The open spaces are the pores of  three of the different types of secretory glands.  30,000x.