Here is some information about cestodes’ anatomy and physiology:
Scolex and proglottids: the scolex (head) is the point of attachment between the host and the parasite, and it contains nerves terminating in ganglia. Each proglottid has two layers of muscle that allows the segment to move. Segments are anatomically independent, but they are all connected by a common nervous system emanating from central ganglia located in the scolex. The neck region of the scolex is metabolically active and is the site where most tapeworms form new proglottids.
Figure 3. Scolex and proglottids of Hymenolepis nana
Nutrient acquisition: segments are enclosed in the tegument, whose structure and function is directly related to nutrient acquisition. Evenly spaced microvilli cover the entire surface of the tegument that allows for active transport of the nutrients across the tegument.
Reproduction: mature proglottids are hermaphrodites (possess both male and female sex organs). What usually happens is that sperm is transferred between mature proglottids that lie next to each other. Gravid proglottids develop after mating, and contain hundreds to thousands of embryonated eggs. The gravid proglottids then detach from the parent organism and exit via the host's anus.
What happens with the eggs? eggs are usually released embryonated, and contain a larva referred to as an oncosphere. Once ingested by an intermediate host, it hatches within the small intestine, allowing the oncosphere to penetrate the GI tract and lodge within the tissue (now called metacestode). When this stage is ingested by the definitive host, it transforms to the adult in the lumen of the small intestine.
