Sigma Class Glutathione Transferase of F. hepatica www.plosntds.org development concomitant with an exponential decrease of PGD 2 levels over the next 120 h post fertilisation [59] . However, in F. hepatica, eggs in gravid adults are released in an immature state in the bile duct, where they pass to the external environment via the host's excretory system and complete embryogenesis ex-host. Therefore, FhGST-S1 may have a secondary, or indeed primary, function in egg development and embyrogenesis. A role in egg development is further supported by proteomic studies of F. hepatica ontogenic stages which reveal the presence of FhGST-S1 in eggs ( [42] and the current study).