* Present address: Bernard Matthews Foods Ltd, Great Witchingham Hall, Norwich, NR9 5QD, U.K.
** Corresponding author: e-mail:email@example.com
An ultrastructural study has been made of the egg assembly apparatus of the monopisthocotylean monogenean skin parasites Entobdella soleae and E. hippoglossi from the common sole, Solea solea, and the halibut, Hippoglossus hippoglossus, respectively. The ootype consists of a distal tetrahedral chamber where the egg capsule is assembled and a proximal ootype tube where the egg appendage is made. Two types of Mehlis' gland (alpha and beta) open at the proximal end of the ootype tube, which has a non-secretory lining. In both species, the tetrahedral ootype chamber has a syncytial lining, which apparently is not secretory and possesses on its luminal surface stud-like projections, each with vacuolated cytoplasm and an electron-dense core. The ootype chamber is enclosed by a single layer of muscle fibres and is embedded in a spongy "connective tissue". The uterus in E. soleae has a cellular secretory lining, with densely packed luminal microvilli.