In 6 week-old Paramphistomum cervi, vitelline cells appear in the form of a few scattered cells, present below the body wall which divide mitotically to form vitelline follicles in 8 week-old worms. Small shell globules appear first in 10 week-old worms, the number and size of which continue to increase till the worm becomes adult. In the latter the vitelline follicles contain stem cells, immature, maturing and mature vitelline cells, which differ due to the distribution of shell globules as well as their histochemical nature. The shell globules are keratin in nature. The vitelline cells showed activities of various phosphatases but did not show the presence of any of the dehydrogenases studied.

The formation of the egg mass in the ootype, containing the oocyte, vitelline cells, numerous spermatozoa and Mehlis’ gland secretion marks the beginning of eggshell formation. Mehlis’ gland cells pour their lipoprotein secretion into the ootype; this secretion forms a thin template around the egg mass and upon this template the shell globules are deposited. Eggshell formation begins in the proximal uterus and is completed in the middle uterus. The eggshells are devoid of phenols and phenolase indicating that hardening is not by quinone tanning. The eggshells contain keratin and are stabilized by disulphide linkages.

The tegument of Orthocoelium scoliocoelium and Paramphistomum cervi was examined using histochemical techniques and electron microscopy. On the basis of the distribution of acid and alkaline phosphatase (E.C. 3.1.3.2, E.C. 3.1.3.1), non-specific esterase (E.C. 3.1.1.1), cholinesterase (E.C. 3.1.1.7) and succinate dehydrogenase (E.C. 1.3.99.1) at light microscope level two distinct regions were recognized, an outer and an inner zone. Electron microscopy revealed that the tegument comprises an outer surface syncytium underlain by a thick subsyncytial zone and musculature. Deeper still occur the nucleated “tegumental cells”. The latter are in cytoplasmic continuity with the surface syncytium via vacuolated cytoplasmic trabeculae which traverse the muscle layers and the subsyncytial zone. Three types of tegumental cells each lacking mitochondria were observed. The T1 cells synthesize discoid and electron dense T1 bodies while T2 cells produce oval and electron lucent T2 bodies. The third type of tegumental cells apparently produce no secretory bodies and may represent an embryonic cell type. The surface syncytium contains T1 and T2 secretory bodies and is bounded apically by a plasma membrane invested externally by a fuzzy and filamentous glycocalyx. The surface syncytium lacks mitochondria and is traversed by infoldings of the basal plasma membrane. Beneath the surface syncytium the subsyncytial zone is largely comprised of fibrous interstitial material. This zone, which is particularly thick in the amphistomes, is traversed by trabeculae and extensions of underlying parenchymal cells which usually contain mitochondria and lysosomes. The subsyncytial zone overlies numerous circular and longitudinal muscle fibres. The absence of mitochondria and enzymes associated with active transport suggests that the amphistome tegument may be mainly specialized for protection of the worm against mechanical and chemical conditions prevailing in the rumen. Active uptake of nutrients is probably not a primary function.