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The oogenotop was studied using certain histochemical tests and the contributions of the various parts to the egg were noted. The Mehlis gland and the uterine epithelium make large contributions to the egg. Both the inner and outer envelopes are of reduced importance. A photographic record of oogenesis is presented showing it follows previous descriptions for the Cestoda. The first cleavage is unequal. Shell granules from the oocyte are carried to the macromeres where they are used in the formation of the outer capsule. Hatching is standard for eggs with a membraneous inner capsule. Most infections are characterized by one female and one male worm. Microsporidians reduce the number of sperm produced and probably limit the production of oncospheres.

Mehlis' gland of F. hepatica is composed of two secretory cell types supported by parenchymal cells. The products of the secretory cells are carried by means of cytoplasmic extensions into the ootype. The most prevalent type of secretory cell is termed S 1 type. It possesses many narrow granular endoplasmic cisternae and numerous Golgi complexes. The secretory bodies of this cell resemble slightly curved sausages and have a filamentous content radiating from a central core. The other secretory cell type is termed S2 type. It is characterized by distended granular endoplasmic cisternae and numerous Golgi complexes which give rise to round dense secretory bodies with a crystalline or packed fibrous appearance. Both types of secretory cells are penetrated deeply by invaginations of interstitial material. The cytoplasmic extensions from the cells are lined with microtubules and anchored to the epithelial cells lining the ootype by septate desmosomes. The secretory bodies of both cell types are released into the lumen of the ootype, where they disintegrate.

The cells of Mehlis's gland in the liver fluke (Fasciola hepatica L.) have been studied with light and electron microscopy. The gland contained large cells in the periphery and small cells in the centre. The large cells presented morphological features characteristic of secretory cells, viz. large nucleoli, cytoplasmic basophilia, a well developed endoplasmic reticulum, abundant ribosomes, and secretory granules in different stages of development. The mitochondria were moderately frequent. Several small groups of vesicles and membraneous lamellae reminiscent of Golgi complexes occurred randomly in the cytoplasm. These structures were associated with mitochondria and secretory granules. Evidence of alterations and conversion into a cell debris was observed, and a process of holocrine secretion was suggested.