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The ‘secretory pathway’ of the Mehlis' gland secretion as well as the maturation of the secretory granules are described. The secretions produced by the Mehlis' gland and the distal ootype in Schistosoma mansoni were identified as neutral glycoproteins. They were both periodate reactive, stained with phosphotungstic acid at low pH, and sensitive to the proteolytic action of papain. The secretions did not strain with both the low-iron diamine and the high-iron diamine methods for the presence of acidic glycoconjugates, and they did not contain a detectable level of sulphydryl groups. The possible role of the secretion from the Mehlis' gland in egg-shell formation is discussed.

The ancyrocephaline monogenean gill parasite Cichlidogyrus halli typicus has a short oviduct/ovo-vitelline duct separated from the germarium and from the ootype by sphincter muscles. The chamber so-formed contains spermatozoa, the axonemal ends of which appear to be attached in an intimate way between lamellated extensions of the chamber lining. This arrangement may facilitate fertilization by retaining an oocyte temporarily in close contact with the free nucleated ends of the spermatozoa, i.e. the short oviduct/ovo-vitelline duct may serve as a fertilization chamber. There are two distinct types of Mehlis' gland opening at the base of the ootype and the latter has a cellular, non-secretory lining which is not penetrated by gland ducts.

Mehlis' gland of both Diplozoon paradoxum and Calicotyle kroyeri is composed of two cell types that taper to form ducts opening into the lumen of the ootype. The cells are invested with fibrous interstitial material and form a close structural relationship with surrounding parenchyma. The most prevalent cell type, the S 1 cell, is characterized by an extensive GER with narrow cisternae containing a finely granular material, and numerous Golgi stacks involved in the formation of multi-vesicular secretory bodies. In the S 2 cells the GER cisternae are greatly distended with a finely filamentous material and the Golgi give rise to dense secretory bodies with a packed fibrous appearance. There are species differences in the fine structure of the secretory bodies and these may reflect differences in the chemical composition of the glands. The ducts of the glands are lined with microtubules and are anchored to the ootype epithelium by septate desmosomes. They convey the secretory products to the ootype where they are released, apparently by exocytosis involving membrane fusion, into the lumen. The ootype is lined by a highly folded cellular epithelium which in D. paradoxum is ciliated. The cells contain profiles of GER and Golgi complexes and produce a third type of secretion which is also discharged into the ootype lumen.