The finestructural changes of the interareolar porcine placenta during pregnancy are described. After perfusion fixation of the placenta the change in the thickness of the placental barrier from day 30 to day 110 of gestation is much more evident than after immerson fixation as has been used by all former authors. The alterations are due to the indentation of both the trophoblast and uterine epithelium by their corresponding capillary-network. This indentation is limited to the lateral wall and the summit of the chorionic ridges, while at the base the trophoblast as well as the uterine epithelium remains high columnar. This indicates that in the interareolar porcine placenta, which is represented by the chorionic ridges and the corresponding endometrial folds, at least two different areas with different structure and function may be discerned. 1) The lateral side and the top of the chorionic ridges seem to be predestinated for gaseous exchange. The placental barrier in this area is often less than 2 micrometers. 2) The transport of blood-borne nutrients takes place at the base of the chorionic ridges. This transport seems to be facilitated by an intercellular channel system between the uterine epithelial cells.

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The ultrastructure of the areolae in the porcine placenta is described. The areolae occur on day 30 of pregnancy as dome-shaped formation over the openings of the uterine glands. The lumen of the areolae is filled with the secretions of the uterine glands, the so-called histiotroph. The areolae lining epithelium is high collumnar, possessing long microvilli, a well-developed apical tubular system and numerous coated vesicles. This indicates that the epithelium has a high absorptive capacity. Our histochemical investigations reveal a high content of glycoproteins within the areolar lumen. The importance of one of the glycoprotein components of the histiotroph, uteroferrin, is discussed in connection with iron transfer from mother to the fetus.

The histochemical localization of five glycosidases was studied in the epididymis of mature dogs. beta-Galactosidase showed a distinct to strong reaction in the epithelium of the ductuli efferentes and throughout the whole length of the ductus epididymidis. beta-N-Acetylglucosaminidase reactivity was weak in the initial segment, but increased significantly in the middle and terminal segment. The maximum beta-glucuronidase activity was found in the ductuli efferentes and in the initial segment. The alpha-mannosidase reaction was weak in all segments except the middle segment where a distinct activity was seen. With the method employed, no alpha-fucosidase activity could be detected. The physiological role of the glycosidases in the epididymis is discussed briefly.