. The physiology of reproduction. Reproduction. 398 THE PHYSIOLOGY OF REPRODUCTION fit into depressions or crypts on the surface of the cotyledons, increase in length, and branch in different directions. Whether they Hterally grow into the maternal tissues either mechanically or by a phagocytic action is uncertain/ It seems more hkely that very httle, if any, further penetration occurs, but that the sub-epitheUal tissue swells and keeps pace with the viUi as they increase in length. The crypts, if their hning cells really belong to the foetal ectoderm, are not secretory, and there is no free s
. The physiology of reproduction. Reproduction. 398 THE PHYSIOLOGY OF REPRODUCTION fit into depressions or crypts on the surface of the cotyledons, increase in length, and branch in different directions. Whether they Hterally grow into the maternal tissues either mechanically or by a phagocytic action is uncertain/ It seems more hkely that very httle, if any, further penetration occurs, but that the sub-epitheUal tissue swells and keeps pace with the viUi as they increase in length. The crypts, if their hning cells really belong to the foetal ectoderm, are not secretory, and there is no free space, such as is described in the mare, between them and the villi. The sub-epithehal tissue is represented in the non-. FiG. 90,—Section through the uterine and embryonic parts of a cotyledon of the sheep at the twentieth day of pregnancy. Folds in the tropho- blast fitting into sulci of the cotyledonary burr. (Assheton.) mes, mesoblast; tr, trophoblast; Ms, degenerated uterine epithelium ; sir, uterine stroma. pregnant uterus by a thin layer of dense connective tissue, with locahsed thickenings in the burrs. With the onset of pregnancy occur an infiltration of lymph between the more superficial cells of the sub-epithehal layer, and an increase in the number and size of the blood-capillaries and lymphatics. Thus the layer becomes spongy and swells up around the foetal vilh, producing the cotyledonary interdigitation. At the fundus of the crypts the hning cells become syncytial. At the apices of the inter-crypt columns lacunae of maternal blood are formed by repeated small haemorrhages from the superficial capillaries (Fig. 91). 1 At this stage Assheton did not observe any actual engulfment of cells, but considered that nutriment might be transmitted by fine processes of the binucleate cells wliich united with similar processes of the connective tissue cells of the Please note that these images are extracted from scanned page images that may have been digitally enhan
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