910 



SPERM, OVA, AND PREGNANCY 



plasma membranes. Thus, there is far more 

 intimate apposition than was previously 

 realized and also these ultrastructural de- 

 vices result in a great expansion of surface 

 area. Furthermore, the uterine space at this 

 maternal-fetal junction is so slight that the 

 possibility of absorption of uterine secre- 

 tions through the chorionic ridges and fos- 

 sae seems to be excluded. Uterine secretions 

 are most likely absorbed through the cho- 

 rionic areolae which occur in regions where 

 the uterine lumen is patent and filled with 

 secretion. The special chorionic epithelium 

 of the areolae shows great complexity at its 

 surface. In addition to possessing irregularly 

 shaped, often bulbous, projections which 

 extend into the uterine lumen, these cells 

 have complicated infoldings of the plasma 

 membrane both apically and laterally. Dur- 

 ing the latter half of gestation, the fetal 

 capillaries burrow into the chorionic epi- 

 thelium where they acquire a so-called in- 

 tra-epithelial position; fetal capillaries are 

 especially rich in the chorionic ridges. The 

 electron microscope has revealed that two 

 basement membranes remain interposed be- 

 tween the chorionic epithelium and endo- 

 thelium. Further interesting observations 

 on the pig placenta concern the possibility 

 of secretory activity by the cells lining the 

 chorionic fossae and the occurrence of oc- 

 casional cilia in the uterine glands. 



The placenta of the cat, according to 

 Grosser's classification, is of the endothelio- 

 chorial type in which erosion of the uterine 

 epithelium and connective tissue occurs. 

 The placenta proper consists of a series 

 of roughly parallel trophoblastic plates or 

 lamellae (Figs. 15.56, 15.60, and 15.61). In 

 the center of the lamellae, maternal blood 

 flows through closed capillaries surrounded 

 by a relatively thick amorphous matrix and 

 occasional giant decidual cells of maternal 

 origin. The syncytiotrophoblast abuts on 

 the amorphous matrix. The cytotrophoblast, 

 which diminishes as gestation proceeds, is 

 situated between the syncytiotrophoblast 

 and the fetal connective tissue. The tropho- 

 blastic lamellae are separated from each 

 other by a layer of fetal connective tissue 

 through which fetal capillaries course. 



Some observations on the ultrastructure 

 of the placental and paraplacental regions 

 of the cat's chorion were reported by 

 Dempsey and Wislocki (1956). Substances 

 passing from the maternal blood to that of 

 the fetus first encounter the unusually thick 

 and basophilic maternal endothelium which 

 typifies the capillaries of the carnivore pla- 

 centas. The endothelial cytoplasm evagi- 

 nates to form surface projections and ap- 

 pears to have a well developed endoplasmic 

 reticulum; however, inadequate preserva- 

 tion of these cells does not permit further 



Plate 15. VIII 



All of the photographs on this plate are of a normal human placenta of 6 weeks of gesta- 

 tion. 



Figs. 15.33, 15.34 and 15.35. The localization of sulfhydryl groups by Barnett and Selig- 

 man's method. The reaction is most intense in the trophoblastic .syncytium where it is es- 

 pecially pronounced at the inner and outer borders (Fig. 15.33). The Langhans cells give the 

 least reaction, being set off as clear cells which appear to be enclosed by dark capsules (Figs. 

 15.33 and 15.34). The peripheral cytotrophoblasts and the stromal cells of the chorionic 

 villi are also moderately reactive (Fig. 15.35). X 300. 



Fig. 15.36. The enzymatic reaction of esterase by Barrnett and Seligman's method is con- 

 fined principally to the trophoblast clothing the villi, although small scattered particles of 

 the reaction product are also present in the stroma. As explained in the text, it is believed 

 that the reaction seen should be attributed to cholinesterase. X 175. 



Fig. 15.37. The reaction of Seligman and Rutenberg for succinic dehydrogenase. Blue crys- 

 tals of diformazan are produced which are indicative of enzymatic activity. This reaction 

 product is soluble in lipids which it stains pink, but this color has been eliminated in the 

 picture by photographing the section through a red filter (Wratten A 25). The succinic de- 

 hydrogenase reaction indicated by blue diformazan particles is present in the syncytium and 

 Langhans cells. Very little reaction has occurred in the cells of the stroma. X 250. 



Fig. 15.38. Illustrates the combined appearance of the blue diformazan particles and the 

 pink-stained fat droplets. Compare with Figure 15.37 in which the color of the latter has been 

 reduced. The stained lipid is identical with the sudanophilic droplets pre.sent in the syncytium 

 (c/. Fig. 15.13). In the lower half of this figure clear nuclei of cytotrophoblasts are barely ap- 

 parent, surrounded by cj^toplasm containing diformazan crystals. X 200. 



