456 THE PHYSIOLOGY OF REPRODUCTION 



Mole. The method of embedding is centric. A simple 

 yolk-sac placenta exists for a time. The allantoic placenta is 

 discoid and is placed anti-mesometrially. The glandular secretion 

 is of importance for the nourishment of the developing foetus 

 during the greater part of pregnancy (Strahl, 1 Vernhout 2 ). 



At the beginning of pregnancy the mucosa shows variations 

 in its different parts. Near the mesometrium, for about one- 

 third of the circumference of the lumen, the glandular layer is 

 thin. Anti-mesometrially the muscular layer is not so well 

 developed, but superficially to the glands there is a proliferation 

 of connective tissue cells, through which the ducts run to open 

 into the lumen. The first attachment is in this region. 



The uterine horns show a series of small swellings where the 

 ova are present. The blastocysts grow to a comparatively 

 large size, and completely fill up the lumen. By their further 

 growth, the epithelium near the mesometrium is flattened and 

 replaced by trophoblastic cells, which do not penetrate into the 

 connective tissue or form villi. Hence the yolk-sac placenta is 

 is of a simple type ; it persists throughout pregnancy. 



On the opposite side the decidual formation proceeds, and 

 the mucosa becomes thicker. In its substance a rich network 

 of blood-capillaries is developed. The epithelial cells lose their 

 boundaries and form a symplasma. According to Strahl this 

 remains, and forms the syncytial covering of the future villi, but 

 Vernhout has shown that the trophoblast proliferates and forms 

 a layer of epithelioid cells which penetrate into the epithelium 

 and absorb and gradually replace it. Over each gland-opening 

 the trophoblast forms a dome as in Ruminants (Fig. 117). In 

 the placental region the glandular epithelium is not changed, 

 and around each opening a small area of the surrounding 

 uterine epithelium persists. In the cavity between a gland-orifice 

 and its trophoblastic cap lies a dark secretion, pigmented by 

 admixture with extravasated blood, and the cap is similarly 

 pigmented. Hence the secretion is probably absorbed by the 

 foetal ectoderm throughout the greater part of pregnancy during 

 which the glands remain. After the disappearance of the surface 



1 Strahl, " Ueber den Ban der Placenta von Talpa europea" Anat. Am., 

 vol. T M 1890. 



2 Vernhout, Ueber die Placenta des Maulwurfs," Anat. Hefte, vol. v.,1894. 



