42 K Uptake by Tissues in Pregnant Animals 157 



pregnancy (PL I, Fig. 6), the middle of pregnancy (PL I, Fig. 5), 

 and in late pregnancy it is common to find evidence of both 

 early and more recent haemorrhages in one area of the edge 

 of the placentome. 



From about the 45th day of pregnancy numerous laterally 

 directed branches develop all along the extent of each primary 

 villus. These side branches divide frequently and extend into 

 the crypt walls. The latter are soon extensively invaded 

 (PL II, Fig. 2) and examination of the specimens killed during 

 the latter third and terminal stages of pregnancy suggests 

 that there is a gradual attrition of the tissue surrounding each 

 maternal capillary. Near term much of the crypt wall has 

 been lost and only remains as strands of tissue connecting and 

 surrounding the network of maternal vessels (PL II, Fig. 5). 

 There appears to be a change in the characteristics of the 

 septal connective tissue in that it becomes more markedly 

 P.A.S. positive with the advancement of pregnancy (PL II, 

 Figs. 3 and 4). 



Examination of the membranous chorion during the latter 

 part of pregnancy suggests that the destructive powers of 

 the chorion are not necessarily restricted to the earlier period 

 (PL II, Fig. 1). It is possible that there may be efforts to 

 renew the maternal uterine epithelium by regeneration from 

 the intact epithelium of the gland mouths. In any event there 



PLATE II 



Fig. 1. Photomicrograph to show the appearances of the membranous chorion 

 at about the 90th day of pregnancy, and the relationship of the chorion to the 



mouth of the uterine gland. Haematoxylin and eosin. x 94. 

 Fig. 2. Photomicrograph to show branching of the villi within the placentome 



of an animal pregnant for 96 days. Haematoxylin and eosin. x 28. 

 Fig. 3. Photomicrograph showing the tips of the villi within the maternal 

 crypts at the 86th day of pregnancy. The section is stained by the P.A.S. 

 method and shows the foetal giant cells, and also the connective tissue of the 



crypt cells. X 68. 

 Fig. 4. Photomicrograph to show the bases of the foetal villi where they enter 

 the maternal crypts ; also showing the mouths of the crypts. Section stained 



by the P.A.S. method, x 50. 

 Fig. 5. Photomicrograph of the branches of the villi and the maternal capil- 

 laries in the centre of a placentome at the 142nd day of pregnancy. Haema- 

 toxylin and eosin. x 175. 



