156 R. J. Harrison and J. L. D'Silva 



membranous or intercotyledonary chorion (PL I, Figs. 1 and 

 3). Near the edges of the developing caruncles the chorion is 

 thrown into folds or intermediate villi, the areas thus resemble 

 the arcade formations described by Assheton (1906) and 

 Bjorkman (1954). The maternal epithelium also shows signs 

 of impending degeneration in the septal walls surrounding 

 the intermediate villi (PL I, Fig. 2). Only in the regions of the 

 mouths of the uterine glands does the maternal epithelium 

 display the characteristics of healthy tissue, and where the 

 chorion comes into contact at the edges of the gland mouth 

 localized areas of cellular attrition are present (PL I, Fig. 3). 

 The powers of attrition apparently possessed by the 

 chorionic epithelium may be reflected by the increase in 

 density of the sub-epithelial stratum compactum to a degree 

 greater than that observed by Hamilton and Harrison (1951) 

 in the non-pregnant uterus of the goat. This increase in 

 density appears to be due not only to changes in the cellular 

 population but also to increase in the quantity of connective 

 tissue and changes in its staining qualities and also in those 

 of the intercellular substance. It is noticeable that the de- 

 struction of maternal tissue attributable to the chorion is 

 capable of causing localized haemorrhages between foetal and 

 maternal tissues. Such haemorrhages can be seen in early 



PLATE I 



Fig. 1. Photomicrograph to show destruction of the maternal epithelium 

 during the early stages of pregnancy. The animal had been pregnant for 30 



days. Section stained by the P.A.S. method, x 70. 

 Fig. 2. Photomicrograph to show the formation of folds in the chorion at the 

 edge of the developing caruncle. The animal had been pregnant for 30 days. 



Haematoxylin and eosin. x 70. 

 Fig. 3. Photomicrograph of a membranous chorion in relation to the mouth 

 of a maternal gland. The animal had been pregnant for 30 days. Haematoxylin 



and eosin. x 75. 

 Fig. 4. Photomicrograph to show the appearance of the young villi in the 

 developing caruncle at the 30th day of pregnancy. Haematoxylin and eosin. 



X 42. 

 Fig. 5. The appearances of the placentomes on the 50th day of pregnancy, 

 showing haemorrhages on the surfaces of the placentomes. x £. 

 Fig. 6. Photomicrograph of a small accessory placentome on the 66th day 

 of pregnancy, showing an extravasation of blood between the maternal and 



foetal tissues. 



