42 K Uptake by Tissues in Pregnant Animals 155 



Morphological observations 



The experimental observations outlined above made 

 available material from a series of animals killed after a 

 known period of pregnancy. Material from other goats, also 

 of known gestation age, has resulted in the examination of 

 over sixty animals killed at different stages of pregnancy. 



Recent papers on the developmental changes in the 

 placenta of the Artiodactyla include those by Wimsatt (1950, 

 1951), Harrison and Hamilton (1952), Bjorkman (1954) and 

 Harrison and Hyett (1954). A full review of earlier papers 

 on the placenta of the cow, sheep and pig has been given by 

 Amoroso (1952). 



The placenta of the goat is polycotyledonary with from 

 120 to 180 cup-shaped or concave placentomes (PL I, Fig. 5) 

 arranged more or less in rows. The placentomes on the meso- 

 metrial aspect of the central portion of each uterine horn are, 

 for the first third or more of pregnancy, substantially the larger. 

 As pregnancy advances the cranially placed placentomes 

 increase more rapidly in size than those centrally placed, but 

 do not reach a comparable size. Occasionally flattened, sessile, 

 oval placentomes are encountered together with the concave 

 variety, and in several animals killed during the middle of 

 pregnancy only the flattened, oval variety was present. It 

 should be noted that the uptake of radioactive potassium 

 by the two types of placentome was not significantly different. 

 It is not yet clear if this morphological difference is genetic in 

 origin, or a manifestation of change in the form of the placen- 

 tome during development. 



Primary villi are present and have penetrated deep into the 

 caruncular tissue even by the 39th day of pregnancy (PL I, 

 Fig. 4). The primary villi are at first straight and simple, 

 but active division at their tips results in the formation of 

 secondary and tertiary villi, each fitting into a corresponding 

 maternal crypt. From the earliest stages studied (35th day) 

 it appears that the trophoblast has considerable powers of 

 attrition and the maternal epithelium is destroyed not only 

 in the crypt walls but also in localized areas in relation to the 



