ELECTRON MICROSCOPIC OBSERVATIONS ON THE PLACENTA OF THE CAT

During the pas t several years, cytological, histochemical, and electron microscopic studies have been carried out on the placentas of several different species of mammals . I n these studies, par t icu lar a t ten t ion has been pa id to the so called placental barr ier ; t ha t is, the regions of the chorial lantoic p lacenta in which the circulating fetal blood most closely approximates the materna l blood. We have also invest igated certain other specialized p lacenta l structures, such as the yolk sac in rodents, lagomorphs, and the mare, the brown and green borders or parap lacenta l chorion of the cat and dog, respectively, and the endometr ia l cups of the p lacenta of the mare. These various s tructures are of par t icu lar interest since there is evidence tha t each par t ic ipates in some par t icu lar p lacenta l funct ion; the yolk sac of rabbi t s in the transmission of mate rna l ant ibodies to the fetus (Brambell , Rogers, Hemmings, and Henderson, 1951), the parap lacenta l chorion of carnivores in the transmission of iron to the fetus, and the mare ' s endometr ia l cups in the product ion of the hormone character is t ic of pregnant mare serum. The present invest igat ion extends our studies by presenting observat ions with the electron microscope upon the chorioallantoic p lacenta and the paraplacenta l chorion or brown border in a carnivore, the domestic cat.