110 DISTRIBUTION OF MITOCHONDRIA IN THE PLACENTA. 



being pinched off by pressure from new cells arising next to the basement membrane. 

 Usually, each cell contains a single nucleus which may be located in any part of the 

 apex, depending upon the pressure from surrounding cells. However, cells contain- 

 ing two or three nuclei are not rare. The nucleus has a very indefinite limiting 

 membrane and its outline is irregularly stellate, apparently from the pressure of 

 vacuoles in the protoplasm which indent its surface and may almost completely 

 divide it. It stains rather deep green and contains a single large fuchsinophilic 

 nucleolus. The cytoplasm stains a faint green and is crowded with vacuoles of 

 fairly uniform size, about 1 M in diameter. In the apices of a few of the cells are large 

 vacuoles containing fragments of phagocytosed red blood-cells. The mitochondria 

 are not numerous and are seen as small granules and short rods lying between the 

 vacuoles. They are not concentrated in any particular part of the cell. 



The allantoic membrane consists of a single layer of flattened cells resting on a 

 delicate basement membrane. The free surface of the cells is covered with debris. 

 The nucleus is oval or flattened, stains a rather deep green and contains a single 

 fuchsinophilic nucleolus and several irregular masses of chromatin. The pale-green 

 protoplasm is finely vacuolated and contains a few small granular mitochondria. 



PLACENTA OF THE GUINEA-PIG. 



The vitelline membrane of the guinea-pig consists of a single layer of columnar 

 cells of medium height resting on a basement membrane which is supported by a 

 layer of connective tissue rich in small blood-vessels. The membrane is thrown into 

 folds and numerous villi project from its surface. The columnar cells have dome- 

 like apices which bulge out from the points of contact with the surrounding cells 

 and this, in addition to the variation in height of the cells, gives an irregularly 

 serrated edge to a cross-section of the membrane. In the central portion of each 

 cell there is a light-green nucleus which contains from one to four fuchsinophilic 

 nucleoli. The protoplasm of the apical zone stains a light green, while that of the 

 basal zone is clear and unstained. Two to six small, clear vacuoles are usually 

 seen in the apical zone. In the more senile cells the protoplasm contains vacuoles of 

 varying size. They may be quite large and may occupy any part of the cell. 



A variable number of fuchsinophilic granules are constantly present in these 

 cells. They vary from a few small granules to a large number of coarse globules 

 2 n in diameter. When only a few are present they are located in the basal zone 

 and around the nucleus, leaving the basophilic apex clear. They are apparently 

 not products of degeneration, as they are present in all cells. 



The mitochondria are not very numerous. They are mostly in the form of 

 small rods, though a few minute granules are constantly present. In the average cell 

 they are limited to the base of the cell and the zone around the nucleus and are 

 distributed throughout the protoplasm. Apparently there is no quantitative rela- 

 tion between the mitochondria and the fuchsinophilic granules, as cells containing 

 a large number of granules may contain either a very few or a relative abundance of 

 mitochondria. Senile cells contain very few or no mitochondria. Senility, how- 

 ever, apparently does not affect the number of fuchsinophilic granules, as wide 

 variations are found in cells with pycnotic nuclei and vacuolated protoplasm. 



